Lithothelium is a genus of
crustose lichens, meaning its
thallus—the main body of the lichen—forms a thin, crust-like layer that can either remain embedded within the
substrate or lie on its surface. Some species have a
green algal partner from the genus
Trentepohlia, while others may lack a altogether. The reproductive structures, called
perithecia, are flask-shaped fruiting bodies that are typically black and can occur either individually or in fused clusters. These have an
ostiole—a small opening through which spores are released—that is usually located at the top but may also be offset to the side. Inside the perithecia, the fertile tissue (the ) consists of slender, unbranched or slightly branched filaments called
paraphyses. These lack , which are short hairs found in some other lichenised fungi. The gel that surrounds the
hymenium (spore-producing layer) may show weak blue or orange staining in iodine-based
staining, although the
ascus wall itself does not react (K/I–). The asci usually contain 6 to 8
spores and typically have a rounded or three-lobed () , a small structure near the apex that assists in spore discharge. The
ascospores may be colourless or brown, with three to seven cross-walls (
septa) or occasionally with a more complex somewhat (brick-like) structure. All septa are —meaning the cross-walls are thickened and distinct—and the individual spore compartments (cell ) tend to be rounded in shape.
Asexual reproduction occurs through
pycnidia, small specialised structures that produce long, threadlike (), non-septate
conidia. No
secondary metabolites (
lichen products) have been detected in this genus using
thin-layer chromatography. ==Ecology==