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

{{Taxonbar, from=Q23072882

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