Involucropyrenium species have a minute but robust body (
thallus) that consists of tiny, overlapping —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 () is a unicellular
green alga of the type. An upper only 10–30
micrometres (μm) thick overlies the ; 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 . Reproduction takes place in
perithecia—flask-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
ostiole—the pore through which spores exit—while 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==