Costus loangensis, an exciting new species from Gabon, Africa

Abstract A new species of spiral ginger (Costus: Costaceae) from Gabon, Africa is described. Costus loangensis H. Maas & Maas is found in the coastal region on white sand soils under a tropical rain forest canopy. It is morphologically distinct from all other African species of Costus but shows some similarities in floral form with the savanna-inhabiting Costus spectabilis (Fenzl) K. Schum. and similarities in vegetative form with Costus ligularis Baker. Only one population of the new species is documented. Photographs of the new species are included as is a preliminary phylogeny indicating its position within the African Costaceae.


Introduction
Th e plant family Costaceae is pantropical in distribution with its largest genus, Costus L., restricted in distribution to African and New World Tropics. Based on phylogenetic studies, the ancestral distribution of Costus is the African tropics and its current distribution is refl ective of a long distance dispersal event from Africa to the neotropics (Specht et al. 2001). Estimates based on fossil calibrations indicate that the Neotropical lineage diverged from the African Costus clade approximately 33 million years ago (Specht 2006b), while subsequent diversifi cation of the neotropical Costus lineage based on rates of molecular evolution is estimated to have occurred within the past 4 million years (Kay et al. 2005), indicating a recent rapid radiation of the neotropical Costus lineage following colonization. Th ere are currently ~80 species in the new world clade as compared with only ~25 species in the combined African lineages.
In all Costus species, the staminodial labellum, formed by the fusion of fi ve petaloid organs in the stamen whorl, is predominantly responsible for the fl oral display. Th e ancestral Costus fl ower had a broad, open labellum; solid white or yellow in color; with no strong markings indicative of a specifi c pollination syndrome (Specht et al. 2001). Phylogenetic studies using molecular and morphological data (Specht 2006a) indicate a single evolutionary origin of the bee-pollinated fl oral form from the ancestral open fl oral morphology, resulting in a relatively diverse African clade (~7 species) all with a fl oral morphology indicative of bee pollination (e.g. Costus afer Ker Gawl., Costus dubius (Afzel.) K. Schum). Th e Neotropical Costus lineage is sister to this beepollinated African clade, and the earliest diverging species of the neotropical clade retain the ancestral bee-pollination syndrome (Specht 2006b;Kay et al. 2005). Within the neotropical Costus, bird pollination has evolved as many as 7 times, each associated with a radiation of a bird-pollinated lineage (Kay et al. 2005, Specht 2006a). It is hypothesized that this evolutionary toggle between bee and bird pollination and adaptation to hummingbird pollination (Kay et al. 2005) may have led to the rapid radiation of this lineage in the Neotropics subsequent to its divergence from the African ancestral populations (Specht 2006b). Th ere are no known bird-pollinated species in Africa, with the possible exception of Costus giganteus Welw. ex Ridl. from São Tomé and Principe which bears red bracts and tubular yellow fl owers that resemble those of Neotropical bird-pollinated species.
As part of a larger eff ort to monograph all African species of Costus, the authors recovered a photograph of a Costus fl ower published in a guide to the Loango National Park (Vande weghe 2007). Th is photo represented a plant that was not present in studied herbarium or living material and had not yet been described. An expedition to Gabon with a targeted trip to the Loango National Park (= Parc Nacional de Loango) and the surrounding region revealed a single population of the unknown species, here described.  a dense indument of erect to half-appressed hairs. Costus loangensis diff ers from Costus spectabilis (Fenzl) K.Schum., another short-stemmed yellow-fl owered species, by having a well developed aerial stem. Costus spectabilis inhabits savannas and has only 4 leaves that remain strongly pressed to the ground. Costus loangensis diff ers from Costus ligularis Baker, also a short-stemmed and indumented plant, by the colour of its fl owers (Costus ligularis has a pale pink fl ower) and the length of the calyx (5-7mm in C. ligularis v. 11-12mm in C. loangensis) ( Description. Terrestrial herb, 0.5-0.6 m tall, stems dark brownish red. Leaves: dark olive-green, several (6-7) concentrated at the apex of the stem; sheaths dark red, 0.6-0.8 cm diam.; ligule green, 2-lobed, 15-18 mm long, membranous; petiole 5-6 mm long; sheaths sparsely to rather densely covered with erect to half-appressed hairs ca. 2 mm long, ligule and petiole densely to rather densely so; lamina narrowly elliptic to elliptic, 14-16 by 5-6 cm, densely to rather densely covered with erect to half-appressed hairs 1.5-2 mm long on both sides, zone along midrib sometimes reddish, base attenuate, apex acute. Infl orescence: 3-5-fl owered, ovoid, 2 by 1-1.5 cm, terminating the leafy stem; outer side of bracts, bracteoles and calyx densely covered with appressed to half-appressed hairs ca. 0.2 mm long, ovary sparsely so. Flower: 1 per bract; bracts brown to reddish brown, chartaceous, narrowly ovate-triangular to ovate-triangular, 1.7-2 by 0.5-1 cm, callus 2.5-3 mm long; appendages absent; bracteole reddish, boat-shaped, 15-18 mm long, callus 1.5-2 mm long; calyx reddish to greenish, 11-12 mm long, lobes deltate, ca. 2 mm long, callus ca. 1 mm long; corolla yellow, 50-55 mm long, tube 20-25 mm long, lobes narrowly elliptic, 30-35 mm long, outer side rather densely covered with half-appressed hairs ca. 1 mm long particularly near the apex, together forming a hood over the throat opposite the labellum, apex with a callus-like thickening; labellum yellow, horizontally fl attened with funnel-shaped base, broadly obovate when spread out, 30-40 by 40-50 mm, margin fi mbriate (fi mbriae 2-3 mm long); stamen yellow, 25-30 by 7-10 mm, apex refl exed, anther 5-7 mm long; ovary narrowly obovoid, ca. 6 mm long, stigma bilamellate, dorsal appendage 2-lobed. Fruit and seeds not seen.
Distribution. Gabon (Fig. 2). Only known from the type location. Habitat and ecology. In wet forest, on white sand soil under rain forest canopy (Fig. 3). Elevation just above sea level. Flowering: November; fruiting: unknown.   Phylogenetic relationship. Based on a combined 4 molecular marker (CAM, ITS, ETS, rpb2) phylogenetic analysis with taxon sampling that included African species in the genus Costus, Costus loangensis H. Maas & Maas is found to be well supported as sister to a clade of Costus ligularis Baker specimens (Fig. 4). Costus loangensis fi ts within the general distribution range of C. ligularis, however no populations of Costus ligularis were found in sympatry. Costus loangensis is restricted in elevation to just above sea level, while C. ligularis is commonly found 0-600m above sea level throughout lowelevation rain forests in Cameroon and Gabon. Vernacular names. Not recorded. Th is plant seems to go unnoticed by the local population and has no known uses.
Etymology. Costus loangensis is named after the place where it was photographed and now has been collected and documented for the fi rst time: near the Loango Lodge, in "Parc Nacional de Loango" in Gabon.  (Table 2) including newly described Costus loangensis. Th e phylogeny was constructed in PhyML (Guindon and Gascuel 2003) with aligned sequence data for two low copy nuclear markers [calmodulin (cam) intron (Johansen 2005) and rpb2 (Specht 2006a)] and nrDNA markers ITS and ETS. All nodes indicated have >50% bootstrap support.

Acknowledgements
Th e authors thank Mr. Jean Pierre Vande weghe for his invaluable help in locating the plants, for sending us photographs, and for the permission to use his photographs in this publication. We are highly indebted to the director of Africa's Eden, Mr. R. Swanborn, for making it possible for the authors to stay in "Parc Nacional de Loango" and to search there for this plant; to Dr. Frans Breteler for helping to organize the fi eld expedition, assistance in collection and identifi cation, and superb logistic and botanical support; to Raul Niangadouma (Herbarium LBV in Libreville, Gabon) for fi eld assistance, guidance and for sharing his extensive knowledge of Gabon's native fl ora; and to Dr. Bas Verhage, WWF Gamba Programme Manager in Gabon, for expert advice prior to the trip and logistic support during our fi eldwork in and around Loango and the Mandji area of Gabon. HMK and PJMM thank the "Hugo de Vries-fonds" and the "Society for the advancement of research in the tropics" (Treub-Maatschappij) for fi nancial support. CDS acknowledges the National Geographic Society Committee for Research and Exploration (grant #8994-11) for fi nancial support for travel to Gabon and S. Salzman, T. Renner, S. Shen, and K. Yu for producing and analyzing the phylogenetic data presented in this paper.