Type. U.S.A. NEW MEXICO. Near Las Vegas, 1927, Arsène Brouard, s.n. (UPS ‑ lectotype here designated!, W - isotype!).
Description.Thallus mostly thin, dark grey or ochraceous, areolate; areoles irregular, sometimes with raised margins, to 0.60‑1.00 mm wide; surface plane, matt; margin indeterminate, prothallus absent; vegetative propagules absent. Apothecia innate, becoming broadly attached, frequent, often occupying the whole of smaller areoles, sometimes contiguous, to 0.30‑0.70 mm in diam.; disc black, plane, sometimes becoming slightly convex; thalline margin concolourous with thallus, to ca. 0.05 mm wide, entire, sometimes becoming excluded; excipular ring absent. Apothecial Anatomy. Thalline exciple 75-100 µm wide laterally; cortex 5-10 µm wide; epinecral layer 10-20 µm wide; crystals absent in cortex and medulla; cortical cells to 4.0-6.5 µm wide, pigmented or not; algal cells to 12.5-23.0 µm long; proper exciple ca. 10 µm wide laterally, expanded to 20‑35 µm at periphery, hyaline; hypothecium hyaline (40‑)60-100 µm deep; hymenium 80‑100 µm high, not inspersed, paraphyses 1.5-2.0 µm wide, not conglutinate, apices expanded to 4.0-5.5 µm wide, darkly pigmented and immersed in dispersed pigment to form a brown or dark red‑brown epihymenium; asci 40‑55 x 16-19 µm. Ascospores 8/ascus, Type A development, Dirinaria‑type, (15.0-)18.0-18.5(-22.0) x (7.5-)8.5-9.0(-10.0) µm, average l/b ratio 2.0-2.2, lumina Physcia-like, apical walls remaining thick, endospore wall finally becoming pigmented, larger spores swelling at septum in KOH; torus present in some spores, narrow; walls faintly pitted or not. Pycnidia not seen.
Chemistry. Spot tests all negative; secondary metabolites not detected.
Substrate and Ecology. On sandstone (sometimes calcareous) rocks in xeric habitats.
Distribution. A rare North American endemic species found on the east slope of the Rocky Mountains from Wyoming to New Mexico (Figure 30). The outlier in the Channel Islands of California must be suspect but the specimen could not be placed in any other species.
Notes. The Dirinaria‑type spores suggest that R. brouardii is related to R. gennarii and the general habit of the two species may be quite similar. They are distinguished by the innate apothecia in early development and larger spores of R. brouardii. Specimens with innate apothecia are similar in habit to R. innata, a species which is distinguished by its shorter Physcia-type spores.
Specimens examined. U.S.A. CALIFORNIA. Santa Barbara Co., Santa Cruz Island, 1988, C.C. Bratt, 5707 (SBBG). COLORADO. Elbert Co., 4mi NW River Bend, 1955, S. Shushan 7994 (COLO). NEW MEXICO. San Juan Co., Chaco Wash, 1979, T.H. Nash 16285 (ASU); San Miguel Co., Las Vegas, 1927, A. Brouard (M, UPS). WYOMING, Platte Co., Guernsey, 1957, D.B. Parkinson S9219, S9225 (COLO).