Thallus effuse, immersed, rarely visible between the grains of the substratum (coarse sandstone), when visible creamy-white without a well-developed cortex, a few brown pigmented cortical cells sometimes visible in microscopic section; usually covering relatively large areas (to 15-20 cm diam.). Medulla weakly IKI+ blue to red-purple. Photobiont chlorococcoid, cells (9-)12-15(-18)Ám diam.
Apothecia scattered, black or dark brown, lecideine, superficial, strongly constricted at the base, (0.8-)1.0-1.4(-2.0)mm diam., ▒flexuose when mature; disc flat, usually white pruinose, more so when young, black or slightly brownish, brown when wet; proper exciple black, persistent and slightly raised, 0.1mm wide. Hymenium hyaline, 120-135Ám tall; epihymenium brown, 12-20Ám wide. Paraphyses 1.5-2.5Ám thick swelling at apex to 5.0Ám, with brown pigmented cap; simple, occasionally branched towards the apex, septate, becoming moniliform towards apex, readily separating in water, IKI+ very pale purple. Asci cylindrical, c. 85-100 x 17-20Ám, outer walls IKI+ blue, contents IKI+ red-brown, without a tholus, Schaereria-type, dehiscing by a simple split in the outer wall, ascospores hyaline, 8/ascus, ▒uniseriate in ascus, broadly ellipsoid to sub-globose (14.0-)15.0-17.0(-20.0) x (8.5-)10.0-12.0(-13.5)Ám, length/breadth ratio 1.2-1.7. Hypothecium composed of randomly arranged hyphae, hyaline above, becoming pale to mid- brown below, 70-80 Ám high, merging into the dark-brown, horizontally arranged hyphae of the excipulum that extends below the hypothecium. Excipulum cupular, extending below the hymenium and hypothecium as horizontally arranged, dark brown pigmented hyphae, 170-250Ám high; laterally with a c. 100Ám wide pale brown inner zone of radiating hyphae c. 3.5Ám wide and a dark brown outer zone c.80Ám wide composed of isodiametric cells 8-12Ám across; interspersed with large groups of crystals clearly visible under polarized light.
Conidiomata pycnidia, not frequent but usually present, black, immersed, 0.15-0.2mm wide, walls dark brown. Conidia simple, cylindrical c. 3.5 x 0.8Ám, arising from elongated, simple, conidiogenous cells, Type II of Vobis (1980).
Chemistry: Thallus and apothecia C-, K-, KC-, Pd-; unidentified fatty acid detected by TLC.
Distribution and Ecology. Schaereria porpidioides is known only from the Falkland Islands and Isla de los Estados. From the collection details it appears to be a species of exposed siliceous rocks. No vascular plants or bryophytes are present on the specimens and associated lichen species are few but include Neuropogon fasciata (Du Rietz) Lamb, Pertusaria spegazzinii MŘll. Arg., Poeltidea perusta (Nyl.) Hertel & Hafellner and Rhizocarpon geographicum (L.) DC.
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