Montana Field Guide

Thallus foliose, umbilicate, roundish to broadly and irregularly lobed, mostly less than 10 cm in diameter, rather fragile when dry; margins often perforate and lacerate; upper surface gray, gray brown, to blackish, partially grayish to white pruinose, especially on reticulate ridges near the umbilicus, the ridges fading radially, distinct or weak; lower surface light tan near umbilicus, dark gray brown toward the margins, with sooty black patches (from thalloconidia); sooty black rhizines often present, frequently in tufts, sometimes the tufts protruding upwards through holes in the surface; soredia and isidia lacking; apothecia rare (McCune and Geiser 2009).

U. havaasii can form fluffy colonies on rock, in contrast to the more appressed growth form of many Umbilicaria species. Up close, U. havaasii is distinctive in the combination of sooty black areas on the lower surface and subtle to distinct perforations near the lobe margins (McCune and Geiser 2009).

On siliceous (noncalcareous) rock.

May reproduce sexually by spores from the apothecium.

None identified.