TYPE: AUSTRALIA, Tasmania, Mt Wellington, Feb 1904, L. Rodway 1267 (holotype HO 89531; isotypes OSC, NY, FH). OTHER COLLECTIONS EXAMINED: NEW ZEALAND: COROMANDEL: Thames, Waiomu Valley, R. E. Beever 748, 29 Apr 1988 (PDD 48309); same locality and date, M.P. Amaranthus (Trappe 9904, 9905, 9906), (OSC), M.A. Castellano (Trappe 9895, 9897, 9898, 9903), (OSC), R. Young (Trappe 9887, 9899, 9900, 9901, 9902), (OSC). TAUPO: Tokoroa, M. Chu-Chou, 5 Apr 1979 (NZFRI 3287); Kaingaroa Forest, M. Chu-Chou, May 1982 (NZFRI 3289). TARANAKI: Egmont National Park, Kaitake Range, Lucys Gully, R. E. Beever 687, 16 May 1987 (PDD 48310, OSC). MID CANTERBURY: Christchurch, Victoria Park, R.E. Beever 1265, 20 Sep 1992 (PDD 60576). ECUADOR: Quito, L. Mille, Jan 1921 (type of H. eucalyptorum, NY, PDD 8309). FRANCE: Porquerolles, L. Riousset, 12 Nov 1980 (OSC, det. by Riousset as H. pterosporum).

Basidiomata up to 2.5 cm diam., globose to subglobose, ellipsoid or irregularly lobed, dull white with pale brown to pale reddish brown patches when fresh, drying dark brown except in recessed areas which are pale brown to almost white, surface smooth to mostly tomentose when fresh, wrinkled when dry, surface with adhering soil particles. Gleba olive grey to bright green when young, dark olive to almost black when mature and deliquescent; locules more or less radially elongate, partially to completely filled with spores. Rhizomorphs numerous, highly branched, attached at base, concolorous with peridium, associated with conspicuous white mycelium in soil. Columella dendroid, narrow, translucent. Taste nil to faintly peppery. Odour slightly perfumed to sharp after incubation. Peridium separable from gleba in large flakes, a single layer 140-150(-250) µm thick, of brown (near surface) or hyaline (near gleba), thin-walled, irregularly shaped, sometimes inflated hyphae, cells elongate to subglobose, up to 5 µm diam. near gleba, up to 12 x 25 µm diam. in mediostratum, with numerous minute crystals adhering to outer hyphae, clamp connections common. Trama 40-100 µm thick, of hyaline, loosely to compactly interwoven hyphae, 2.5-5 µm diam., in a gelatinised matrix, hyphae mostly elongate, sometimes with nodose ends, clamp connections absent; with suture-like structures traversing peridial trama in places. Basidia rehydrating poorly, hyaline, (4-)6-spored. Spores smooth, 9-12 x (3-)4-5 µm without utricle, 9-12 x 8-9 µm with utricle, ellipsoid; apex obtuse, base sessile, sometimes truncate; wall <0.5 µm thick. Utricle distinct, laterally inflated up to 2.5 µm, attached near base and below apex, commonly forming a cylinder around spore. Spore colour in KOH hyaline singly, pale green in mass.

Algeria, Australia, Ecuador, France, Italy, New Zealand, U.S.A. (California).

Habitat: hypogeous or subepigeous in plantations and modified communities, putatively mycorrhizal with Eucalyptus spp. including E. delegatensis, E. fastigata, E. nitens, E. regnans (Chu-Chou & Grace 1983). Season: April to September.

ETYMOLOGY: From Latin inflatus, swollen, referring to the greatly inflated spore Utricle.
REMARKS: The description includes data from the many Australian collections of the first author. Hysterangium inflatum is easily distinguished from all other species by its regularly inflated, barrel-like utricle, which gives the spore a winged appearance in optical section. Hysterangium inflatum appears to be a common ectomycorrhizal associate of Eucalyptus spp. and has evidently been introduced with Eucalyptus seedlings to many parts of the world.
In contrast to Beaton et al. (1985b), we regard Hysterangium tunicatum Cunningham as a distinct, albeit invalidly published, species. H. pterospermum is placed in synonymy after examining an authenticated collection.
The species was first recorded from New Zealand by Chu-Chou & Grace (1983). Their "Hysterangium sp. 3" [?locality, M. Chu-Chou, 6 Jul 1979 (NZFRI 3293)] appears also to be this species. The Zeller & Dodge (1929) record of H. inflatum from New Zealand was based on Cunningham collection "1189" (PDD 8318) now recognised as H. neotunicatum.

Type: Mycorrhizal Fungi; Description: Basidiomata subepigeous, subglobose, pyriform or irregularly lobed, white with reddish brown patches, up to 25 mm in diameter, with numerous rhizomorphs at the base; peridium composed of a single layer, brown in section. Gleba greenish at first, becoming dark olive green to almost black, composed of tramal plates anastomosing to form elongate locules, which are partially filled with basidiospores; columella branched. Basidiospores ellipsoid, 0-septate, 9–12 × 3–5 μm (without utricle), smooth, hyaline; utricle distinct, inflated laterally up to 2.5 μm, attached near the base and below the apex forming a cylinder around the spore.

Distribution: Coromandel, Bay of Plenty, Taranaki, Taupo, Mid Canterbury.; 1st Record: Chu-Chou & Grace (1982).

Significance: Shown experimentally to be a mycorrhizal partner of Eucalyptus saligna (Chu-Chou & Grace 1982).; Host(s): Eucalyptus delegatensis, E. fastigata, E. nitens, E. regnans.