Involucropyrenium

Involucropyrenium species have a minute but robust body (thallus) that consists of tiny, overlapping squamules—scale-like lobes—which 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 (photobiont) is a unicellular green alga of the chlorococcoid type. An upper cortex only 10–30 micrometres (μm) thick overlies the algal layer; it is uneven, poorly separated from the tissue beneath, and built from small, polygonal cells 5–8 μm across. A distinct lower cortex is absent, so the hyphae merge directly into the substratum.^[2]

Reproduction takes place in perithecia—flask-shaped fruiting bodies that push up between the squamules. Each perithecium is capped by an involucrellum, a dark sheath that may cover just the apex, half-wrap the wall, or surround it entirely. The perithecial wall (exciple) comprises elongated cells arranged parallel to the surface; it is often darkened around the ostiole—the pore through which spores exit—while the lower portion ranges from pale to blackish. Only short ostiolar threads (periphyses) 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.^[2]

No specialised asexual structures (conidiomata) have been observed, and thin-layer chromatography has yet to detect any secondary metabolites.^[2]

As of June 2025^[update], Species Fungorum (in the Catalogue of Life) accepts 10 species of Involucropyrenium:^[3]

• Involucropyrenium altimontanum Breuss & Türk (2021)^[4]
• Involucropyrenium breussii A.B.Gromakova & S.Y.Kondr. (2017)^[5]
• Involucropyrenium llimonae (Etayo, Nav.-Ros. & Breuss) Breuss (2004)
• Involucropyrenium nuriense (Nav.-Ros. & Breuss) Breuss (2004)
• Involucropyrenium pusillum Breuss & Türk (2004)^[6]
• Involucropyrenium romeanum (B.de Lesd.) Breuss (2016)
• Involucropyrenium sbarbaronis (Servít) Breuss (1996)
• Involucropyrenium terrigenum (Zschacke) Breuss (1996)
• Involucropyrenium tremniacense (A.Massal.) Breuss (1996)
• Involucropyrenium waltheri (Kremp.) Breuss (1996)