Cap 0.5-1.0 cm broad, subpendulous, at first cupulate, becoming shell-shaped; margin incurved in youth, then decurved, entire except for a slit-like opening at the stipe attachment; surface striate-sulcate, minutely tomentose, at maturity sometimes developing bluish-grey spots; context membranous, translucent; odor and taste mild.
Lamellae consisting of gill-like, wrinkled folds, adnate, fairly well-spaced, often anastomosing, white, sometimes spotted bluish-grey in age; edges and faces minutely pruinose.
Stipe rudimentary, 1-3 mm long, 0.5 mm thick, eccentric in attachment, dark grey to blackish with a white, pruinose covering.
Spores 9-11 x 5-8 µm, triangular to pyramidal, thin-walled, hilar appendage not conspicuous, inamyloid; spore deposit not seen, presumably white.
Solitary, scattered, or in rows on dead branches of herbs and shrubs, e.g. blackberry canes, California hazelnut, sedge culms, etc.; fruiting from late fall to mid-winter; restricted to moist, shaded habitats; known from coastal locations, possibly present at lower elevations of the Sierra Nevada; uncommon; easily overlooked.
Unknown, too small to have culinary value.
Tetrapyrgos subdendrophora resembles a tiny white oyster mushroom. Its defining characters, best seen with a hand lens, include gills that are reduced to anastomosing folds and a rudimentary eccentric stipe. A helpful fieldmark is the tendency of caps to develop bluish-black spots in age. Microscopically, the unusual triangular to pyramidal shaped spores are useful in confirming an identification. Tetrapyrgos subdendrophora is sometimes confused with Marasmiellus candidus which also has a white striate-sulcate cap, and also occurs on blackberry canes. The latter, however, is larger, the caps up to 2.5 cm broad, and often develop pinkish tones. Additionally, the stipe is usually central in attachment and better developed. Crepidotus species likewise bear a resemblance, but have true, typically closely spaced gills and ochre-brown spores. Another small, lignicolous, pleurotoid taxa, Cheimonophyllum candidissimus, can be distinguished by true gills that are more closely spaced.