Description
Enterographa species grow as thin, paint-like crusts that either lie smoothly on the bark or break into a network of tiny, flat blocks ( areoles ). Colours range from off-white and pale grey to dark olive-green or brown, and neighbouring colonies often form mosaic patterns separated by a narrow, grey-to-black prothallus —the band of purely fungal tissue at the thallus edge. Because the crust is not layered, the algal partner ( Trentepohlia ) sits directly beneath the surface and lends a faint orange hue where the thallus is scratched. A few species are lichenicolous, living on other lichens; in these the parasite produces only its reproductive bodies and lacks a thallus of its own. Thin-layer chromatography shows a variable secondary chemistry: some taxa contain acids such as confluentic, gyrophoric, protocetraric or psoromic, while others appear chemically inert. [4]
The sexual fruit bodies are tiny slits or dots immersed in the crust. They range from pin-prick pores to short, narrow lirellae that can be straight, gently curved or, rarely, star-shaped. Their exposed discs are flat and brown-to-black, never dusted with the pale frosting ( pruina ) seen in certain related genera. The surrounding wall ( true exciple ) remains thin and stays buried in the thallus, so only the opening is usually visible from above. Inside, the spore layer (hymenium) is threaded by very slender filaments (paraphyses) that branch and fuse near the top but lack the swollen tips typical of many other crustose lichens. Each ascus is long and narrow, splitting open to release either four or eight spindle-shaped ascospores. A microscopy stain with iodine picks out a tiny, dark blue ring around the ocular chamber at the ascus apex, while the rest of the apex often turns pale blue. The spores are colourless, multi-celled (three to sixteen internal walls) and gently tapered at both ends. [4]
Asexual reproduction occurs in microscopic, flask-shaped pycnidia embedded in the crust; these appear as minute, pale-brown specks. Inside, cylindrical conidiogenous cells bud off colourless, rod-shaped conidia that escape through a small pore and help the fungus spread independently of its algal partner. Together, the combination of an immersed thallus lacking a cortex, slit-like apothecia with an inconspicuous wall, very thin paraphyses, iodine-reactive asci and multi-septate spores distinguishes Enterographa from superficially similar crusts on tropical and temperate bark. [4]
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