Description.Thallus thin (but typically on other crustose species with thicker thalli), dark grey or brownish, areolate; areoles to 0.50-0.65 mm wide; surface plane, matt; margin indeterminate; prothallus lacking; vegetative propagules present; consoredia dark brown or blackish, spreading from areole margins, usually giving the thallus a dark appearance, 20-40 in µm diam. Apothecia broadly or narrowly attached, frequent but rarely contiguous, to 0.30-0.60 mm in diam; disc dark brown, becoming black, persistently plane; thalline margin concolourous with thallus, entire, persistent, with or without consoredia, ca. 0.10 mm wide; excipular ring present, confluent. Apothecial Anatomy. Thalline exciple 60‑70 µm laterally, cortex ca. 10 µm wide; epinecral layer absent; crystals absent in cortex and medulla; cortical cells to 6.0-7.0 µm wide, pigmented brown; algal cells to ca. 12.5 µm long; thalline exciple 70-80 µm below; cortex 10-30 µm below, cellular to somewhat columnar; proper exciple ca. 10 µm wide laterally, expanded to 25-40 µm above; hypothecium colourless, 80‑90 µm deep; hymenium ca. 80 µm high, not inspersed; paraphyses 2.5-3.0 µm wide, not conglutinate, with apices to 3.5-6.0 µm, forming a dark red‑brown epihymenium; asci ca. 70 x 23 µm. Ascospores 8/ascus, development often asynchronous, sometimes 4-spored, Type A development, Milvina-type, (15.5-)18.0‑19.0(-21.5) x (8.0-)9.5‑10.5(-12.0) µm, l/b ratio 1.8-2.0, becoming constricted, walls thickened at septum and apex at first (Physcia-like), apices becoming thin walled (Physconia-like); torus well developed; walls ornamented (x1250), sometimes with faint pigmented bands around cells. Pycnidia immersed; conidiophores type I; conidia bacilliform, 3.0-4.0 x 1.0 µm.
Chemistry. Spot tests all negative; secondary metabolites not reported (Mayrhofer and Leuckert 1985).
Substrate and Ecology. Lichenicolous on crustose saxicolous lichens, usually Aspicilia species and sometimes becoming independent. Collected on granite, schist and serpentine at elevations of 1,090-2 700 m.
Distribution. The species is found in interior western North America and the Coastal Ranges of California. In Europe it has a mainly Mediterranean distribution although the type is from a maritime locality on the west coast of France. Giralt (2001) reports R. obnascens as being rather frequent in Spain where it occurs at high elevations in the mountains and lower in coastal regions. It also known from Switzerland (sterile, Mayrhofer 1984a) and has recently been reported from inland Sweden (Nordin 2004), a locality perhaps more comparable with its upland distribution in western North America.
Notes.Rinodina obnascens is a very distinctive species differing from R. milvina in its external morphology, characterized by its dark brown consoredia on a grey-brown thallus and lichenicolous on other crustose, saxicolous lichens. The vegetative propagules are described as ‘isidiös-schorfig’ by Mayrhofer and Poelt (1979) but they are very small and spherical, and are better described as consoredia (Tønsberg 1992). They are distinct from those of other consorediate saxicolous Rinodina species in North America in being very darkly pigmented.
The spores are almost identical in size to those of R. milvina but retain the septal and apical wall thickenings for longer during development. They are clearly related to the Physcia- and Physconia-type and appear to link these spore types to the Milvina-type. This relationship is strengthened by red-brown epihymenium that these spore types have in common.
Specimens examined. U.S.A. CALIFORNIA. San Luis Obispo Co., Cuesta Ridge, 1972, L. Segal (ASU); San Mateo Co., Jasper Ridge, S.C. Tucker 6349a (SBBG). COLORADO. Boulder Co., Boulder Canyon, 1977, R.A. Anderson (COLO); Gilpin Co., SSE Rollinsville, 1977, J. Poelt; R.A. Anderson (both GZU); Jefferson Co., Evergreen, J.W. Sheard 4693 (SASK); Summit Co., N Star Mountain, 1977, R.A. Anderson (GZU). MONTANA. Deer Lodge Co., Storm Lake, 1976, W.A. Weber (COLO). OREGON. Harney Co., Stinkingwater Pass, B. McCune 27835 (personal herb.). SOUTH DAKOTA. Fall River Co., Battle Mountain, C.M. Wetmore 10805 (MIN, MSC, UPS).