Description
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 ( areoles ) 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 ( blastidia , goniocysts ) 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 pruina , and some have a dead, transparent epinecral film that gives a slightly glazed look. The upper cortex 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 chlorococcoid type, which nestles within the medulla just beneath the cortex. [5]
The sexual fruiting bodies are tiny, stalk-less discs (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. [5]
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). [5]
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