Description
Dermatocarpon lichens form grey-brown sheets that range from minute overlapping scales ( squamules ) to broad, leaf-like lobes ( foliose thalli). Each thallus is anchored by one or several stout holdfasts that act like suction pads; the lower surface otherwise lacks the root-like rhizines common in many rock-dwelling lichens, although a few species develop wart-like or hair-like nodules that can be mistaken for rhizines. Both upper and lower faces possess a true cortex —a layer of tightly packed fungal cells. On the upper side these cells are arranged in a pseudoparenchymatous tissue and often contain brown pigment near the surface. An overlying film of dead, compressed cells (the epinecral layer ) is usually thin; when its cells collapse and trap air the surface appears dusted with a pale bloom ( pruina ), but in many species the layer remains compact and the thallus looks plain. Beneath the cortex lies a loose medulla of filamentous hyphae. The lower cortex mirrors the upper one in construction but its outermost cells are smaller, thicker-walled and usually pigmented brown. [4]
The photosynthetic partner is almost always the from the green algal genus Diplosphaera (class Trebouxiophyceae), specifically D. chodatii in most studied material; rarer reports of Myrmecia biatorellae and Protococcus dermatocarponis suggest some flexibility. Algal cells occupy a distinct band just under the upper cortex, leaving the medulla fungus-only. Sexual reproduction takes place in flask-shaped fruiting bodies (perithecioid ascomata) that are sunk into the thallus surface so that only their tiny pores are visible. Each perithecium lacks the dark protective cap ( involucrellum ) seen in many relatives; its wall is colourless except for a ring of pigment around the pore. Short sterile threads ( periphyses and periphysoids ) line the neck canal, but the longer filaments (paraphyses) found in many lichens are absent. The jelly that embeds the spore sacs stains weakly with iodine: it turns red in standard strength and blue when highly diluted, a behaviour known as hemiamyloidy. [4]
Each club-shaped ascus contains eight smooth, colourless ascospores that are single-celled and ellipsoidal; they lie irregularly rather than in neat rows. Asexual reproduction is handled by immersed pycnidia scattered across the surface; these produce rod-shaped conidia. Chemical spot tests and thin-layer chromatography have failed to detect acetone-soluble secondary metabolites, though some species show a distinctive iodine-positive (red) reaction in the hyphal walls, indicating a polysaccharide rather than an aromatic lichen product. [4]
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