Basidiomata up to 1 cm diam., subglobose to irregularly lobed, white, bruising brown when fresh, dark brown with pale brownish white areas when dried, surface wrinkled when fresh. Gleba firm, cartilaginous, dark green; locales irregular, partially filled, some contiguous with peridium. Rhizomorphs few, small (<1 mm diam.), attached to base, concolorous with peridium. Columella much reduced, dendroid, translucent. Taste not noted. Odour nil. Peridium not separable from gleba, a single layer 400-450 µm thick, of thin-walled, irregularly inflated hyphae, 20-35(-40) µm diam., smaller and more or less periclinal near gleba and peridial surface, outer portion (100-150 µm) golden brown and encrusted with soil particles, inner portion (250350 µm) hyaline without incrustations, clamp connections absent. Trama up to 80 µm thick, of hyaline, thin-walled, interwoven hyphae, 3-4 µm diam., in a gelatinised matrix, clamp connections absent. Basidia not observed. Spores minutely to moderately verrucose, 18-20(-22) x 6-7 µm, ellipsoid to fusoid, some asymmetric; apex acuminate to mostly papillate, base with a sterigmal attachment 1 µm long x 2 µm wide; wall 1-1.5 µm thick, thicker at spore apex. Utricle wrinkled, adherent, up to 1 µm thick. Spore colour in KOH pale green singly, olive brown in mass.

New Zealand.

Habitat: hypogeous in podocarp-broadleaf forest, probable mycorrhizal associates uncertain. Season: April.

Basidiomata usque ad 1 cm diam., subglobosa vel irregulariter lobata, maxime firma, alba, contundentibus brunnea, minime rugosa. Gleba firma, cartilaginea, obscure viridis, loculis irregularibus, partialiter repletis. Rhizomorphae paucae, basi affixae, peridio concolores. Columella multo deminuta, dendroidea, translucens. Peridium non separabile, 400-450 µm crassum, hyphis irregulariter inflatis, 20-35(-110) µm diam., prope paginam aureo-brunneis, prope glebam hyalinis. Trama usque ad 80 µm crassa. Sporae minute vel moderate verrucosae, 18-20(-22) x 6-7 µm, ellipsoideae vel fusiformes, aliquot asymmetricae, apice acuminato vel pro parte maxima papillato; paries 1-1.5 µm crassus; utriculus rugosus, usque ad 1 µm crassus; singulariter pallide virides, aggregate olivaceo-brunneae. Holotypus PDD 60093.

ETYMOLOGY: Named for the collector of the type, Roy Young of Grants Pass, Oregon.
REMARKS: Known only from the type collection.
Hysterangium youngii has the largest spores of any Hysterangium species in New Zealand. It resembles H. salmonaceum Beaton, Pegler & Young from Australia in spore size and shape, but can be distinguished by its ornamented spores.

TYPE: NEW ZEALAND, COROMANDEL, Thames, Kaitarakihi Track, R. Young (Trappe 9878), 28 Apr 1988 (holotype PDD 60093; isotype OSC).