Thalloloma

''Thalloloma'' is a genus of lichen-forming fungi in the family Graphidaceae. Established in 1853 by the Italian botanist Vittore Trevisan de Saint-Léon, the genus comprises 20 species distinguished by their narrow script-like slits immersed in a pale crusty surface, often with dark brown or occasionally crimson-dusted fruiting structures. Found throughout tropical regions from sea level to mountain forests above 3,000 metres, these bark-dwelling lichens are more tolerant of light and moisture variation than many related species, allowing them to colonise forest edges and moderately sun-exposed locations.

Taxonomy

The genus was circumscribed in 1853 by the Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon. In his original description, Trevisan characterised ''Thalloloma'' by its immersed apothecia (fruiting bodies) that are either deformed, oblong, or -like in extension, with longitudinal slits that are surrounded by a prominent and lack a . He noted the brownish , eight-spored asci with enclosed paraphyses, and cylindrical, , muriform ascospores. Trevisan described the thallus as crustaceous and uniform. In his subtribe classification of the Sclerolites, Trevisan distinguished ''Thalloloma'' from related genera: ''Ustalia'' (with pyrenoid apothecia), '' Sclerophyton'' (with lenticular apothecia), and ''Fissurina'' (with simple spores), noting that his new genus differed from ''Ustalia'' by having muriform rather than longitudinally plurilocular spores. He included several species within the genus, establishing '' Thalloloma anguinum'' (previously ''Ustalia anguina'') as the type species.

Description

''Thalloloma'' forms a thin, pale grey-white to grey-green crust (thallus) that lacks a true and is peppered with minute crystals. Its —narrow, script-like slits—are immersed in the thallus so only their fine, entire lips show; the surrounding is usually conspicuous and may break into irregular lobes. Each slit exposes a dusted with dark brown or occasionally crimson , the latter tint produced by the pigment isohypocrellin. Unlike many script lichens, the encircling tissue () never becomes .

Inside, the hymenium is clear (non-) but partly , and the smooth paraphyses stand beside ''Graphis''-type asci. Each ascus typically releases eight hyaline, ascospores with lens-shaped compartments that stain violet in iodine (I+). Secondary chemistry is modest: most species contain (thallus UV+ yellow), while those with crimson discs additionally produce the anthraquinone isohypocrellin.

Species of ''Thalloloma'' can be mistaken for ''Diorygma''—both have an thallus and powdery discs—but ''Thalloloma'' lacks the white pruina, diverse depsidones and branched paraphyses that typify ''Diorygma''. It also differs from brown-spored '' Phaeographis'' in its inspersion-free hymenium and hyaline, I+ spores.

Ecology

The genus is pantropical in distribution, ranging from sea-level mangroves to montane forests above 3000 m in elevation. It colonises moderately exposed bark in both ever-wet and seasonally dry woodlands; its tolerance of light and moisture variation allows it to occur in gap edges and upper understory rather than the deepest shade.

Species

, Species Fungorum (in the Catalogue of Life) accept 20 species in ''Thalloloma'':
*'' Thalloloma anguinum''
*'' Thalloloma astroideum''
*'' Thalloloma buriticum''
*'' Thalloloma castanocarpum''
*'' Thalloloma cinnabarinum''
*'' Thalloloma deplanatum''
*'' Thalloloma haemographum''
*'' Thalloloma halonatum''
*'' Thalloloma intermedium''
*'' Thalloloma isidiosum''
*'' Thalloloma janeirense''
*'' Thalloloma microsporum''
*'' Thalloloma nitidum''
*'' Thalloloma ochroleucum'' – China
*'' Thalloloma patulum''
*'' Thalloloma pedespulli''
*'' Thalloloma pontalense''
*'' Thalloloma rhodastrum''
*'' Thalloloma rubromarginatum''
*'' Thalloloma scribillans''
*'' Thalloloma subvelata''
*'' Thalloloma xanthohypoleptum''

References

{{Taxonbar, from=Q7709718

Graphidaceae
Graphidales genera
Lichen genera
Taxa named by Vittore Benedetto Antonio Trevisan de Saint-Léon
Taxa described in 1853