Description
Schismatomma species form a thin, crust-like thallus that lies more or less flush with the bark or rock surface. Where colonies meet they may be separated by a dark brown to black fringe (the prothallus ), and some species develop powdery reproductive patches called soralia that can mask the underlying crust. A quick scratch of fresh material exposes an orange stain—pigment from the filamentous alga Trentepohlia , which supplies the photosynthetic partner in every species. Because the crust lacks a true outer skin ( cortex ) the algal layer sits immediately beneath the fungal tissue. [2]
Sexual fruit bodies (apothecia) start embedded in the thallus but often emerge to become small, slightly irregular discs . Each is ringed by a rim of thallus tissue ( thalline margin ), while the fruit body's own wall ( true exciple ) remains poorly developed and soon blends into the surrounding crust. Internally, the spore-bearing layer (hymenium) stains blue in iodine and is threaded by branched, interwoven filaments ( paraphysoids ). Beneath lies a dark olive to black hypothecium that may be scarcely visible in thin specimens. The asci are club-shaped and split open ( fissitunicate ) to release eight spindle-shaped to gently curved ascospores, each divided by several cross-walls; the spores are colourless when young, may brown slightly with age, and can coil inside the ascus before discharge. [2]
Asexual propagation occurs in flask-shaped pycnidia sunk within the thallus. Their lining cells bud off minute, rod-shaped conidia—straight, curved, or kidney-shaped—that escape through a tiny pore and disperse independently of the alga. Chemical analysis shows wide variation: different species may contain orcinol-type depsides such as lecanoric acid or erythrin, β-orcinol compounds like fumarprotocetraric or psoromic acids, yellow chromones, fatty acids, or remain chemically undetected. Morphologically the genus resembles Enterographa and Lecanactis , but it is set apart by the presence of a thalline margin around the apothecia and a much reduced exciple. [2]
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