VICTORIA. Rubicon, Royston road, hypogeal in wet eucalyptus forest, 20 May 1974, K. & G. Beaton', Otway Range, Apollo Bay end of Turtons Track, hypogeal in wet eucalyptus forest, 27 Sept. 1982, K. & G. Beaton 58.  TASMANIA. Hobart, underground, Rodway 609 (type K).

Gasterocarp 1-2 cm diam., globose, ellipsoid or irregular, basally attached. Peridium about 1 mm thick, dingy white, drying light greyish brown, smooth, not viscid. Gleba light brown, drying darker, loculate, of globose or ellipsoid, empty or partially full chambers, with some radial arrangement. Tramal plates 100-150 µm thick, hyaline or pale brownish, consisting of a broad hymenophoral trama and poorly developed subhymenial layers; clamp-connexions present on all hyphae. Sterile base scarcely developed or absent.
Spores 13-16 x 7.5-8.5(14 ± 0.7 x 8 ± 0.5) µm (excl. myxosp.), Q = 1.75; obovoid to narrowly limoniform, often but not always with a mucronate apex, golden brown, with a thickened wall bearing a fine verrucose ornamentation, overlaid by a loose, hyaline myxosporium which often becomes detached at the base and or the apex. Basidia 32-27 x 7.5-9.5 µm, clavate, bearing mostly two short, tapering, straight sterigmata, but also forms with one or four sterigmata present; also numerous, immature, ellipsoid basidia. Hymenophoral trama regular, hyaline, of parallel, thin-walled hyphae, 3-14 µm diam. Subhymenial layer narrow, 10-15 µm wide, interwoven or indistinctly pseudoparenchymatous. Peridiopellis up to 200 µm thick, consisting of a loose and disrupted epicutis, with erect or semi-erect, inflated clavate elements, 12-40 x 6-14µm, sometimes producing an indefinite epithelium.

Hymenogaster nanus is extremely similar, and closely related, to H. albus, but differences in the narrower spores, the lack of a true epithelium in the peridiopellis, a poorly developed subhymenial layer, and a paler coloured gleba, are sufficient to maintain a distinction between the two species.