Basionym:Lecidea spadicomma Nyl., in Crombie, J. Linn. Soc. Bot.15: 233 (1876); type: Chile, (XII Región de Magallanes y de la Antártica Chilena, Isla Wellington), Eden Harbour, in the bed of a stream, April 1868, R. O. Cunningham (BM—holotype; BM, E, H—isotypes).
Description:
Thallus thick, rimose-areolate, cream-brown to yellow-orange, sometimes mottled with alternating dark grey and orange parts; upper section composed of vertically orientated hyphae without an upper cortex but surface cells with a dilute brown pigmentation; medulla I+ violet. Photobiont chlorococcoid, cells 7–12 μm diam.
Apothecia 0·5–2·2mm diam., numerous, ±regularly scattered, innate, rounded,±flat or occasionally concave; proper margin not evident; disc dark brown to black, paler brownwhenwet. In section:proper exciple annular, poorly developed, not reaching the thallus surface, dilute brown, 15–20 μm wide, composed of narrow septate hyphae. Hypothecium dark brown, 90–105 μm tall, often extending up to 350 μm into the thallus, composed of vertically arranged hyphae that merge with the hymenium, less well organized at base. Hymenium 180–200 μm tall; paraphyses slender, c. 1μm thick, only slightly swollen at apex, branched and anastomosing; epihymenium 12–20 μm thick, pale brown (Arnoldiana-brown). Asci 70–60×20–25 μm, cylindrical-clavate, mature asci Porpidia-type; ascospores simple, hyaline (15·4–)23·0 ±3·64 (–32·5)×(6·0–)10·7 ±2·15(–15·6) μm; l/w ratio 1·7–2·6, mean = 2·20, (n = 111).
Conidiomata pycnidia, usually present, dark brown to black, 0·05–0·10mm diam., immersed in the thallus, most frequent along the thallus margin adjacent to other thalli; conidia hyaline, filiform, (18–)25–30 × 1 μm (n = 10).
Distribution and ecology. The distribution of X. spadicomma, with three widely separated localities between the Falkland Islands (where it is common) to northern Patagonia, suggests that it is a widespread species in the area, although its absence from the extensive collections made from western Patagonia and Fuegia (Isla Grande and Isla de los Estados) by Imshaug and co-workers (Fryday & Prather 2001) is surprising. Xenolecia spadicomma is primarily a species of semi-inundated streamside rocks (Fig. 5), although it has also been collected from mountain summits (Imshaug 41549) and in rainwater-collecting depressions in otherwise dry rocks (Fryday 11355).