Involucropyrenium is a genus of lichens in the family Verrucariaceae. It has 10 species. Species in this genus are characterised by their minute, scale-like growth form and distinctive reproductive structures capped with dark sheaths. Most of the ten recognised species were described relatively recently, with several new species added as recently as 2021.
The genus was circumscribed by the Austrian lichenologist Othmar Breuss in 1996, with Involucropyrenium waltheri assigned as the type species.
Involucropyrenium species have a minute but robust body (thallus) that consists of tiny, overlapping âÂÂscale-like lobesâÂÂwhich in some taxa coalesce into a thin crust. These squamules are anchored to rock or bark by a mesh of colourless to brown, root-like fungal threads (rhizoidal hyphae). The photosynthetic partner () is a unicellular green alga of the type. An upper only 10âÂÂ30 micrometres (üm) thick overlies the ; it is uneven, poorly separated from the tissue beneath, and built from small, polygonal cells 5âÂÂ8 üm across. A distinct lower cortex is absent, so the hyphae merge directly into the .
Reproduction takes place in peritheciaâÂÂflask-shaped fruiting bodies that push up between the squamules. Each perithecium is capped by an , a dark sheath that may cover just the apex, half-wrap the wall, or surround it entirely. The perithecial wall () comprises elongated cells arranged parallel to the surface; it is often darkened around the ostioleâÂÂthe pore through which spores exitâÂÂwhile the lower portion ranges from pale to blackish. Only short ostiolar threads () occupy the cavity; the interascal filaments seen in many lichens are lacking. The spore sacs (asci) are club-shaped, thin-walled, non-amyloid (they do not stain blue in iodine), and contain eight colourless, single-celled ascospores arranged in two rows. The spores are broadly ellipsoidal to ovoid.
No specialised asexual structures (conidiomata) have been observed, and thin-layer chromatography has yet to detect any secondary metabolites.
, Species Fungorum (in the Catalogue of Life) accepts 10 species of Involucropyrenium: