Cap 1-3 cm broad, obtuse-conic, expanding to convex, sometimes with a low umbo; margin at first incurved, later decurved to level, hung with greyish-brown veil fragments; cap surface dingy-brown, granulose to powdered, darkest at the disc over a pallid ground color; context thin, ~2 mm at the disc, white, slowly pinkish when exposed; odor and taste sharp, somewhat astringent.
Gills free to barely attached, close, in youth bright vinaceous-pink, becoming pinkish-brown, eventually deep vinaceous-brown; gills up to 4 mm broad at the disc; edges even; lamellulae in three to four series.
Stipe 2-4 cm tall, 2-3 mm thick, round, spindly, fragile, straight to occasionally bent, more or less equal, in age hollow or with a pith-like core; surface when young, covered with greyish-brown powder or granules, easily rubbed off exposing a vinaceous-brown under-layer; stipe base forming a soil-encrusted bulb; partial veil evanescent, fragile, a greyish, granulose membrane, leaving fragments on the cap margin.
Spores 4.5-6.5 x 2.5-3.0 µm, elliptical to oblong-elliptical in face-view, similar in profile with a slightly flattened and curved side; smooth to minutely roughened, thin-walled, hilar appendage inconspicuous; spores olive-grey in deposit when fresh, brown when dry.
Solitary, scattered, or in small groups in humus-rich soil and near rotting wood; under both conifers and deciduous trees; also reported in greenhouses and on compost heaps; fruiting after fall rains along the coast, occasionally from fog drip in late summer; rare.
Melanophyllum haematospermum is a rare, small brown mushroom with striking pinkish-vinaceous gills and a distinctive granulose cap decorated with marginal veil fragments. Like Agaricus, a distant relative, the gills are free and a partial veil is present. However, the spores are olive-grey when fresh (brown when dry) not purple-brown as in Agaricus. The olive spore color is suggestive of Chlorophyllum molybdites, while the granulose to powdery cap hints of a relationship with Cystoderma. Both genera like Melanophyllum belong in the family Agaricaceae. Melanophyllum haematospermum should be compared with a number of unrelated mushrooms with pinkish to vinaceous gills. These include some diminutive members of Pluteus, Dermocybe, Entoloma, Psathyrella, Hygrocybe, Tubaria, and Agaricus. All of these can be distinguished by attached gills except for Pluteus, which lacks a partial veil and Agaricus which does not have a granulose cap.