Nelsonioideae (Lamiales: Acanthaceae): Revision of Genera and Catalog of Species

A taxonomic account of Acanthaceae subfamily Nelsonioideae based on morphological and phylogenetic data treats five genera with 172 species: Anisosepalum (3), Elytraria (21), Nelsonia (2), Saintpauliopsis (1), and Staurogyne (145). Two other currently recognized genera, Gynocraterium and Ophiorrhiziphyllon, are included within Staurogyne, and the new combinations, Staurogyne guianensis and S. macrobotrya, are proposed. Probable apomorphic and other diagnostic macroand micromorphological characters are discussed relative to the subfamily and genera. Characters of the inflorescence, androecium (especially pollen), and seed show important phylogenetic and diagnostic signal. A key to genera, generic descriptions and discussions, illustrations, and distribution maps are provided. Lists of currently recognized species for each genus include synonymies and distributions by country.


INTRODUCTION
Acanthaceae consist of about 190 genera and 4750 species (Daniel unpubl.; vs. 212 genera and 3175 species fide Mabberley 2008). The family is pantropical in distribution, although most genera are restricted to either the New World or the Old World. Recent phylogenetic studies (e.g., McDade et al. 2008;Fig. 1) reveal the family to be monophyletic and divisible into at least three subfamilies that are related as follows: Nelsonioideae (Thunbergioideae + Acanthoideae). Nelsonioideae, the smallest among the currently recognized subfamilies, are here treated as consisting of 172 species in five genera: Anisosepalum (3), Elytraria (21), Nelsonia (2), Saintpauliopsis (1), and Staurogyne (145). Geographic occurrence and morphological diversity of Nelsonioideae reflect that of the entire family: they are nearly worldwide in distribution and show considerable variation in habit, foliar characteristics, and floral features.
Nelsonioideae have had a convoluted taxonomic history with respect to constituent genera, familial affinities, and taxonomic rank. Nees (1832Nees ( , 1847a treated genera now known as Elytraria, Nelsonia, and Staurogyne as tribe Nelsonieae of Acanthaceae; these were characterized by having small seeds that were not supported by conspicuous retinacula. Bentham and Hooker (1876) recognized this tribe and also included Ophiorrhiziphyllon in it. In the most comprehensive and influential account of Acanthaceae to date, Lindau (1895) treated these four genera in subfamily Nelsonioideae, which was characterized by having numerous seeds, papilliform retinacula, and tricolporate pollen. Van Tieghem (1908) segregated all genera lacking retinacula from Acanthaceae as a new family, Thunbergiaceae, with the nelsonioid assemblage remaining a subfamily. Wettstein (1924) returned Thunbergiaceae to Acanthaceae as a subfamily with the nelsonioids as a tribe of Thunbergioideae. In sequence, Bremekamp treated the nelsonioid genera as a subtribe of Acanthoideae: Acantheae (1938), as a tribe of Acanthoideae (1944), and finally, based primarily on the presence of persistent endosperm in their seeds, as a tribe of Scrophulariaceae: Rhinanthoideae (1953Rhinanthoideae ( , 1955. In the most extensive treatment of the nelsonioid assemblage to date, Hossain (1971Hossain ( , 1984Hossain ( , 2004 treated these genera (with the addition of Anisosepalum, Saintpauliopsis and Gynocraterium) as a tribe of Acanthaceae: Acanthoideae. Sreemadhavan (1977) and Lu (1990) have recognized nelsonioids as a distinct family, Nelsoniaceae. Treatment outside Acanthaceae (either as Scrophulariaceae sensu traditionalem or as a distinct family) never received widespread acceptance, and subfamilial rank has been generally utilized for the taxon (e.g., Cronquist 1981;Scotland and Vollesen 2000). Recent molecular phylogenetic studies (e.g., McDade et al. 2008McDade et al. , 2012 confirmed the subfamily as monophyletic, supported recognition of the five genera noted above, and placed the clade as sister to all other Acanthaceae. Some of the genera now treated as Nelsonioideae have been placed outside Acanthaceae. Neozenkerina, Ophiorrhiziphyllon, and Zenkerina (all 5 Staurogyne) were originally described in Scrophulariaceae, and Saintpauliopsis was originally described in Gesneriaceae. A further taxonomic complication is that both Nees (1847a) and Lindau (1895) included some genera now treated as Plantaginaceae (Adenosma R. Br.) and Orobanchaceae (Hiernia S. Moore) in their nelsonioid taxa. PHYLOGENY Because patterns of variation in macro-and micromorphological characters are best contextualized by phylogenetic relationships, we summarize recent phylogenetic results (Wenk and Daniel 2009;McDade et al. 2012) and then discuss plant characteristics. The subfamily is monophyletic and sister to all other Acanthaceae. Monophyly is also supported by at least one shared morphological character (possibly synapomorphic; this trait cannot be polarized with certainty until the closest relatives of Acanthaceae are clarified), descendingcochlear aestivation of corolla lobes. Aestivation patterns have been shown to be phylogenetically informative among Acanthaceae and, within the family this pattern is known only among Nelsonioideae (Scotland et al. 1994;Scotland and Vollesen 2000; additional observations by us for each genus). Therefore, there exists a basis for treating Nelsonioideae as a distinct and circumscribable (both morphologically and molecularly) family, as argued by Sreemadhavan (1977). McDade et al. (2012) provided data that support the recognition of at least five of the seven traditionally recognized genera of Nelsonioideae: Anisosepalum, Elytraria, Nelsonia, Saintpauliopsis, and Staurogyne. Relationships among these genera are summarized in Fig. 1. Nelsonia is monophyletic and sister to all other nelsonioids. We propose loss of bracteoles as a morphological synapomorphy for Nelsonia (versus paired bracteoles subtending each flower in other nelsonioids and, more broadly, Acanthaceae). Elytraria is also monophyletic and is sister to a ''staurogynoid'' clade consisting of all other genera of Nelsonioideae except Nelsonia. Elytraria can be delimited by at least three morphological synapomorphies: scaly peduncles, coriaceous to sclerophyllous bracts, and touch-sensitive stigmas. The existence of the ''staurogynoid'' clade was predicted by Hossain (2004) based on morphological similarities.Within this clade, monotypic Saintpauliopsis is sister to Anisosepalum and these together are sister to Staurogyne. Although no morphological synapomorphy for this ''staurogynoid'' clade has been identified, there is a tendency toward adnation of bracts to dichasial peduncles (cryptic epiphylly) in all three genera. Adnation of bracteoles to the base of flowers (i.e., receptacle and calyx tube) is likely synapomorphic for the clade consisting of Anisosepalum and Saintpauliopsis. Hossain (1972) indicated that Anisosepalum and Saintpauliopsis (unlike other genera of Nelsonioideae) lack acicular fibers in roots, stems, petioles, and veins; this might represent an anatomical synapomorphy for these two genera. The Asian genus Ophiorrhiziphyllon was shown to be nested among Asian taxa of Staurogyne, and the unispecific American genus Gynocraterium is sister to all of the sampled American species of Staurogyne. Although a case could be made for treating Gynocraterium as a distinct genus based on existing molecular data, this would involve considerable taxonomic renovations (see McDade et al. 2012), and there do not appear to be sufficient morphological grounds for such (see below under Staurogyne). As a result, we treat both Ophiorrhiziphyllon and Gynocraterium in an expanded Staurogyne. Thus, all genera recognized here are monophyletic based on molecular data and each is morphologically distinguishable. Morphological synapomorphies are known for all genera except for Staurogyne.

MORPHOLOGY
The subfamily can be characterized morphologically by several presumed symplesiomorphies and at least one probable synapomorphy (descending-cochlear aestivation of corolla lobes as described below). Traditionally, the lack of cystoliths and of indurate, hooklike structures (retinacula) subtending the seeds have been important in distinguishing Nelsonioideae (e.g., Lindau 1895). These presumably symplesiomorphic attributes are shared with both Avicennia and genera of Thunbergioideae. The absence of cystoliths is also shared with the basalmost tribe (Acantheae) of subfamily Acanthoideae. An additional distinguishing character usually associated with Nelsonioideae is the presence of persistent endosperm in their seeds (versus exalbuminous seeds in other acanths). Discussion of this and some additional morphological characters, highlighting phylogenetic patterns and variation among Nelsonioideae is presented below.

Habit
Species of Nelsonioideae are either herbs or shrubs. They are mostly terrestrial, but epiphytic or epipetric plants are known in Anisosepalum and Saintpauliopsis and probably occur sporadically in other genera. Herbs vary in duration from annual to perennial. Annual herbs are apparently not common. Both Elytraria marginata and Nelsonia gracilis are commonly noted to be annuals (e.g., Morton 1956;Dokosi 1971;Vollesen 2013). Cultivated plants of E. marginata (Daniel 11158cv at CAS) persisted only for one year and produced viable seeds that yielded plants lasting only a single year. While most collections of N. gracilis consist of plants that appear to be annual, some (see below) have larger and somewhat woody roots suggesting that other plants may also become perennial. Perennial herbs, with woody roots, caudices, or stems, are a more common growth form among the subfamily. Herbs vary from acaulescent (i.e., with a basal rosette of leaves) to subcaulescent (i.e., with slight internodal elongation at or just above ground level) to caulescent (up to 1 m or more high). Most herbaceous species are consistent in growth form, but some vary from acaulescent to subcaulescent (e.g., Elytraria acaulis, seen in Thwaites 240 at P), some from subcaulescent to caulescent (e.g., Elytraria marginata, seen in Adam 2058 at P), and some from acaulescent to caulescent (e.g., Nelsonia canescens, seen in Duthie s.n. from India at UC). Shrubs are uncommon in Anisosepalum (e.g., A. lewallei), Elytraria (e.g., E. nodosa), and Staurogyne (e.g., S. minarum), and do not occur at all in Nelsonia or Saintpauliopsis. The habit of plants in at least one species (E. imbricata) varies from acaulescent herbs to weak shrubs. Thus, there is no clear pattern of evolution of plant habits at the level of genus but the trait merits further examination once a densely sampled phylogeny of the largest genus, Staurogyne, is available.

Leaves
Nelsonioideae exhibit greater variation in foliar disposition and arrangement than the other main lineages of Acanthaceae. Plants with leaves 6 evenly disposed along stems occur in all genera; basal clusters of leaves occur in all genera except Anisosepalum; and apical/aerial clusters of leaves occur in some Elytraria. Arrangement of the leaves varies from alternate (some Elytraria, Nelsonia, and Staurogyne) to subopposite (some Staurogyne) to opposite (all genera except Elytraria) to whorled (Anisosepalum, Elytraria).
Leaves of Nelsonioideae are either sessile or petiolate. If petiolate, then the petioles (bladeless portion only) are nearly always shorter than the blade, except in Saintpauliopsis and at least one species of Staurogyne (S. chapaensis), in which the petioles are conspicuously longer than the blades.
Leaf variation is particularly evident in Elytraria. In addition to variation in disposition and arrangement as noted above, length of leaf blades in the genus varies from 4 mm (E. filicaulis) to 310 mm (E. caroliniensis) and the margin varies from entire to sinuate to pinnatisect. Some of the variation in shape, size, and margin among leaves of E. acaulis from India and Sri Lanka is shown in Fig. 2.
Apical/aerial whorls or clusters of leaves may be synapomorphic for some species within Elytraria, but phylogenetic patterns for foliar characteristics are otherwise unclear.

Inflorescences
Inflorescences of Acanthaceae are often complex or highly modified. The basic unit of inflorescences in Nelsonioideae, as in most other Acanthaceae, is a dichasium. The dichasial nature is reflected by the paired bracteoles that subtend each flower. Throughout the subfamily the dichasium is modified by reduction to a single flower. Dichasia of Nelsonia have undergone further reduction by the loss of both bracteoles (although they are very rarely [teratologically?] present below some flowers). Dichasia may be sessile or pedunculate; flowers may be sessile or pedicellate. The dichasia sometimes occur in leaf axils, but more commonly they are subtended by a bract and grouped into sessile to pedunculate spikes (i.e., both dichasia and flowers sessile to subsessile), racemes (i.e., dichasia sessile to subsessile and flowers pedicellate), or thyrses (i.e., dichasia pedunculate and flowers sessile or pedicellate). Each of the spikes, racemes, and thyrses are uncommonly branched to form a panicle. Arrangement of bracts varies from alternate (spirally arranged) in all genera to sometimes subopposite in Anisosepalum to sometimes opposite in Staurogyne.
Unlike variation in plant habit and leaf disposition, inflorescence traits show considerable phylogenetic pattern. In addition to the synapomorphic absence of bracteoles in Nelsonia: 1) scales on inflorescence peduncles are synapomorphic for Elytraria; 2) bracts with paired, subapical, winglike teeth are autapomorphic for E. imbricata; 3) adnation of bracts to dichasial peduncles may be synapomorphic for Anisosepalum, Saintpauliopsis, and Staurogyne (although this trait is difficult to assess owing to the absence of dichasial peduncles and pedicels in the spicate inflorescences of Elytraria and Nelsonia); and 4) adnation of bracteoles to the floral receptacle and calyx tube may be synapomorphic for Saintpauliopsis + Anisosepalum.

Flowers
As in other major lineages of Acanthaceae, floral diversity among Nelsonioideae is particularly evident (Fig. 3). The calyx varies from deeply four-to five-parted. Although calyces of some species of Staurogyne have five homomorphic lobes, those of most species are conspicuously heteromorphically lobed (1 + 2 + 2). The posterior lobe is often the largest. The two lateral lobes are often the smallest, internal to the posterior and anterior lobes, and obscured by the adjacent bracteoles (when present). In most plants, the anterior lobes are connate to a greater extent than the other calyx lobes; more rarely they are completely fused into a single lobe or divided nearly to the base. In Elytraria, the anterior lobes (irrespective of the degree of fusion) show a conspicuous constriction proximally.
Corollas of all Nelsonioideae appear to share a unique, putatively synapomorphic aestivation pattern, descendingcochlear, with the corolla lobes arranged in bud such that the lower-central lobe is innermost (overlapped on each side by the lateral lobes of the lower lip) and the two lobes of the upper lip are outermost (with one overlapping the other, and each overlapping the lateral lobes of the lower lip; see McDade et al. 2012: Fig. 1A-D). We observed this pattern in buds representing each genus of the subfamily. The corolla tube varies from subcylindric to funnelform and is sometimes divisible into a narrowly cylindric proximal portion and an expanded (6 triangular) throat. Much of the floral diversity among Nelsonioideae results from variation in the orientation and form of the limb of the corolla. The limb is usually strongly zygomorphic, but is nearly actinomorphic in some species (e.g., Elytraria caroliniensis; Fig. 3B). It consists of a bilobate upper lip and a trilobate lower lip. The lips may project forward (in line with the tube) or be reflexed at angles to 90u with respect to the tube. Colored markings sometimes occur on some portion of-or throughout-the limb. The variation in size, shape, and color of corollas undoubtedly reflects adaptations to diverse pollinators.  noted two groups of species of Staurogyne based on floral morphology and suggested that these corresponded to melitophily and ornithophily. Although she did not provide evidence of visitation to these flowers by bees or hummingbirds, we agree with her assessments based on floral morphology.
Variation in features of the androecium provide important diagnostic characters for distinguishing taxa of Nelsonioideae, but few synapomorphic traits are evident. Two stamens are present in Nelsonia, most Elytraria, and a few species of Staurogyne. Four stamens characterize Anisosepalum, Malagasy species of Elytraria, Saintpauliopsis, and most species of Staurogyne. Short and usually inconspicuous staminodes have been noted in all genera except Nelsonia. Although up to 3 staminodes have been reported in species of Nelsonioideae, usually only a single staminode (in posterior position) is present. Anthers are bithecous with the thecae equally inserted on the filament in all genera. The connective of the filament is sometimes extended beyond the anthers and appears as an apical appendage (e.g., in some Elytraria from the Old World). The thecae are glabrous in all genera except Anisosepalum and some Staurogyne, in which they are pubescent with eglandular and/or glandular trichomes. The occasional presence of widely divergent anther thecae (i.e., forming a right angle with the filament/connective so that the pair is horizontally positioned with the apex of each theca adjacent, i.e., with stamen Tshaped), as in some Nelsonia and Staurogyne, is not otherwise common among Acanthaceae. In some Staurogyne (e.g., S. capitata and S. macrobotrya) the thecae are apparently divergent nearly 180u so that they appear upside down (i.e., with stamen Y-shaped). Basal or subbasal appendages are found in at least some species of each genus of Nelsonioideae except . Appendages are often flaplike and appear to be associated with dehiscence. Appendages in Saintpauliopsis differ from those in other genera by being bifurcate, a probable autapomorphy for the genus. Dehiscence of the anthers appears to be nototribic (i.e., toward the lower lip) in all genera except Nelsonia, in which it is pleurotribic (i.e., toward each other).
The gynoecium consists of a cylindric to conic ovary with a terminal, filiform style bearing an apical, 6 two-parted stigma. Manifestations of the stigma, which can be difficult to observe in some dried and pressed specimens, offer important diagnostic characters among Nelsonioideae. Variation in stigma form for the subfamily was illustrated by Hossain (2004). Stigmas vary from (equally to) subequally to unequally bilobed, or rarely crateriform (Fig. 4D). In all species of Anisosepalum the longer of the unequal lobes is equally bifurcate, a probable synapomorphy for the genus although similar bifurcation of stigma lobe(s) occurs in some Nelsonia and Staurogyne. Stigmas of Elytraria are remarkably distinctive. They consist of a broad, flattened lobe that folds over the anthers, rapidly unfolds when touched, and slowly refolds over several minutes. These touch-sensitive stigmas appear to play a role in pollination, as they are located at the mouth of the corolla or in the corolla tube, and must be touched before the pollen from their flower is revealed. A minute and inconspicuous second lobe is often evident near the base of the broad lobe on stigmas of Elytraria. These traits of the stigma provide clear synapomorphies for Elytraria.

Pollen
Palynological characters have been widely employed in classification of Acanthaceae since the late 19 th century (e.g., Radlkofer 1883; Lindau 1895); indeed, the family apparently exhibits more diversity in pollen morphology than any other family of plants (Lindau 1895;Raj 1961). Phylogenetic signal at varying taxonomic levels has been associated with pollen sculptural characters of Acanthaceae (e.g., Scotland 1993;Scotland and Vollesen 2000;McDade et al. 2000;Manktelow et al. 2001;Kiel et al. 2006;Daniel et al. 2008). Published studies comparing pollen from all currently treated genera of Nelsonioideae are lacking.
We sampled pollen of 28 species of Nelsonioideae as follows (see Appendix I): Anisosepalum (3), Elytraria (13), Nelsonia (2), Saintpauliopsis (1), and Staurogyne (9). Size, shape, and sculpturing of grains were observed in non-acetolyzed samples of dry pollen using scanning electron and some light microscopy. Additional data have been derived from Raj (1961Raj ( , 1973, Hossain (1971), Scotland (1990), and. Descriptive terminology for pollen generally follows that of Walker and Doyle (1975), with additional insights from Hesse et al. (2009). Results of our observations are provided in Appendix 1, summarized for the subfamily here, and summarized for each genus in the accounts below.
Pollen of Nelsonioideae  varies in shape from oblate spheroidal to spherical to perprolate (P:E 5 0. 82-2.43) in equatorial views and from round to triangular (planaperturate) in polar view. Variation in size encompasses three size classes, small to large. The polar axis varies from 13-58 mm, and the equatorial axis varies from 11-36 mm. Based on sampling to date, the smallest known grains among Nelsonioideae are in several species of Staurogyne (e.g., S. repens; P 5 13-15 mm, E 5 15-18 mm;; Elytraria caroliniensis has the largest grains (P 5 56-58 mm, E 5 28-36 mm).
All grains are triaperturate. The interapertural exine is (microreticulate to) reticulate, but in some grains (nonacetolyzed) it appears 6 psilate to microfoveolate to foveolate. The muri of the reticulum vary from psilate to microverrucate. Apertures of Nelsonioideae consist of elongate colpi, which may or may not contain a centrally located endoaperture (os). In a developmental study, Johri and Singh (1959: 233) indicated the presence of ''three germ pores'' each situated in Revision of Nelsonioideae a colpus in young pollen grains of Elytraria acaulis. Using light microscopy, Raj (1961) determined that pollen of Elytraria (1 sp.), Nelsonia (1 sp.), and Staurogyne (3 spp.) was tricolpate. In a subsequent examination of additional species (Raj 1973: 96), S. spatulata (as S. glauca) was described as tricolpate, but with ''indication of a faint os at each aperture,'' and E. acaulis was described as tricolpate. Based on acetolyzed grains, Hossain (1971) noted that Elytraria (including E. acaulis), Saintpau-   liopsis, and Gynocraterium have tricolpate pollen whereas the other genera of Nelsonioideae also possess either some-or clear evidence of-endoapertures. He concluded that pollen of Nelsonioideae is basically tricolpate with a trend to tricolporate (via ''tricolporoidate'') grains in several genera. Scotland (1990) contended that in Nelsonioideae colpate pollen was restricted to Elytraria. He characterized pollen of three species of Elytraria as tricolpate, E. acaulis as tricolporate (but with the endoapertures often indistinct with light microscopy), Nelsonia canescens and Saintpauliopsis lebrunii as tricolporate, VOLUME 32, NUMBER 1 Revision of Nelsonioideae and 17 species of Staurogyne (including Gynocraterium macrobotryum) from both the Old World and the New World as tricolporate (but with endoapertures often indistinct). Indeed, the indistinctness of endoapertures had led Raj (1961) to describe some of the same species as tricolpate. Twenty-seven Neotropical species of Staurogyne were characterized as tricolporate Braz and Monteiro 2011), and endoapertures are evident in most of the images provided for these taxa by these authors. Contradictory reports for the type of apertures (colpi vs. colpori) among taxa of Nelsonioideae undoubtedly reflect 1) the difficulty of seeing endoapertures in grains where the flanks of the colpi are ''closed'' and do not reveal the interior contents (e.g., Fig. 5G, 6A,E,G, 7B,C,E), and/or 2) their rather weak manifestation, even in ''open'' colpi compared to most other Acanthaceae with compound apertures (at least in mature grains; e.g., Fig. 5A-F, 7H,I). It is evident from the studies noted above, which have used various techniques (e.g., acetolyzed and non-acetolyzed pollen, whole grains and sectioned grains) and both light and scanning electron microscopy, that acetolysis does not always help to reveal the presence or absence of endoapertures in Nelsonioideae. It is possible that all Nelsonioideae have endoapertures, but that these are cryptic (or become so in later stages of development) in some taxa. Our observations, using non-acetolyzed pollen and both light and scanning electron microscopy, largely agree with those of Hossain (1971). Thus, endoapertures among Nelsonioideae vary from absent (or imperceptible) to inconspicuous to conspicuous.
The apparent taxonomic pattern of aperture type among genera of Nelsonioideae (including colpate and colporate pollen, which also both occur among other Acanthaceae and related families) does not appear to be phylogenetically informative. However, the lack of subsidiary apertures (e.g., pseudocolpi) and other modifications (e.g., bireticulate exine, bifurcate colpi, sexine lips) implicate Nelsonioideae (as well as Thunbergioideae, Avicennia, and Acantheae) as likely more basal in the family. This implication has been confirmed by several molecular phylogenetic analyses (e.g., McDade et al. 2012). Johri and Singh (1959) indicated that pollen of Elytraria acaulis used in their developmental studies was syncolpate. Pollen with colpi fused at one or both poles was not encountered in our studies of Nelsonioideae; however, the syncolpate condition is sometimes variable within species of Acanthaceae (e.g., Aphelandra; McDade 1984; Daniel 1991).
Some variation in pollen sculpturing among Nelsonioideae appears to have phylogenetic and/or taxonomic significance. Pollen of all species of Anisosepalum differs from that of other genera of Nelsonioideae in two features: conspicuous ridges near margins of colpi ( Fig. 5A-F), and microreticulate (i.e., lumina ,1 mm in diameter) exine ( Fig. 8A-C). In Elytraria caroliniensis the reticulum of the exine has much broader muri ( Fig. 6C,D, 8E) than encountered elsewhere in the subfamily. Based on this feature and its large size, pollen of E. caroliniensis is the most distinctive in the genus. Microverrucate muri (Fig. 8D,E,I) occur only in Saintpauliopsis and in Elytraria from the New World. Although microverrucate muri are present in all pollen samples of Elytraria from the New World examined to date, pollen has yet to be examined for any species from the West Indies (flowers for most species there remain unknown). All species of Elytraria from the Old World have psilate muri.
Because phylogenetic work to date indicates that New World species of Elytraria (inclusive of the one West Indian species sampled) are monophyletic, we predict that West Indian species will also have pollen with microverrucate muri.

Fruits
Fruits of Nelsonioideae, like most other Acanthaceae, consist of indurate and loculicidal capsules that dehisce explosively into two valves. They show only minor diversity of size and shape among or within genera, unlike other major lineages of Acanthaceae that encompass considerably more variation. Nelsonioid capsules are estipitate, usually ovoid to subconic to linear-ellipsoid in shape, fertile from the base, and sterile apically ( Fig. 9). They lack the indurate and hooklike retinacula subtending the seeds that are synapomorphic for subfamily Acanthoideae. The presence of papilliform retinacula has often been noted for genera of Nelsonioideae. This presumably refers to the discolored regions of septum where a papilliform connection (to 0.1 mm long) to the seed sometimes remains ( Fig. 9A-D).  also noted the presence of non-indurate and caducous retinacula in Anisosepalum, but he did not describe or illustrate these. In Anisosepalum alboviolaceum, we observed coarse, threadlike connections (0.1-0.4 mm long) from discolored regions of septum to ovules and seeds (Fig. 9E). Whether these structures are homologous to the retinacula encountered in Acanthoideae remains to be determined. Hossain (1971Hossain ( , 2004 noted the rare presence of tardily dehiscent or indehiscent capsules in some Staurogyne, and he noted that this characteristic had been the basis for the African genus Staurogynopsis. Champluvier (1991) described the African species of Staurogyne section Zenkerina as having capsules with a membranous (vs. indurate in other species) wall and both delayed and non-explosive dehiscence. Tardily dehiscent or indehiscent capsules are also known elsewhere in the family in genera with otherwise regularly dehiscent capsules (e.g., Justicia; Hedrén 1989), and likely represent a specialization that has occurred numerous times in the family.

Seeds, Hygroscopic Trichomes, and Endosperm
Ovules and seeds among Nelsonioideae tend to be more numerous than elsewhere in the family. The number of seeds that develop per capsule varies from six (e.g., Elytraria spp., Staurogyne carvalhoi) to 68 (e.g., Staurogyne spp.). Mature seeds are generally smaller than in other Acanthaceae. The longest axis varies from 0.3 to 2 mm, but in most species is less than 1 mm. Anisosepalum has the largest seeds, with the longest axis varying from 1.1 to 2 mm. Dimensions of seeds that have been expelled from the mature capsule can be difficult to attribute to length, width, or height because the hylar scar is not always evident and the seeds are usually irregular in shape (frequently somewhat blocky to oblong to ellipsoid to subhemispheric to cochlear). However, the hylar scar forms a conspicuous depression in Anisosepalum and to a lesser extent in Nelsonia (Fig. 4E). The surface of seeds varies from smooth to reticulate to foveolate, and sometimes includes minute protrusions (e.g., verrucae, gemmae, baculae, etc.; Fig. 10 -12). The presence or absence of seminal trichomes was found to be useful in characterizing the five genera of Nelsonioideae. They are apparently universal in all genera except Elytraria and Anisosepalum, in which they do not occur.
Seminal trichomes of Nelsonioideae are simple or usually branched; the number of branches per trichome can vary on a seed. The trichomes are also hygroscopic.
Hygroscopic trichomes in Acanthaceae are usually appressed to the seed surface and expand and/or become erect on being wetted with water; they often discharge mucilage. Such trichomes have long been known among various Acanthaceae (Kippist 1845). They occur on seeds of some taxa in two of the three currently recognized subfamilies (Nelsonioideae and Acanthoideae) and in six of the seven tribes of Acanthoideae: Ruellieae (Tripp et al. 2013), Justicieae (e.g., Daniel and Figueiredo 2009), Barlerieae (Manktelow et al. 2001;McDade et al. 2008), Acantheae McDade et al. 2005), Whitfieldieae (Manktelow et al. 2001;McDade et al. 2008), and Neuracantheae (Bidgood and Brummitt 1998;McDade et al. 2008). Whether hygroscopic trichomes in all of these taxa are homologous remains to be determined. To our knowledge, hygroscopic trichomes are not known to occur on seeds of Avicennia, Thunbergioideae, or Acanthoideae: Andrographideae.
Hygroscopic trichomes on seeds of Nelsonioideae were illustrated by Oersted (1855) and Lindau (1895). In this subfamily apically hooked, double-hooked (i.e., anchor shaped), or multi-branched trichomes that lack copious mucilage are appressed to the dry seed surface (Fig. 9F,I, 11G-I, 12); these usually become erect (and clearly visible) upon hydration (Fig. 9G,H). Kippist (1845: 73) noted that whereas trichomes of Nelsonia ''expand very slowly when wetted,'' in two species now treated in Staurogyne, a similar reaction to water was inconclusive ''owing to [the trichomes'] extreme minuteness, and the very slight action which water has upon them.'' Our results (Appendix 2) were similar. Trichomes Less dramatic reactions observed in other samples of Nelsonia, Saintpauliopsis, and Staurogyne included: some or most of the trichomes expanded, but the trichomes are short (,0.05 mm long, e.g., Staurogyne obtusa; Fig. 9H) and inconspicuous, and the reaction was not immediate (e.g., both samples of Saintpauliopsis lebrunii); only some of the trichomes became erect after a minute or more (e.g., some Nelsonia canescens); and no apparent reaction of the trichomes within three minutes (e.g., some seeds of Staurogyne spp.). Thus not all of the seminal trichomes were always reactive. Although hygroscopy was observed in all species of Staurogyne tested, all trichomes on some, but not all, seeds showed no reactivity. Possible causes of non-reactivity include: age of seed, method of preservation of seed, immaturity of seed, and innate lack of reactivity in some trichomes. Bremekamp (1953) noted well developed endosperm in Nelsonioideae, and it was largely based on this trait that he considered these plants more closely related to Scrophulariaceae than Acanthaceae (Bremekamp 1955). Hossain (1971) characterized endosperm of Nelsonioideae as usually persistent, oily, and alveolate. Borg et al. (2008) indicated that the presence of persistent (vs. non-persistent) endosperm was one of the characteristics by which the subfamily differs from other  Acanthaceae. Several species of Andrographis (Acanthoideae: Andrographideae) have both persistent and ruminate endosperm, like that described for species of Elytraria and Nelsonia (Mohan Ram and Wadhi 1965), and the presence of one or more layers of persistent endosperm in mature seeds was noted for diverse taxa throughout the family by Mohan Ram and Wadhi (1964). However, as noted by Scotland and Vollesen (2000), this trait remains poorly documented in the family and merits further study. CHROMOSOME NUMBERS Knowledge of chromosome numbers has been helpful in understanding the systematics, evolution, and biogeography of some taxa of Acanthaceae (e.g., Daniel 2000Daniel , 2006McDade et al. 2000McDade et al. , 2005. To date, chromosome numbers have been reported for seven species of Elytraria (Appendix 3). Among them, the three Mexican taxa sampled have relatively low (presumably diploid) numbers of n 5 (11) 12 whereas taxa from the southeastern United States and the Old World have higher (presumably polyploid) numbers of n 5 (17) 19, 22, 23, and 25. The only other genus of Nelsonioideae for which counts have been reported is Nelsonia (Appendix 3), with all counts (n 5 14, 16-18) presumably attributable to N. canescens. It remains to be seen how useful chromosome data will be for understanding patterns of relationships among these taxa, but the diversity of numbers reported for the small sample of Elytraria is encouraging. Additional counts for species of Elytraria and Nelsonia, and initial counts for all other genera of Nelsonioideae are highly desirable.

DISTRIBUTIONS, BIOTIC COMMUNITIES, AND BIOGEOGRAPHY
The distribution of Nelsonioideae is nearly pantropical with incursions into temperate regions in North America (northern Mexico, southern United States to ca. lat. 33uN), South America (southeastern Brazil), Africa/Madagascar (northern South Africa to ca. lat. 27.5uS, southern Madagascar), and Asia (China, India, Japan-southern Ryukyu Islands, Nepal). The subfamily does not appear to be present on tropical Pacific islands located east of the Solomon Islands. All genera occur in Africa, with Anisosepalum restricted to that continent and Saintpauliopsis occurring only in Africa and Madagascar. Three genera (Elytraria, Nelsonia, Staurogyne) also occur in Asia, with Nelsonia and Staurogyne also distributed eastward to Australia. Two genera (Elytraria and Staurogyne) are native to-and have radiated in-the New World. The native range of Nelsonia is not known with certainty; the genus may not be native to the New World, but the non-native range of N. canescens there appears to be expanding (cf. Franck and Daniel 2012).
A comparative study of biotic communities in which Nelsonioideae occur has not been attempted based on the information available in floristic accounts and on herbarium specimens. However, it is clear from those sources and from our own field observations that some species occur in very wet communities (e.g., wet evergreen forest) and others occur in dry communities (e.g., tropical deciduous forest). Species of Anisosepalum and Saintpauliopsis appear to occur only in wet evergreen forests. Plants treated herein as Nelsonia canescens occur in a wide range of biotic communities from wet evergreen forest (in western Africa) to grasslands (in Southern Africa) to arid scrub (in southern Madagascar). Most species of Staurogyne appear to occur in moist to wet communities (e.g., all African species occur in wet evergreen forest), but Mexican plants of S. miqueliana (Daniel and Lott 1993; as S. agrestis) were collected along a dry streambed in a region of dry forest (tropical subdeciduous forest). Elytraria contains species that are restricted to wet evergreen forest (e.g., E. marginata) and others that occur only in seasonally arid tropical deciduous forest (e.g., E. mexicana). The widespread E. imbricata occurs in diverse biotic communities from desert to mesophytic montane forest and at elevations from sea level to 2200 m.
Biogeographic analyses of Elytraria (Wenk and Daniel 2009;McDade et al. 2012) optimized Africa as the area of origin for the genus with dispersals to Madagascar, the Indian subcontinent, and the New World. At least three subsequent dispersal events within the New World could account for the current distribution of species of Elytraria there. Wenk and Daniel (2009) proposed rafting as the mode of dispersal for seeds or plants of the genus between landmasses. Dispersal by rafting may be most plausible for genera that lack the apically hooked and hygroscopic trichomes (e.g., Elytraria), which possibly play a role in zoochoric dispersal. Saintpauliopsis + Anisosepalum retain the symplesiomorphic African distribution, with dispersal to Madagascar within Saintpauliopsis lebrunii.
The richest genus of Nelsonioideae, Staurogyne, apparently dispersed to the New World early in its evolutionary history as the New World clade is sister to a clade comprising all other species. A subsequent dispersal from Africa to Asia resulted in a major radiation that is today represented on the southeastern mainland of that continent and islands to the east. Interestingly, only five species are present in Africa today, far fewer than in the New World or in Asia. Whether this represents a decrease in richness over time due to climatic changes (e.g., increasing aridity) in Africa or relatively little speciation during its history on that continent remains an interesting question.
There have been at least three colonizations of Madagascar by Nelsonioideae. Presumably because of Madagascar's lengthy isolation from Africa (separation of Indo-Madagascar began ca. 165 mybp; Krause 2003), there are relatively few species of Acanthaceae common to both landmasses (Benoist 1967;Daniel unpubl. data). It is therefore of interest that whereas Elytraria is represented on the island by two very distinctive endemic species, the other genera of Nelsonioideae are each represented by a species that also occurs in Africa: Nelsonia canescens and Saintpauliopsis lebrunii. We hypothesize that future phylogenetic work to date these dispersal events will show that Elytraria arrived considerably earlier that the two other Nelsonioideae.

FUTURE STUDIES
With  account of the American species and  treatment of the African species of Staurogyne, a modern revision of the Asian species of that genus remains the most urgent taxonomic priority among Nelsonioideae. Bremekamp's (1955) detailed study of the Malesian species serves as a useful starting point in this regard. Additional molecular studies of Nelsonia on a worldwide basis will likely be useful in resolving both the number and rank of taxa that would be appropriate to recognize in that genus.
Such studies linked to a time-calibrated phylogeny should determine whether putatively native populations of the genus in the New World are indeed pre-Columbian. Collections of Elytraria with flowers and fruits from Cuba and Haiti are much desired to better resolve the taxonomy of the genus in the West Indies. TAXONOMY The following account is intended to delimit monophyletic genera of nelsonioids, to characterize each one, and to tabulate currently recognized species. It provides the known geographic distribution (by country), synonyms, and relevant taxonomic or nomenclatural notes for each genus and species. NELSONIOIDEAE Pfeiff., Nomencl. Bot. 1 (1): 10 (1871)  Annual or perennial, acaulescent to caulescent, and terrestrial (to epiphytic or epipetric) herbs or shrubs, cystoliths absent. Leaves opposite or whorled or alternate, sometimes clustered at ground level or at apex of branches or along stems, sessile to petiolate, margin of blade entire to sinuate-crenate to shallowly dentate to pinnately lobed. Inflorescence of dichasia in leaf axils or more commonly consisting of sessile or pedunculate, axillary or terminal dichasiate spikes or racemes or thyrses (or if branched then panicles of these), peduncles naked or with alternate (spirally disposed) clasping scales; dichasia opposite or alternate (sometimes spirally disposed), sessile or pedunculate, 1-flowered, subtended by a (leaf or) bract. Bracts subfoliose or usually greatly reduced in size relative to leaves, not overlapping to densely imbricate, borne along rachis or sometimes adnate at base to dichasial peduncle and becoming free along peduncle. Flowers sessile to pedicellate, homostylous, flower or flower + pedicel subtended by paired bracteoles (except in most Nelsonia). Bracteoles of a pair homomorphic, sometimes with basal portion partially adnate to calyx tube. Calyx deeply 4-5-parted, lobes heteromorphic (1 + 2 + 2) or rarely subequal, posterior lobe often largest, lateral lobes usually shortest, interior to posterior and anterior lobes, and often obscured by bracteoles, anterior lobes sometimes longest and sometimes connate to a greater extent than other lobes. Corolla entirely white or variously colored, tube subcylindric to funnelform, narrow proximal portion 6 cylindric, throat (if present) expanded toward mouth of corolla, limb (subactinomorphic to) strongly zygomorphic (2labiate), upper lip entire or 2-lobed, lower lip 3-lobed, central lobe usually largest, corolla lobes with descending cochlear aestivation. Stamens 2 or 4, if 4 then didynamous (or if 6 equal in length then inserted at different heights), included in or exserted from mouth of corolla, anthers not surpassing lips or extended well beyond lips, 2-thecous, thecae dehiscing toward lower lip (i.e., flower nototribic) or toward each other (i.e., flower pleurotribic), those of a pair equally inserted, with or without a basal appendage; pollen oblate spheroidal to spherical to perprolate (P:E 5 0. 82-2.43), round to triangular in polar view, 3-colpate (endoapertures, if present, not evident) to 3-colporoidate (endoapertures evident but indistinct) to 3colporate (endoapertures distinct), exine reticulate (sometimes appearing foveolate in non-acetolyzed grains), muri smooth or microverrucate; staminodes 0-2 (-3). Style included in or exserted from mouth of corolla. Capsule estipitate, ovoid to subconic to linear-ellipsoid, lacking retinacula. Seeds (6-) 12-68 per capsule, variable in shape (often 6 blocky or irregularly shaped), hygroscopic trichomes present or absent, endosperm present.
We recognize five genera with 172 species in the subfamily. They are nearly pantropical in distribution, and occur to a lesser extent in temperate regions. All genera occur in Africa; Elytraria, Nelsonia, and Staurogyne are also native to Asia; and at least Elytraria and Staurogyne are native in the New World.
Three species from tropical Africa (Fig. 14) are recognized in this genus. All of them are well collected and morphologically documented. Detailed taxonomic accounts of the genus were provided by  and . The two species initially treated by Hossain (1972: 378) were segregated from Staurogyne based on differences in the calyx (''form of calyx … approaches Saintpauliopsis''), corolla (palate on lower lip), number of ovules (6 to 8 vs. 12 or more), and seeds (with a large hilar excavation and rugose testa, and lacking ''hooks on their testa cells''). We recognize Anisosepalum as morphologically distinct among Nelsonioideae by a unique combination of characters: bracteoles fused to the base of the calyx (like Saintpauliopsis), corollas with a conspicuous palate (likely synapomorphic), thecae with an undivided and flaplike basal appendage (like Nelsonia), seeds lacking hygroscopic trichomes (like Elytraria) and with a conspicuous and deep hylar excavation (likely synapomorphic), and pollen with conspicuous ridges near the colpal margins (synapomorphic).
Currently Recognized Species of Anisosepalum   recognized two subspecies, alboviolaceum and gracilius (Heine) Champluvier, based on habit and pubescence of the external surface of the corolla. Within subsp. alboviolaceum she treated five informal groups based on geographic distribution and differences in shape, size, and pubescence of the corolla.  noted variation in size of the corollas in different parts of the geographic range of the species, but he did not recognize formal infraspecific taxa; he also did not specifically include subsp. gracilius as a synonym. However, he did include the distribution of subsp. gracilius within the geographic range of the single taxon recognized.  Staurogyne humbertii Mildbr. Champluvier (1991) recognized two subspecies: humbertii and zambiense Champluvier. These were based on position of the ring of trichomes inside the corolla tube and the width of the corolla tube below the lips. Vollesen ( , 2013 maintained these subspecies and noted that subsp. zambiense has a longer corolla tube with the ring of hairs on its internal surface located more distally. Based on our observations, the subspecies appear very similar (the differences being relatively minor and not mutually exclusive), but their geographic ranges apparently do not overlap.

Anisosepalum lewallei P. Bamps (Burundi, Tanzania)
This is a highly distinctive species with generally ternate leaves. Although opposite leaves occur, at least some nodes (usually most) per shoot bear three leaves. Corollas of this species (3-3.9 cm long; Fig. 13D) are the largest in the genus.   Acaulescent to caulescent, erect to spreading annual or perennial herbs to shrubs to 0.5 (-1) m tall. Young stems subterete to 3-angulate to subquadrate, sometimes 6 flat on drying, glabrous, pubescent with eglandular trichomes, or glabrate. Leaves alternate or whorled, 6 diffuse along stems or borne in basal rosettes (usually from a subterranean caudex or rhizome) or aerial whorls or aerial clusters (up to 11 leaves per cluster), sessile to petiolate, petiole (if present) usually shorter than blade, margin of blade entire to crenate to pinnatifid. Inflorescence of (sessile to) pedunculate axillary and terminal densely bracteate spikes, peduncles (if present) covered with imbricate or remote coriaceous clasping scales, fertile portion of spike cylindric, 1.8-17 mm in diameter (excluding corollas) near midpoint, simple or sometimes branched, rachis not or only partially visible; dichasia alternate (spirally disposed), sessile. Bracts alternate (spirally disposed), imbricate, green or partially hyaline, not fused to other structures, coriaceous to sclerophyllous, lanceolate to ovate to broadly ovate to elliptic to hour-glass shaped to obovate, 2.5-11 mm long, 1-5.8 mm wide, 1-or 3-veined or veins not evident, sometimes apically toothed and/or winged. Bracteoles borne at base of (but not adnate to) flower, positioned near edges of posterior calyx lobe and 6 conduplicate there, often mostly hyaline, narrowly elliptic to linear to lanceolate to lance-lunate to subulate, 1.6-7.5 mm long, 0.2-1.7 mm wide. Flowers sessile. Calyx usually appearing deeply 4-lobed, mostly hyaline, 1.8-8.5 mm long, lobes heteromorphic, 6 equal in length, posterior lobe 1.8-7.5 mm long, lateral lobes 1.7-7 mm long, anterior lobe 1.9-8 mm long, 2-dentate to 6 deeply 2-cleft from apex, all lobes obscurely veined abaxially. Corolla pinkish or blue or yellow or entirely white or dark purple and white, sometimes with colored markings near mouth, 3-17 mm long, externally glabrous or pubescent, tube cylindric or slightly expanded near mouth, throat indistinct or evident only near mouth, limb (subactinomorphic to) 2-labiate, upper lip 2-lobed, lower lip lacking a bullate palate, corolla lobes often apically divided or 2-cleft. Stamens 2 (or 4 in species native to Madagascar), inserted at/near apex of corolla tube or near midpoint of tube, anthers included in corolla tube or partially exserted from mouth of corolla, not extending beyond lips of corolla, thecae (covered by folded stigma during anthesis) dehiscing toward lower lip (i.e., flower nototribic), oblong to broadly ellipsoid, 0.3-1.7 mm long, those of a pair parallel, equal to subequal in size, glabrous, lacking basal appendages, connective sometimes with an apical appendage (in some Old World spp.); staminodes 0-2, minute; pollen suboblate to spherical to perprolate (P:E 5 0.82-2.43; polar axis 25-58 mm, equatorial axis 14-36 mm), 3-colpate to 3-colporoidate, exine reticulate (sometimes appearing 6 foveolate in non-acetolyzed grains), muri psilate or microverrucate. Style included in corolla tube or if exserted from mouth of corolla then not extending beyond lips of corolla, stigma folded over anthers during anthesis and straightening when touched (touch-sensitive) and gradually refolding, appearing non-lobed but usually with a minute and inconspicuous lobe (to 0.3 mm long) borne on an expanded, flat, subelliptic to subspatulate lobe (rarely subcrateriform), 0.4-2.5 mm long, 0.2-1.2 mm wide. Capsule conic to ovoid to linear-ellipsoid, sometimes irregularly constricted proximally, 2.1-9 mm long, glabrous (rarely inconspicuously glandular punctate, but lacking elongate trichomes). Seeds to 26 per capsule, irregularly shaped (often blocky or reniform or ellipsoid), longest axis 0.3-1.7 mm, shortest axis 0.3-1.5 mm, surface (smooth to) lumpy-to rugose-to foveolate-reticulate, microverrucate to microbaculate and with smaller rounded to pointed protrusions that sometimes form chains or a microreticulum, lacking trichomes; x 5 11 or 12?; (Fig. 15).
The genus consists of 21 species occurring in the tropics, subtropics, and warm deserts of both the Old World and the New World (Fig. 16). The majority of species are American (14), but species also occur in Africa (5), Madagascar (2), and the Indian subcontinent (1). Except for the naturalized presence of weedy Elytraria imbricata in Madagascar, southeastern Asia, and Malesia, there are no species common to the Old World and the New World. North American and African species are well collected and fully documented morphologically (e.g., Morton 1956;Dokosi 1970Dokosi , 1971Dokosi , 1979Daniel and Acosta C. 2003;Daniel in press). Species endemic to South America and Madagascar are poorly collected but reasonably well known (e.g., Benoist 1967;Wenk 2008). The seven species endemic to the West Indies remain very poorly collected, morphologically documented, and taxonomically resolved; indeed, corollas remain unknown for most of those species (e.g., Borhidi and Muñ iz 1978). A monograph of the entire genus is currently in preparation.  recognized two subgenera: Tetrandra E. Hossain consisting of the two species endemic to Madagascar (characterized by woody habit, whorled leaves, and four stamens), and Elytraria consisting of all other species (characterized by mostly herbaceous habit; alternate, whorled, or clustered leaves; and two stamens). Molecular phylogenetic results (Wenk and Daniel 2009;McDade et al. 2012) reveal that the subgenera are not monophyletic.
Elytraria is distinctive among Nelsonioideae by having peduncles (absent only in E. madagascariensis) covered with alternate (spirally arranged) scales, coriaceous to sclerophyllous bracts, and touch-sensitive stigmas. All three traits appear to be synapomorphic for the genus. Another significant character of Elytraria is the absence of minute, hooklike, and hygroscopic trichomes on its seeds (shared with Anisosepalum). Variation in several morphological attributes is notable for the genus. Habit varies from acaulescent herbs from a woody caudex or rhizome (most species) to monocaulous or branched herbs (e.g., E. marginata, E. imbricata) to shrubs (e.g., E. nodosa). Most species have either a taproot or fibrous roots, but one (E. tuberosa) has fibrous roots that bear elongate and conspicuously swollen tubers. Tuberous roots are otherwise unknown among Nelsonioideae, but they are known elsewhere among Acanthaceae (e.g., Ruellia tuberosa). Leaf margin varies (sometimes intraspecifically) from entire to crenate to lobed to subpinnatisect. Floral diversity in Elytraria encompasses size, color, and form of the limb of corollas. The West Indian endemic, E. shaferi, has the smallest known corollas (3 to 3.7 mm long), and the continental American species E. caroliniensis and E. mexicana have the largest (up to 17 mm long). Although the color(s) of corollas for several species in South America and the West Indies remains unknown, so far as is known, all species endemic to the Old Word (with possible exception of E. madagascariensis, which is reported to have white-pink corollas fide Benoist 1967), South America, and West Indies have white to cream corollas. Among North American (United States, Mexico, and Central America) species, corolla color varies from white (E. caroliniensis) to pink (E. bromoides) to blue (E. imbricata) to yellow (E. macrophylla) to white and purple (E. mexicana). Limb form varies from bilabiate with lips little opened (e.g., E. marginata) to bilabiate with lips widely spreading (e.g., E. macrophylla) to subactinomorphic (e.g., E. caroliniensis). Androecial diversity in Elytraria is greater than in any other genus of Nelsonioideae (except perhaps Staurogyne in which various numbers of staminodes have been reported). The following combinations of number of stamens and staminodes are represented: two stamens + no staminodes, two stamens + two staminodes, and four stamens + no staminodes.

Currently Recognized Species of Elytraria
This list is based on Wenk and Daniel (2009) and on a revision of the genus that is currently in preparation. This species, which occurs in subtropical (southern Florida) and temperate regions of the southeastern USA, is the northernmost-occurring species of Nelsonioideae (to ca. 33uN latitude). Its flowers are unusual in their subsalverform shape with a subactinomorphic limb.
Opinion varies as to whether a single variable species (e.g., Hossain 1984;McDade et al. 2012) or several species (e.g., Bremekamp 1964;Morton 1979; should be recognized. Although the genus appears to be native in Africa, Asia, and Australia, it remains unknown whether it is native or introduced in tropical America (Fig. 18). Bremekamp (1955) indicated that Nelsonia was a Paleotropical genus that has spread to the New World in post-Columbian times.  indicated that there are likely five species of Nelsonia, three in Africa (N. canescens, N. gracilis, and N. smithii), one in southern Asia (N. canescens), one in Australia (N. campestris), and two in the New World (N. canescens-introduced and N. pohlii-native). In addition to species that have been described, Champluvier has annotated a large number of specimens at BR as a new species, ''N. feracissima Champl.,'' from Burundi, Cameroon, Congo-Kinshasa, Equatorial Guinea-Bioko, Malawi, Mozambique, Rwanda, and Tanzania. Molecular phylogenetic studies that included plants sampled from multiple continents led McDade et al. (2012) to suggest that only a single species was likely represented. However, these authors did not include N. gracilis, and that species appears rather distinctive morphologically. Major questions that remain to be resolved in this genus include the number of species deserving recognition and whether any of the occurrences in the New World represent native (i.e., pre-Columbian) populations.
Nelsonia exhibits a unique synapomorphy within Nelsonioideae, the absence of bracteoles below the flowers. The rare (teratological?) presence of bracteoles in some Nelsonia (Daniel and Figueiredo 2009) permits recognition of the homology of its flowers to those of the one-flowered dichasial units in other nelsonioids. The inflorescences of the genus (i.e., with peduncles, if present, lacking scales and with dense, cylindric spikes bearing imbricate bracts and small corollas) are also unlike those of other Nelsonioideae. With Staurogyne and Saintpauliopsis, Nelsonia shares the characteristic of seeds bearing hooked or branched hygroscopic trichomes. The species is native to several regions in the Old World (Africa, Asia, Australia), but due to its propensity to spread into disturbed habitats, its overall natural distribution is not known with certainty and may be less extensive than the list of nations, noted above, in which it is currently found. Its numerous occurrences in the New World (e.g., Bolivia, Brazil, Colombia, Costa Rica, El Salvador, French Guiana, Honduras, Mexico, Nicaragua, Panama, Puerto Rico, United States) possibly contain some native populations (e.g., Colombia, where the species was collected near Cartagena in 1801 [without collector at P], and Brazil, where the species was collected in Goiá s as early as 1821 . Map showing the worldwide distribution by country of Nelsonia (some or all of the New World distribution represents naturalized occurrences). VOLUME 32, NUMBER 1 Revision of Nelsonioideae Hilaire cat. num. 766 at K and P]). The species was collected in southern Central America (Costa Rica and Panama) and the West Indies (Puerto Rico) during the 1850s. Other collections from the New World are clearly of recent origin (e.g., Florida in the USA; Franck and Daniel 2012). Both Morton (1979) and Hossain (1984) noted the likely adventive occurrence of N. canescens on many islands in the Pacific. We have not been able to locate records of Nelsonia from Pacific islands (other than New Guinea), nor have such been reported in numerous floras covering the region (e.g., Yuncker 1959;Heine 1976;Smith 1991;Fosberg et al. 1993;Meyer and Lavergne 2004). Hossain (1984) noted considerable variation in habit, leaves, bracts, and pubescence for this species, but he reported insignificant correlations among the major morphological characters. We observed additional variation in the color of corollas as noted on herbarium specimen labels and observed by us in the field or in photographs. Plants may have corollas with the limb entirely white (Australia), white with pink to maroon coloration on the distal portion of the lobes (Africa, America), blue to purple (Africa, America, Asia), purple with dark purple striations on the upper lip (Africa, Asia), and purple with dark purple spots on the lower lip (America; Fig. 3F-I). A similar case among Acanthaceae of a widespread species with multiple color patterns on corollas was noted for Henrya insularis Nees ex Benth. . We also noted variation in the division of the anterior calyx lobe. Most plants have calyces with the anterior lobe shallowly cleft or divided up to M the length of the lobe. In some plants from Australia the anterior lobe is entire (Barker 1986) whereas in others it is divided more than L its length (e.g., Lazarides 9080 at L from Australia: Northern Territory).
Discussions about whether to recognize N. smithii as distinct from N. canescens include those of Morton (1979), Hossain (1984), , Daniel and Figueiredo (2009), Franck and Daniel (2012), and McDade et al. (2012. Observations made on plants occurring in three different habitats in the vicinity of Lagos, Nigeria showed slight differences in characters, but it was not determined whether those differences were genetically fixed or correlated with the different habitats (Hossain and Emumwen 1981). Morton (1979) noted that presumably native plants from Brazil that were described as N. pohlii are intermediate between N. smithii and N. canescens in most of the morphological characters he used to distinguish the two species. Until additional studies provide more convincing insights, Hossain's (1984) broad interpretation of this species is utilized here. Fongod et al. (2010) reported efficacy of N. canescens as a beneficial cover crop (especially in weed suppression) in banana plantations.

Nelsonia gracilis Vollesen (Angola, Malawi, Zambia)
This species of annual duration with sessile to subsessile leaves and bluish flowers appears rather distinctive, but some plants (e.g., Bingham 10092 at K from Zambia) appear to be perennial, and flowers of some collections of N. canescens are also described as ''blue.'' Some apparently annual (or first-year perennial) plants of the latter species (e.g., Henty & Foreman NGF 49370 from Papua New Guinea at L) are similar to N. gracilis with their wiry stems and small, elliptic, and subsessile to short-petiolate leaves.
A single species from tropical Africa and Madagascar (Fig. 20) is recognized in this genus. Plants are often mistaken for Gesneriaceae (indeed, the genus was originally treated in that family ;Staner 1934), and often grow in habitats (e.g., mossy banks) typical of many gesneriads. The species shows similarities to, and has been treated in, Staurogyne (Burtt 1958). Indeed, leaves and inflorescences of Saintpauliopsis lebrunii greatly resemble those of Staurogyne chapaensis from southeastern Asia (although the bracteoles are not fused to the flower in the latter species). If Saintpauliopsis were to be treated in an expanded concept of Staurogyne, Anisosepalum also would have to be included in that genus in order to maintain monophyly of genera. Saintpauliopsis differs from Staurogyne and Anisosepalum by the characters noted in the key above.
In addition to the distinctive habit and leaves of Saintpauliopsis, the inflorescence is unusual among Nelsonioideae. It is sometimes noted to be a raceme. It is not treated here as such because the lateral branches are presumed to be modified dichasia on peduncles. The combination of alternate dichasia (sometimes resulting in a zig-zag rachis), a thin (,0.5 mm in diameter on flattened specimens) and wiry rachis, partial adnation of the bract with the dichasial peduncle and its emergence near the apex of the peduncle on the anterior side (i.e., farthest from rachis) of the dichasium, and partial adnation of the bracteoles to the floral receptacle and calyx tube is unique among Nelsonioideae. According to Dickinson (1978; where Saintpauliopsis is cited as an example), flower-bract associations of this type are examples of cryptic epiphylly. Adnation of bracteoles with the base of the flower also occurs in Anisosepalum, and appears to represent a morphological synapomorphy for the clade consisting of these two genera.
A bifurcate basal appendage on each anther theca was reported by Hossain (2004) and was observed on specimens with visible stamens that we examined. The bifurcate nature of the appendage was not noted by Staner (1934), . Whether it is indeed ubiquitous in plants of the genus or not remains unknown. We found no morphological differences between plants from Madagascar and those from the African continent. Detailed label notes on Perrier de la Bâthie 9257 (P) from Madagascar indicated flowers as having two stamens and two staminodes. It is unknown whether this represents an error of observation (no corollas are extant on the specimen at P) or variation in the androecium of this species. Zenkerina kamerunensis Engler Acaulescent to caulescent, prostrate to decumbent or ascendant to erect annual or perennial herbs or rarely shrubs. Younger stems subterete to subquadrate or becoming 6 flattened on drying, subglabrous or pubescent with eglandular and/or glandular trichomes. Leaves opposite (or distal ones sometimes subopposite or alternate), evenly disposed along stems or in a basal cluster, sessile to petiolate, petiole usually shorter than blade, margin of blade entire to sinuate-crenate or shallowly dentate. Inflorescence of dichasia in leaf axils or usually of pedunculate axillary and/or terminal spikes, racemes, or thyrses, these sometimes branched and forming panicles, fertile portion of inflorescence loose or dense, not cylindric to cylindric, peduncles lacking clasping scales (rarely with a few scattered non-clasping sterile bracts); dichasia opposite or alternate, sessile to pedunculate. Bracts opposite or alternate, imbricate or not, green or otherwise colored, membranaceous, borne along inflorescence rachis or adnate to dichasial peduncle for 11-80 (-100%) the length of the peduncle, subfoliose or triangular to subulate to elliptic to subcircular to obovate-elliptic to oblanceolate, 2-35 mm long, 0.5-11 mm wide, 1-, 3-, 5-, or 7-veined. Bracteoles borne at apex of dichasial peduncle or at base of flower (but not adnate to receptacle or calyx), green or otherwise colored, subulate to narrowly elliptic to elliptic to oblanceolate, 1.5-19 mm long, 0.4-5.7 mm wide. Flowers sessile to pedicellate. Calyx deeply 5-lobed, green or otherwise colored or at least partially hyaline, 3-36 mm long, lobes 6 heteromorphic (1 + 2 + 2; rarely subequal), posterior lobe 3-35 mm long, 1-, 3-, 5-, or 7veined, usually larger than others, lateral lobes 1-22 mm long, 1-or 3-veined, anterior lobes sometimes fused to a greater extent than other lobes, 2-31 mm long, yellow,pinkish,red,bluish, or purple, sometimes with colored markings within limb, 3.8-47 mm long, externally glabrous or pubescent, tube subcylindric to funnelform, throat inconspicuous or conspicuous and 6 equal to or longer than cylindric narrow proximal portion of tube, limb subactinomorphic to 2-labiate, upper lip 2-lobed, sometimes shorter than lower lip, lower lip lacking a bullate palate. Stamens 4 (rarely 2), usually didynamous, inserted in corolla tube, anthers included in tube or if slightly exserted from mouth of corolla then usually not (or but barely) extending beyond lips of corolla (rarely long-exserted, see discussion of S. macrobotrya below), thecae dehiscing toward lower lip (i.e., flower nototribic), broadly ellipsoid, 0.3-2.9 mm long, those of a pair parallel to widely divergent (i.e., thecae 6 end to end and horizontal [stamen T-shaped] to ''upsidedown'' [stamen Y-shaped]), equal to subequal in length, glabrous or pubescent, sometimes minutely mucronate near base (with mucro on side of theca opposite dehiscing side), connective sometimes expanded; staminode 0 or 1 (posterior) or rarely 2-3, inconspicuous; pollen oblate spheroidal to perprolate (P:E 5 0.95-2.31; polar axis 13-47 mm, equatorial axis 11-36 mm), 3-colpate to 3-colporoidate to 3-colporate, exine reticulate (sometimes appearing 6 foveolate in nonacetolyzed grains), muri smooth. Style included in corolla tube or if exserted from mouth of corolla then usually not extended beyond lips of corolla (except in S. macrobotrya), stigma not touch-sensitive, equally to unequally 2-lobed (sometimes appearing subcrateriform), 1 lobe again 2-parted (in some species), lobes linear (to broadly ovate-triangular), 0.2-2 mm long, 0.05-0.8 mm wide. Capsule subellipsoid to subcylindric to ovoid, 3-12 (-20) mm long, glabrous or pubescent (usually with glandular trichomes). Seeds up to 68 per capsule, spheric to ellipsoid to oblong to blocky or irregularly shaped, longest axis 0.3-1 mm, shortest axis 0.2-0.8 mm, surface coarsely lumpy-to foveolate-to rugulate-reticulate, microverrucate to microbaculate, pubescent with 6 hygroscopic trichomes, trichomes anchor-shaped to apically multibranched or sometimes trichomes branched throughout; (Fig. 21, 22). This, the richest genus of Nelsonioideae, contains 145 currently recognized species in tropical regions (Fig. 23) of the Americas (30 spp.), Africa (5 spp.), and mainland Asia to the Solomon Islands (110 spp.). The genus is especially well represented in southeastern Asia, Malesia, and Brazil. Due to a lack of recent studies of Acanthaceae from throughout Asia, the distributions of species occurring there, as noted in the catalog below, is not as complete as for species from other regions. The Malesian species were treated by Bremekamp (1955); African species, which are restricted to the Gulf of Guinea region, were treated by ; and the New World species were revised by . No species are common to both the New World and the Old World; and no species occurs in both Africa and the Asia-Malesian region.
Given the size of this genus, which is about four times as species rich as all other nelsonioid genera combined, and its broad distribution, the morphological diversity noted in the description above is not surprising. Diversity in habit, leaf shape, pubescence, inflorescence type, and floral characters has resulted in the recognition of numerous genera in a staurogynoid alliance. Only two of these are recognized here. Both Anisosepalum and Saintpauliopsis have been, and could with some justification yet be, included in Staurogyne; together, the former genera are sister to the geographically wide-ranging sample of 25 species of Staurogyne studied by McDade et al. (2012). Each of those genera also shares some morphological characteristics with Staurogyne, but each also  VOLUME 32, NUMBER 1 differs in several diagnostic features noted in the key above. Because of these diagnostic and unusual features, we prefer to recognize both Anisosepalum and Saintpauliopsis. Older names that are now treated as synonymous with Staurogyne were discussed by Bremekamp (1955) and Hossain (2004). Ancistrostylis T. Yamaz., a unispecific genus originally described in Scrophulariaceae based on a collection from Laos (Yamazaki 1980), was treated as congeneric with Staurogyne by Scotland and Vollesen (2000). Morphological characters enumerated in the protologue agree well with those of Staurogyne. The sole species has not been transferred to Staurogyne; whether it corresponds to a previously described species of that genus from southeastern Asia remains to be determined. Bremekamp (1955) noted that Gynocraterium was very similar to Staurogyne, from which it differed by its crateriform stigma and fewer number of ovules. Braz and Monteiro (2011) also noted the distinctive, elongate, and subulate bracts, bracteoles, and calyx lobes of the sole species, G. guianense. Subulate bracts and bracteoles are known elsewhere among Staurogyne (e.g., S. setigera). Braz and Monteiro (2011) noted between six and ten ovules per locule in their description of G. guianense, a range that does not distinguish the genus from other genera of Nelsonioideae in South America. Form of the stigma would appear to be the primary morphological character for distinguishing Gynocraterium from Staurogyne. Stigmas of Jansen-Jacobs 2852 (at U) that were hydrated and studied have two unequal (0.4 and 0.7 mm long) and broadly (1-1.2 mm wide) ovate-triangular lobes that result in a subcrateriform or funnel-shaped aspect. Although form of the stigma is not well documented among species of Staurogyne, and is often not well preserved on herbarium specimens, bilobed stigmas occur in the genus. Indeed, Hossain's (2004: Fig. 1L17) illustration of the stigma of S. subcordata showing two broad and flattened lobes are similar to those of G. guianense. Subcrateriform stigmas sometimes also occur in at least one species of Elytraria (i.e., E. caroliniensis; Fig. 15K). Intermediates or variations between funnel-shaped stigmas and bilobed stigmas in another genus of Acanthaceae (Thunbergia Retz.) are illustrated by Retief and Reyneke (1984: Fig. 3) and Schö nenberger (1999: Fig. 118). Given other similarities between G. guianense and species of Staurogyne and the molecular phylogenetic results of McDade et al. (2012), this putative morphological distinction would not seem sufficient to be the basis of a separate genus. Further, because current phylogenetic results (McDade et al. 2012) indicate that Gynocraterium is sister to all species of Staurogyne in the New World, if the former genus were to be recognized as distinct from the latter, then either all Neotropical species of Staurogyne would have to be transferred to Gynocraterium or a new genus would have to be recognized for them. Because morphological synapomorphies remain unknown for species of Staurogyne in the New World, neither of these alternatives seems prudent at present. Bremekamp (1955) also noted a close alliance between Ophiorrhiziphyllon and Staurogyne. He contended that the sole distinction for Ophiorrhiziphyllon was the exsertion of the stamens, and he noted ''this can hardly be regarded as sufficient to justify the maintenance of the genus'' (Bremekamp 1955: 160). Hossain (2004) further noted that several species of Staurogyne have shortly exserted stamens. Another unusual character of O. macrobotryum, the type of Ophiorrhiziphyllon, is the relationship between the anther connective and the two thecae. Among Nelsonioideae, the thecae are attached to the connective distally and are sometimes free from it (to a lesser or greater extent) proximally. Among species of Staurogyne both narrow and broad connectives are encountered, and the pair of thecae varies from parallel to sagittate to horizontal (i.e., each perpendicular to the connective and oriented apex to apex, thus stamen T-shaped). In O. macrobotryum the thecae are attached only at one end (presumably the distal end), and are divergent and erect (stamen Y-shaped) so that they appear ''upside-down.'' Somewhat similar thecae among species of Staurogyne were observed by us in S. setosa (Toroes 2320 at MICH), illustrated by Hossain (2004: 22, Fig . 1A) in S. subcordata, and illustrated by Champluvier (1991: 107, Fig. 3G) in S. capitata. Although the shapes and sizes of connectives and thecae differ among these four species, in all of them the thecae appear to be attached only at the apex and oriented ''upside-down.'' Because anthers are rarely described for species of Staurogyne, this unusual arrangement of thecae might be more common than is known. Considering phylogenetic relationships (McDade et al. 2012) and the apparent lack of significant morphological distinctions, there appears to be insufficient basis for recognition of Ophiorrhiziphyllon as distinct from Staurogyne. Bremekamp (1955) created an infrageneric classification for the Asian species of the Malesian region. He indicated that the classification of African and American species would have to await further studies, but suggested that they were not affiliated with the subgenera he recognized for Asian species. He recognized two subgenera, Staurogyne and Tetrastichum Bremek., based on the number of ovules, number of rows of ovules in each ovary cell, and inflorescence characters. Subgenus Staurogyne was divided into sections, subsections, and series based on differences in habit, inflorescence, bract, and calyces. Hossain (1971 dealt with the species on a worldwide basis, and proposed (but only partially published) a more extensive infrageneric treatment.  published sect. Zenkerina (Engl.) E. Hossain in subgen. Tetrastichum, and he proposed three unnamed series in subgen. Staurogyne, sect. Staurogyne, subsect. Staurogyne (as ''Macrosepalae Bremek.'') to account for species not treated by Bremekamp (1955) and/or that could not be accommodated in his classification for Malesian taxa.  provided descriptions of, and a key to, the five African species of Staurogyne. These all occur in tropical western Africa, primarily around the Gulf of Guinea in wet evergreen forests.  also discussed the disposition of the African species relative to Hossain's classification. She treated S. letestuana in subgenus Staurogyne and noted problems and inconsistencies in characters of other African species vis-à -vis their treatment by Hossain in sect. Zenkerina. She questioned the recognition of sect. Zenkerina based on its circumscription, but noted that the African species assigned to this section differ from S. letestuana by having: 1) capsules with a membranous wall, and that are tardily and apparently not explosively dehiscent, and 2) calyx lobes that converge and rest upon the capsule (even after dehiscence). At least the membranous wall of capsules in these species is apparently unique in the genus. Thus, additional studies are necessary to determine an appropriate taxonomic placement for most of the African species.  provided descriptions of, and a key to, 28 species of Staurogyne in the Neotropics. Profice (2000) described an additional Neotropical species, Staurogyne carvalhoi Profice, which according to  likely represents an undescribed genus of Acanthaceae with hypocrateriform corollas and three seeds per locule. This species was excluded from Braz's study, and we have not seen specimens of it.  noted two centers of richness for New World Staurogyne: southeastern Brazil (especially in the mata Atlâ ntica biome where 19 of the Neotropical species are restricted) and northern South America (especially in the Amazon forest biome of northern Brazil, the Guianas, and Venezuela).  concluded that based on  infrageneric taxa, all New World species of Staurogyne pertain to subsect. Staurogyne (as ''Macrosepalae''). Hossain's (1971) mostly unpublished infrageneric account of Staurogyne is particularly informative because he assigned most species to infrageneric taxa, which permits testing of his taxonomic hypotheses using molecular sequence data. Also,  used morphological data of mostly Neotropical species to construct a phylogeny for the species she studied. She concluded that Staurogyne was monophyletic, but that the Neotropical species were not (i.e., two Asian species were nested among those from the New World). Infrageneric relationships based on molecular phylogenetic data of McDade et al. (2012) confirm that Staurogyne is monophyletic (inclusive of Ophiorrhiziphyllon and Gynocraterium), and reveal the Neotropical species to be monophyletic and sister to those from the Old World. Although additional phylogenetic work is required to fully understand the relationships of species in the Old World, there is some support for those sampled from Asia as also being monophyletic (McDade et al. 2012).

Currently Recognized Species of Staurogyne
For this list the following sources provided most of the information about species currently recognized and their synonymies: Benoist (1935; southeastern mainland Asia), Bremekamp (1955;Malesia), Hossain (1971; worldwide), Africa), Hô (1993;Vietnam), Braz (2005; New World), and Hu et al. (2011;China). Numerous additional local floras in Asia, Malesia, Papuasia, and Australia were also consulted. Where there were conflicts, the most recent taxonomic interpretations were generally given preference. The list undoubtedly lacks some synonyms. Although all African  and New World  species have been revised recently, the majority of species occur in southern Asia and Malesia, and there is no recent comprehensive account of the genus in either of those regions.
Synonyms fide    noted that this species likely represented an undescribed genus of Acanthaceae, near or pertaining to Nelsonioideae. She noted several putative distinctions with respect to Staurogyne (e.g., corollas hypocrateriform and seeds three per locule). We have not seen specimens of it. Benoist (China, Vietnam) 27. Staurogyne ciliata Elm. (Philippines) Hossain (1971) indicated that this taxon should be treated as a variety of S. debilis, but did not publish a combination for it.