Microxyphiomyces

''Microxyphiomyces'' is a genus of lichen-forming fungi in the family Gomphillaceae. The genus was originally proposed in 1961 by Augusto Chaves Batista and colleagues, but was later merged into the genus ''Tricharia'' for much of the twentieth century before being reinstated in 2023 based on molecular evidence. These are minute lichens that grow exclusively on the surfaces of living leaves in tropical and subtropical forests, forming thin crusts decorated with fine black bristles and producing small disc-shaped reproductive structures. The genus has a pantropical distribution, with species recorded from the Neotropics, western Pacific, and East Asia.

Taxonomy

''Microxyphiomyces'' was circumscribed by Augusto Chaves Batista, R.C. Valle, and Generosa Emília Pontual Peres in 1961 for a foliicolous (leaf-dwelling) lichen that had previously been shuffled among several imperfect fungus genera. Their protologue designated ''M. manaosensis'' as the type species; that name is now treated as a synonym of ''M. vainioi'', which therefore serves as the modern type species. A second, invalid generic name (''Setomyces'' ) was published almost simultaneously for the same material and is treated as a heterotypic synonym.

For much of the twentieth century the genus was folded into the widespread and morphologically variable ''Tricharia'' because its smooth thallus and delicate, sterile were considered minor variants within that assemblage. Phenotypic cladistic work first hinted that the "''T. vainioi'' group" formed an independent lineage, and two-locus molecular phylogenies later confirmed that it is only distantly related to the core species of ''Tricharia''. On that evidence, Xavier-Leite and colleages reinstated ''Microxyphiomyces'' in 2023, transferred fourteen names into it, and restricted ''Tricharia'' to species with coarsely thalli and stout setae.

Description

''Microxyphiomyces'' species are minute, leaf-dwelling lichens that form a thin, continuous thallus closely to the leaf surface. The thallus is smooth rather than warted and ranges from pale greenish to grey-green; it is thread through with fine, black, sterile bristles (setae) that emerge singly or in loose tufts and give the colony a subtle, bristly sheen. These setae are markedly slimmer and more flexible than those seen in ''Tricharia'' (in the strict sense), a difference that, together with the unbroken thallus surface, makes the genus recognisable in the field.

The fruit-bodies (apothecia) sit directly on the thallus. Most species develop small, discs—meaning the margin derives solely from fungal tissue—whose pale to orange-brown centres contrast with a thin, paler rim; in a few taxa the discs break through the thallus and become shallowly bowl-shaped (a form). Setae often arise around or between apothecia but never grow from the itself. Internally, the hymenium produces eight colourless ascospores per ascus. Spores start with only a few cross-walls (septa) and mature through additional septation into short, brick-like chambers ( pattern); they are released as single-celled propagules that rely on wind or water splash for dispersal.

A second reproductive device, the , is common in the genus. These structures look like hair-thin black pins that may remain simple, curve in a gentle hook, or branch sparsely toward the tip. Each hyphophore bears chains of tiny, bead-like cells () that break apart to function as vegetative diaspores. The three informal morphodemes recognised by Xavier-Leite and colleagues correspond to differing combinations of apothecial form and hyphophore architecture: ''Microxyphiomyces'' sensu stricto with simple hyphophores and biatorine apothecia; the ''M. lancicarpus'' complex with chroodiscoid apothecia; and the ''M. elegans'' group characterised by uniquely hooked or branched hyphophores.

Habitat and distribution

All known members of ''Microxyphiomyces'' are obligately foliicolous: they colonise the surfaces of living, evergreen leaves in the shaded understory of humid tropical to subtropical forests. The smooth, tightly appressed thallus adheres directly to the cuticle, while the flexible black setae and pin-like hyphophores project into the thin, persistent boundary layer of moisture that forms on leaf blades. These features appear to be adaptations to the periodically wet yet well-aerated microclimate typical of intact rainforest canopies and leaf litter, and the genus has not been recorded on bark, wood or rock.

The genus has a broad pantropical distribution. Sequenced or type specimens come from the Neotropics (Costa Rica, Brazil, French Guiana and Paraguay), the western Pacific (Papua New Guinea) and the Palaeotropics of East Asia (Japan). Although no confirmed African collections have yet been reported, the occurrence pattern of related foliicolous Gomphillaceae suggests that suitable habitat is available and the genus is probably under-collected there. At present, the greatest species richness is documented from South America, where multiple morphodemes occur sympatrically on the same forest strata.

Species

* '' Microxyphiomyces cuneatus''
* '' Microxyphiomyces demoulinii''
* '' Microxyphiomyces elegans''
* '' Microxyphiomyces kashiwadanii''
* '' Microxyphiomyces lancicarpus''
* '' Microxyphiomyces santessonianus''
* '' Microxyphiomyces santessonii''
* '' Microxyphiomyces similis''
* '' Microxyphiomyces vainioi''
* '' Microxyphiomyces variratae''

References

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Gomphillaceae
Lichen genera
Graphidales genera
Taxa described in 1961
Taxa named by Augusto Chaves Batista