Fruiting body 4-6 mm tall, 4-5 mm broad, cylindrical, if flaring, abruptly at the apex; outer surface, white, pubescent when young, becoming buff to pale-grey, matted when senescent; mouth fringed, the opening covered by a thin, white, evanescent, cottony membrane (epiphragm), when lost, revealing a glabrous, tan interior and small, brown, peridioles (eggs), 0.5-1.0 mm in diameter, embedded in a mucilaginous gel.
Spores 6.5-8.5 x 4.5-5.5 µm, broadly ellipsoid to amygdaliform, smooth, thick-walled, hyaline, hilar appendage not evident.
Scattered to clustered on sticks, wood chips, and other woody debris, both coastal and montane; fruiting from mid to late winter, old fruiting bodies persisting for months; common.
Unknown; too small and tough to be of culinary value.
Nidula niveotomentosa is easily recognized when young by its pubescent, white, cylindrical fruiting bodies and small brown peridioles embedded in mucilaginous gel. Older specimens may be matted, pale-grey to brown, leading to confusion with Nidula candida. The latter, despite the species name which means "white," is actually greyish to brown, and shaggy to finely squamulose when young. Nidula candida is also larger, up to 15 mm tall, 8 mm broad, and has a fruiting body that flares broadly at the mouth. Both species are common, but Nidula candida is more northern in distribution. Species of Cyathus and Crucibulum also bear a resemblance to Nidula tomentosa but can be distinguished by peridioles that are attached to the cup wall by a thin cord (use hand lens) rather than embedded in a mucilaginous gel.