Menegazzia castanea

Detailed description

Thallus firmly attached at margins, ± loosely attached centrally, forming radiating, regular rosettes, often becoming irregular and coalescing to cover extensive areas of substrate, to 20 cm diam., saxicolous, sometimes spreading over soil and adjacent lichens and mosses. Lobes numerous, marginally radiating, rather regular, small to medium, 2-4 mm wide, often obscured centrally by numerous, short, imbricate, congested lobules, margins contorted, entire, often notched, often, extensively blackened, pigment spreading to centre of lobes, hollow, markedly inflated, lower side of internal cavity black. Upper surface pale grey-brown or fawn, apices and sometimes lateral lobes suffused brownish, ± maculate, with black or dark brown lines or patches, often denser centrally (×10 lens), smooth or puckered (especially centrally), shining and faintly white-maculate or reticulate towards lobe ends, sorediate. Perforations sparse to scattered, small, 0.2-0.5 mm diam., rounded or irregular, margins not elevated. Soralia pustular, arising as swellings on upper surface with eventual rupture and folding back of cortex to form coarse or finely abraded, efflorescent, proliferating, granular-sorediate clusters, coalescing centrally, soredia greyish-fawn, pale when abraded. Lower surface black, brown or red-brown marginally, extensively puckered. Apothecia rare, scattered or contiguous in groups, small, 2 mm diam., adnate, cupuliform, margins elevated, crenulate-striate, disc red-brown to brown, epruinose. Epithecium pale red-brown or brown, with numerous small granules. Hymenium c. 100-130 µm tall. Asci 2-spored. Ascospores ellipsoid, 39-44 × 21-23 µm.

Chemistry: Medulla K+ yellow-orange, C−, KC+ orange, Pd+ orange; containing stictic, constictic and menegazziaic acids and accessory compounds.