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Rinodina roscida (Sommerf.) Arnold
Family: Physciaceae
Rinodina roscida image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus thin, grayish white, continuously granular or of scattered granular verrucae of up to 0.6 mm diameter, dull or pruinose. Apothecia sessile, to 1 mm broad; margin of same color as thallus, to 1 mm wide, entire and persistent; thalloid exciple cellular laterally, lower part is of intricate hyphae obscured by oxalate crystals, cortex I—; proper exciple 10-20 μm, widening upward to 20-50 μm; disk black, more or less pruinose, flat or concave; hypothecium hyaline; epihymenium red-brown; hymenium 100-150 μm, hyaline; paraphyses 2.5-4 μm, tips 4.5-6.5 μm and pigmented brown; asci clavate; spores polarilocular with broad porus and angular locules, tips mucronate, 28-42 X 11.5-16.5 μm.

Reactions: thallus K—, C—, P—.

This species grows on calcareous substrata, on humus, soil, and rabbit or ptarmigan dung. It is a common circumpolar arctic-alpine species.

Sheard (unpubl. ms) considers this species well separated from R. turfacea by reason of the larger spores and the intricate rather than columnar lower cortex (clear with HN03).