Lecania forms a crustose
thallus—that is, a thin, paint-like growth tightly attached to the
substrate. Depending on the species, this crust may be only a fraction of a millimetre thick or develop into a more robust layer that cracks into tiny plates () or wart-like bumps. In a few
taxa the surface becomes minutely lobed or covered with powdery reproductive tissues such as
soralia or tiny grain-like
propagules (, ) that help the lichen spread
vegetatively. Colours range from grey-white and pale yellow to deep brown-black; many specimens acquire a frost-like coating of minute crystals called , and some have a dead, transparent film that gives a slightly glazed look. The upper is built of tightly packed fungal cells, though in some species this layer is so saturated with crystals that its cellular structure is obscured. The
photosynthetic partner is always a single-celled
green alga of the type, which nestles within the
medulla just beneath the cortex. The
sexual fruiting bodies are tiny, stalk-less (
apothecia) that appear flat when young but often bulge into low domes with age. Measuring roughly 0.4–0.6 mm across (occasionally up to 1 mm), these discs vary in colour from pale brown through orange to almost black and may also carry a dusting of pruina. They are usually rimmed by a thin band of thallus tissue, though this margin can erode in older specimens. Viewed in section, the
hymenium (the fertile layer) is colourless but turns blue when
stained with
iodine. Slender
paraphyses thread through the
hymenium; their tips often swell or darken, giving a
mottled, "
piebald" appearance when the disc is wetted. Each
ascus ordinarily houses eight colourless
ascospores (occasionally up to sixteen) that are one- to three-
septate, though some species may have spores with as many as seven internal walls. Spores are thin-walled, sausage- to spindle-shaped, and longer examples can curve gently.
Asexual reproduction is common on bark-dwelling species: flask-shaped
pycnidia produce tiny, curved
conidia. Most
Lecania species lack distinctive
secondary metabolites, but a few contain the
lichen substance atranorin or various unidentified
terpenes. Pigments within the apothecia sometimes give positive colour reactions with standard chemical
spot tests (K or N). ==Species==