Cresponea graemeannae


Cresponea graemeannae is a species of saxicolous crustose lichen in the family Opegraphaceae, described in 2020 from Tasmania, Australia. It forms very thin, patchy films on sandstone or dolerite and bears small, black, disc-like fruiting bodies with a thick, radially split margin. The species is set apart from related taxa by its almost inapparent thallus, thin greyish bloom on young fruiting body, a margin that reacts green in potassium hydroxide solution, an oil-dotted tissue beneath the spore layer, and thick-walled ascospores with between five and nine cross-walls.

Taxonomy

Cresponea graemeannae was described by Gintaras Kantvilas in 2020 on the basis of collections from Tasmania's east coast; the holotype is from Spring Bay Mill at low elevation in coastal Allocasuarina woodland. The name honours Graeme Wood and Anna Cerneaz for supporting the field expedition during which the species was discovered.

Description

The thallus is absent or extremely thin, appearing only as a greenish to faint pink-green discolouration of the rock, often forming extensive but ill-delimited patches up to about 30 cm across; the photosynthetic partner is a alga. Apothecia are 0.7–2 mm wide, somewhat narrowed at the base and sometimes nearly stalk-like. The is brown-black to black, with a very thin pale-grey when young, becoming plane to slightly convex and sometimes losing the pruina with age; some old discs may develop a sterile central "plug". The margin is thick, strongly inrolled and conspicuously split radially; in section it is opaque dark brown and turns greenish in potassium hydroxide solution. The is hyaline to pale yellowish and characteristically filled with oil droplets; the hymenium is 80–110 micrometres thick, the uppermost part turning olive-yellow in KOH.
Asci are of the abietina type typical for the genus; are capped and slightly pigmented at the tips. Ascospores are, 5-9-septate, typically 25–40 × 6–8 μm, with walls up to about 2 μm thick. Black, superficial pycnidia produce small to fusiform 4–6 × 1–1.2 μm. No lichen products were detected by thin-layer chromatography.

Similar species

Within Cresponea, the new species was compared most closely with the corticolous C. plurilocularis and C. subpremnea. It differs from C. plurilocularis by its rock habitat, thicker and radially fissured apothecial margin, a hypothecium packed with oil droplets, and by having the disc only thinly pruinose when young; C. plurilocularis has a better-developed thallus, smaller apothecia with a thinner, usually entire margin, and the disc is more often persistently yellowish-pruinose. From C. subpremnea it differs in having shorter, broader spores, an hypothecium, and the conspicuously fissured margin. Among the few other rock-dwelling members of the genus, C. ancistrosporelloides from Western Australia has a well-developed thallus and distinctive tail-like spores, and the Northern Hemisphere C. premnea var. saxicola has smaller, less septate spores—both unlike C. graemeannae.

Habitat and distribution

Cresponea graemeannae occupies shaded, sheltered microhabitats on vertical and overhanging rock faces – especially clefts and underhangs – on relatively soft, coarse-grained Triassic sandstone along a short, roughly 300 m band of sea-cliff woodland dominated by Allocasuarina verticillata on Tasmania's east coast. It can form large patches but was found in only six, well-spaced populations in the type area. Associated saxicolous lichens in this habitat include, for example, Buellia halonia, Diploicia canescens, Porina species, Verrucaria fusconigrescens, and others. A further, smaller collection was made about 100 km to the north on Jurassic dolerite underhangs in sclerophyll scrub. The species appears to be rare and, so far, localised to coastal eastern Tasmania.