Basidiomata: sessile, solitary or imbricate and united in rosettes up to 20 cm or more in diam. (to over 60 cm across the longer axis in some specimens, but mostly under 5 cm across in Sonoran region material); the individual pilei (bracket-like units) flabelliform, semicircular, or reniform, rarely almost stalked, frequently laterally fusing, 1-6 (-8) x 1-6 (-8) cm across (mostly 1-2 cm across in our material), thin, 0.18-1.2 (-1.4) mm, membranaceous or almost paper-like, brittle when dry upper surface: usually distinctly and densely but shallowly sulcate-zonate (but in our material rather plane and even but sometimes with fine, concentric wrinkles), without radial fibrils, smooth, under a lens slightly villose (appearing faintly powdery-roughened), in live state glossy blue-green or greenish blue, in herbarium becoming creamy white to whitish gray, grayish yellow, or (especially outside the Sonoran region) grayish green, gray-blue-green, blue-green, or bluish gray, in central part usually darker, the outer 2-3 mm usually ochraceous-cream-colored (more yellowish than rest of upper surface), or greenish or ink-green at the edge margin: usually with few and coarse, rounded lobes, acute (thinning towards edge), at the edge when dry narrowly but strongly involute downward photobiont: a "Chroococcus" (Rivulariaceae); cells: green or yellowish, irregularly ellipsoidal or almost polygonal, oblong, (8-) 10-15 um long, without a mucous shell; forming a layer c. 150-200 um thick lower surface: densely concentrically zonate, gray to greenish or blue-gray (somewhat darker than upper surface), under a lens appearing granulose or faintly white-arachnoid hymenophores: at first scattered, 0.2-0.4 mm, then up to 1 mm diam. and 0.3-0.6 (-1) mm high, 1-2 mm distant from each other, irregularly cup-like or apothecium-like, later uniting to form interrupted concentrical ridges, finally polygonally or almost reticulately cracked; surface initially deep cream color, then pale ochraceous or dull yellowish-grayish-reddish; in old specimens the hymenial spots fall away beginning from the margin and thus the lower surface becomes sterile again basidiomata anatomy: context (hyphal mass between upper surface and subhymenium): layered; subhymenium: (30-) 50-150 (-200) µm thick; hymenium: consisting of very numerous basidioles and scattered basidia; basidioles: 4-7 µm diam. hyphae: without clamps basidia: often few or absent, 15-20 (-25) x (5.5-) 6-8.5 µm; sterigmata (spore-bearing projections): 4 or rarely 2, slightly subconical, 5-7.5 µm long, soon collapsed basidiospores: often few and in poor condition, ellipsoid-teardrop-shaped, slightly boat-shaped, with lateral apiculus (projection for attachment to the sterigma), without droplets, (6.5-) 7.5-8.5 x (3.8-) 4-4.5 (-5) µm; spore print: white Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on soil or mosses (sometimes over acidic rocks) and trees, rarely on bare loam; in sheltered to rather sunny and arid habitats World distribution: U.S.A. (Florida, Hawaii); widely distributed in southern to north-central Mexico, Central America, the Caribbean, and South America; Africa (Mauritius Island, E of Madagascar); early reports (Berkeley and Curtis ) from "west Africa" and the Indian subcontinent ("Hindustan") need to be confirmed Sonoran distribution: Chihuahua (2000-2300 m) and occasional in Sinaloa (1700 m), generally on shaded, mossy acidic rocks (often rhyolite) in pine-oak forests. Notes: The internal anatomy of this species is described more fully by Parmasto (1978). As discussed in that treatment, although this species (over its full distribution range) is highly variable, especially in the color of the upper surface and in the external structure of the hymenium, the microscopic characters are much more uniform, and most apparent variations in the spores reported in the earlier literature [e.g, 10-15 x 6-12 µm, given by Fink (1935)] are based on extraneous spores or conidia from other fungi. The basidiomata in our material tend to be rather small, and with a rather paler and smooth upper surface, but fall well within the range of variation exhibited by material from other areas. This species is similar to D. sericeum (which occurs further south in Mexico) in the bracket-like (not crustose) form and lack of clamp connections, but D. glabratum differs by the densely sulcate-zonate upper surface, lack of radial fibrils, and narrowly but strongly involute margin of the basidiocarp, and photobiont not Scytonema.