Platythecium
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| Platythecium | |
|---|---|
_Figure_6B.jpg) | |
| Platythecium pyrrhochroum; scale bar = 1 mm | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Lecanoromycetes |
| Order: | Graphidales |
| Family: | Graphidaceae |
| Genus: | Platythecium Staiger (2002) |
| Type species | |
| Platythecium grammitis (Fée) Staiger (2002) | |
Platythecium is a genus of lichen-forming fungi in the family Graphidaceae. It comprises 25 species.[1] Described in 2002 by the German lichenologist Bettina Staiger, these bark-dwelling lichens are found in humid, shaded forests across tropical and warm temperate regions worldwide. They are characterized by their flattened, plate-like fruiting structures with completely blackened walls and are sensitive to forest disturbance, making their presence an indicator of long-established woodland conditions.
The genus was circumscribed in 2002 by the German lichenologist Bettina Staiger in her 2002 monographic treatment of the family Graphidaceae. Platythecium grammitis was assigned as the type species.[2]
Description
Platythecium produces a smooth, pale grey-green to yellow-olive crust (thallus) that embeds directly in the bark and lacks a true cortex. Its fruit bodies are short to elongate lirellae whose slate-black walls are completely carbonised; the narrow slit is usually covered at first by a thin thalline veil that later breaks to reveal a flat, often faintly white-pruinose disc. Beneath the margin a colourless to pale brown excipulum lines a clear, non-inspersed hymenium traversed by smooth paraphyses. Eight hyaline ascospores develop in each Graphis-type ascus; they become conspicuously muriform—divided by many transverse and a few longitudinal septa—but remain iodine-negative (I–) and generally measure 25–60 × 8–15 μm. Most species are chemically inert or contain only low amounts of stictic acid-series depsidones, a contrast to many anthraquinone-rich script lichens. [3]
The flattened, plate-like lirellae and pale excipulum distinguish Platythecium from superficially similar genera. In Glyphis and Hemithecium the discs stay narrow and the walls alone form the exposed edge, whereas Platygramme displays broader shields with a persistent thalline rim, and Kalbographa is set apart by its vivid orange to brick-red epithecium produced by anthraquinones. [3]