We describe Umbilicaria nodulospora, a distinctive new species occurring on steep rock faces on old lava flows in California and Oregon. The species is unusual among lichenized ascomycetes in consistently having one or two shallowly bulging knobs at one end of each ascospore, suggesting a T, Y, or L shape; otherwise they are consistent with the appearance of ascospores in most Umbilicaria species. The species is readily distinguished in the field by a grayish tone to the brown upper surface, in combination with a thickly rhizinate lower surface. Distinctiveness of the species was supported by analysis of the ITS and LSU regions of nrDNA. No close relative or sister taxon was found. Umbilicaria nodulospora is so far known only from geologically recent flood basalts in central Oregon to northeastern California.