Rostania
Rostania is a genus of lichen-forming fungi in the family Collemataceae. These lichens are primarily found on tree bark, occasionally on wood, with one species known to inhabit soil. The genus is characterized morphologically by having minute thalli made of hyphal tissue without a separate , and the more or less cuboid-shaped . Taxonomy
The genus was originally circumscribed in 1880 by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon. In its new, restricted sense, following its revision using molecular phylogenetics and subsequent resurrection, Rostania is equivalent to the Collema occultatum group as defined by Gunnar Degelius in 1954. The taxonomy of the non-monophyletic taxon Rostania occultata is recently been clarified, and revised generic limitations of the genus proposed, such that some species have been excluded and transferred to other genera. Description
Rostania features lichens with a somewhat crustose to  thallus that is relatively small, measuring  in diameter. These lichens exhibit dark olive green, black, or brownish colours and can either form a diffuse granular crust or have poorly developed  up to 1 or 2 mm wide. The lobes are smooth to ridged and lack a true . The medulla consists of hyphal structures intermingled with chains of Nostoc photobiont cells; a  is absent in Rostania species. Isidia are not present in this genus; however, accessory teretiform  (i.e., small, cylindrical extensions) may develop from . The apothecia are , sessile, and , resembling  in their early stages. The  colour ranges from very pale brownish to dark red-brown. The  is distinct and smooth, either entire or , and may become excluded over time. The  is colourless to reddish-brown and does not react with a solution of potassium hydroxide or ammonia. The hymenium is colourless and turns blue when exposed to iodine. The  is shallow, either colourless or pale yellowish. The  comprises numerous,  paraphyses that are mostly unbranched, with somewhat swollen apices. The asci are clavate and contain two, four, or eight spores, with the wall and  turning blue in response to potassium hydroxide and iodine. The ascospores are broadly cylindrical to more or less spherical, often cuboid, and . may be present in some species, embedded within the thallus. The conidia are  and hyaline. No lichen products have been detected in Rostania species using thin-layer chromatography. Species
, Species Fungorum (in the Catalogue of Life) accepts 9 species of Rostania. Rostania callibotrys 
 Rostania ceranisca 
 Rostania coccophylla 
 Rostania effusa 
 Rostania laevispora 
 Rostania multipunctata 
 Rostania pallida 
 Rostania occultata 
 Rostania populina 

Because Rostania callibotrys does not group with Rostania in molecular phylogenetic analysis (instead forming an unsupported group with Enchylium), Košuthová and colleagues suggest that its placement in this genus is uncertain. Rostania laevispora is rarely collected and has not yet had its DNA analysed, but its morphology suggests a close relationship with R. callibotrys. Another seldom-collected species, R. coccophylla, may be better placed in the genus Collema. The taxon once known as Rostania quadrifida  is now Scytinium quadrifidum. Rostania paramensis  was transferred to Leptogium, as Leptogium paramense. References

Peltigerales
Lecanoromycetes genera
Lichen genera
Taxa described in 1880
Taxa named by Vittore Benedetto Antonio Trevisan de Saint-Léon