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Dermatocarpon

Genus of lichen From Wikipedia, the free encyclopedia

Dermatocarpon
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Dermatocarpon is a genus of lichens in the family Verrucariaceae.[2] Members of the genus are commonly called stippleback lichens because they have fruiting structures called perithecia that are flask-shaped structures embedded in the nonfruiting body (thallus), with a hole in the top to release spores, causing an appearance of being covered with small black dots.[3]: 35  Its species are told apart chiefly by spore size, the colour and texture of the lower surface, and whether the epinecral layer gives a pruinose bloom.

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Description

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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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Ecology

Dermatocarpon typically colonises siliceous or calcareous rock in moist settings—river margins, seepage faces and shaded cliffs.[4]

Species

References

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