Since Vittadini first described Hymenogaster in 1831, a heterogeneous
assemblage of truffle-like Basidiomycetes has been assigned to the gen
us. As a consequence, the boundaries of Hymenogaster became inflated e
ven beyond Vittadini's original broad concept, and the genus came to r
epresent more than one phylogenetic line. This paper clarifies the gen
eric limits of Hymenogaster and challenges a prevailing notion that Hy
menogaster represents the hypogeous member of a phylogenetic line link
ed through Thaxterogaster to Cortinarius. On the basis of both macromo
rphological and micromorphological characters of basidiomes, Hymenogas
ter sensu stricto is redefined. Selected species are allocated to four
new genera: Cortinomyces, Descomyces, Quadrispora, and Timgrovea. A k
ey to these genera is provided. Four of the eight original Vittadini s
pecies are excluded from Hymenogaster H. rufus (type lost), H. citrinu
s (to Gautieria), H. luteus (to Hysterogaster), and H. niveus (to Cort
inomyces). The remaining four species have large, thick-walled, broad
ellipsoid to fusiform spores bearing a large, cupped hilar appendix an
d are designated as the core of Hymenogaster since they include the ty
pe species H. bulliardi. Also included with the type are H. olivaceus,
H. lycoperdineus and H. griseus. The relationships of these Hymenogas
ter species to other fungi are not known, but the spore type does not
indicate a close relationship with Cortinarius and Thaxterogaster. The
remaining Vittadini species H. niveus is placed in the new genus Cort
inomyces by virtue of its smaller, warty spores. Cortinomyces is large
ly distinguished from Hymenogaster by having cortinarioid spores. Nume
rous other characters, such as peridial pigments and structure, sugges
t that Cortinomyces fits into a phylogenetic series with Thaxterogaste
r and Cortinarius. Hymenogaster cribbiae, H. effodiendus, H. luteus (n
on Vittadini), H. niveus, H. purpureus, H. violaceus, and H. viscidus
are recombined to Cortinomyces. Descomyces has distinctive spore morph
ology (e.g., a smooth rostrum and ornamentation embedded in the perisp
orium) and peridium structure (e.g., two layered and with swollen cell
s). This peculiar combination of peridial and spore characteristics al
so occurs in Setchelliogaster and in Descolea. It is proposed that Des
comyces (with hypogeous angiocarpic basidiomes and a loculate hymenium
) represents the truffle-like form in a phylogenetic series that also
includes Setchelliogaster (subhypogeous, pseudoangiocarpic basidiomes)
and Descolea (epigeous bivelangiocarpic basidiomes and a lamellate hy
menium). Further supporting evidence of this relationship is obtained
from examination of mycorrhizae and axenic cultures of these fungi. Sp
ecies transferred to Descomyces include H. albellus, H. albus, and H.
javanicus. H. albellus and H. albus are maintained as separate species
, the former is considered to include collections having a polycystode
rm (epithelium). Quadrispora includes species with assymetrical spores
that adhere in tetrads after release from the basidium. H. oblongispo
rus is recombined into the new genus, and Q. musispora is described as
new. The relationships of Quadrispora to other fungi are not known. F
inally, Timgrovea is proposed to accommodate species with reticulate s
pores, T. reticulatus, T. macrosporus, T. subtropicus, and T. ferrugin
eus from Australia, and T. kwangiensis from China. The relationships o
f Timgrovea probably occur outside the Cortinariaceae. A possible rela
tionship of Timgrovea to the Boletaceae is discussed.