Physconia Labrata

''Physconia'' is a genus of lichen-forming fungi in the family Physciaceae. It comprises 13 species. The genus was established in 1965 by the lichenologist Josef Poelt and is characterized by leaf-like growth forms with typically less than 3 mm wide that often have a whitish, powdery coating on their tips. These lichens can be distinguished from similar genera by their distinctive brown ascospores that have thick walls, fine warts, and a single dividing wall but lack the end thickenings found in related groups.

Taxonomy

The genus was circumscribed by the Czech lichenologist Josef Poelt in 1965, with '' Physconia pulverulenta'' assigned as the type species.

Description

''Physconia'' lichens form leaf-like (foliose) rosettes whose are usually less than 3 mm wide. Colonies can be neat and roughly circular or irregular mats merging with neighbouring thalli. The lobes lie fairly close to the surface but are not tightly glued down and lack the fringe hairs (cilia) seen in some related genera. Upper surfaces range from dull grey to dark brown and are matt or only faintly glossy; a thin, whitish frost (pruina) commonly dusts the lobe tips. Some species also produce soredia—powdery granules that break off and serve as ready-made propagules. The underside is whitish to brown-black and may lose its lower near the lobe tips. Internally, the upper cortex is built either from block-like cells about 3–7 Î¼m across or from densely packed hyphae with much smaller ; the lower cortex is always of the latter type. The photosynthetic partner is a green alga of the ''Trebouxia'' group.

Fruiting bodies (apothecia) sit on the lobe surfaces and lack the root-like rhizines sometimes found beneath other genera. Their are brown but almost always coated in white pruina. A collar of thallus tissue (the ) surrounds each disc; it persists, often curls slightly inward and may bear tiny or soredia. Microscopy shows a brown topping a colourless hymenium and . Ascospores develop eight to an ascus and match the "''Physconia'' type": they are thick-walled, single-septate, finely warted and brown, with a broad internal cross-wall but no extra thickening at the ends—one of the main features separating the genus from ''Physcia''. Asexual propagules form in immersed pycnidia whose walls are mostly colourless except around the pore; these structures release rod-shaped, colourless conidia. Chemical tests detect no atranorin and, at most, trace amounts of unidentified lichen substances.

Species

, Species Fungorum (in the Catalogue of Life) accept 13 species of ''Physconia''.
*'' Physconia californica''
*'' Physconia chinensis''
*'' Physconia distorta''
*'' Physconia enteroxantha''
*'' Physconia fallax''
*'' Physconia grisea''
*'' Physconia jacutica''
*'' Physconia labrata''
*'' Physconia muscigena''
*'' Physconia perisidiosa''
*'' Physconia pulverulenta''
*'' Physconia rossica''
*'' Physconia sikkimensis''
*'' Physconia thorstenii''

References

{{Taxonbar, from=Q7189532

Caliciales
Lichen genera
Caliciales genera
Taxa described in 1965
Taxa named by Josef Poelt