Lecidella greenii
Lecidella greenii is a species of lichen-forming fungus in the family Lecanoraceae. The lichen forms whitish to pale grey crusts up to 5 cm across on granite rocks, with small black fruiting bodies that occur in dense clusters. It grows both on exposed rock surfaces and within natural rock cracks in ice-free areas of Victoria Land, particularly in coastal sites influenced by fog.
Taxonomy
Lecidella greenii was formally described in 2008 by Ursula Ruprecht and Roman Türk from material they collected at Granite Harbour in the Transantarctic Mountains of Victoria Land.The species is one of only two members of Lecidella known from continental Antarctica, and it conforms to the genus through its small black, apothecia and the presence of Lecidella-type asci, that distinguish the group from superficially similar crustose genera such as Lecanora and Lecidea.The epithet honours the New Zealand botanist T.G. Allan Green. Within Lecidella, the combination of a strictly rock-dwelling lifestyle, broadly ellipsoid, non-septate spores averaging 10–11 micrometres long, and the presence—in one of two chemotypes—of the stictic acid complex sets L. greenii apart from other members of its genus.
A 2012 molecular study of Antarctic Lecanoraceae placed Lecidella greenii in a distinct, well-supported lineage that is sister to the combined L. patavina/''L. stigmatea group and to the bipolar species L. siplei. The same analysis, which sampled 90 specimens along a Ross Sea transect, recovered seven major clades in the family and suggested that roughly 75% of the region's lichens are endemic to continental Antarctica—evidence that reinforces L. greenii''s status as a locally confined species.
Description
The thallus forms a well-developed, crustose film that appears whitish to pale grey-beige and may occupy patches up to five centimetres across. Its surface is cracked into small polygonal and, in places, becomes minutely ; individual areoles or granules rise no more than a millimetre above the rock. The lichen grows both within natural fissures of the granite and on the exposed surface. Black pycnidia are rare and inconspicuous; they provide an asexual means of reproduction. The is a green alga assigned to Trebouxia, whose cells are dispersed throughout the upper portion of the thallus.Apothecia occur in dense clusters and enlarge with age from flat to modestly convex up to about 1.2 mm in diameter. When young they show a thin, pale rim that soon becomes lost beneath the expanding black, disc. Microscopic examination reveals an olive-green overlying a colourless hymenium 80–90 μm tall that becomes lightly brownish at maturity and is suffused with minute oil droplets. Paraphyses are, flexuous threads 1–2 μm wide whose tips swell slightly and accumulate the same dark pigment that colours the upper disc. The hymenial gel does not stain with iodine, and spot tests give variable K reactions but remain negative for C. Each Lecidella-type ascus contains eight hyaline spores that lack internal walls ; they are broadly ellipsoid, typically 10–11 μm long by 6–7 μm wide, yielding a length-to-width ratio of about 1.5. Two chemotypes have been detected: one apparently lacks secondary metabolites, while the other produces the stictic acid.