Delimitation of Hymenogaster Sensu Stricto and Four New Segregate Genera

Since Vittadini first described Hymenogaster in 1831, a heterogeneous assemblage of truffle-like Basidiomycetes has been assigned to the genus. As a consequence, the boundaries of Hymenogaster became inflated even beyond Vittadini's original broad concept, and the genus came to represent more than one phylogenetic line. This paper clarifies the generic limits of Hymenogaster and challenges a prevailing notion that Hymenogaster represents the hypogeous member of a phylogenetic line linked through Thaxterogaster to Cortinarius.On the basis of both macromorphological and micromorphological characters of basidiomes, Hymenogaster sensu stricto is redefined. Selected species are allocated to four new genera: Cortinomyces, Descomyces, Quadrispora, and Timgrovea. A key to these genera is provided.Four of the eight original Vittadini species are excluded from Hymenogaster: H. rufus (type lost), H. citrinus (to Gautieria), H. luteus (to Hysterogaster), and H. niveus (to Cortinomyces). The remaining four species have large, thick-walled, broad ellipsoid to fusiform spores bearing a large, cupped hilar appendix and are designated as the core of Hymenogaster since they include the type species H. bulliardi. Also included with the type are H. olivaceus, H. lycoperdineus and H. griseus. The relationships of these Hymenogaster 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 Cortinomyces by virtue of its smaller, warty spores.Cortinomyces is largely distinguished from Hymenogaster by having cortinarioid spores. Numerous other characters, such as peridial pigments and structure, suggest that Cortinomyces fits into a phylogenetic series with Thaxterogaster and Cortinarius. Hymenogaster cribbiae, H. effodiendus, H. luteus (non Vittadini), H. niveus, H. purpureus, H. violaceus, and H. viscidus are recombined to Cortinomyces.Descomyces has distinctive spore morphology (e.g., a smooth rostrum and ornamentation embedded in the perisporium) and peridium structure (e.g., two layered and with swollen cells). This peculiar combination of peridial and spore characteristics also occurs in Setchelliogaster and in Descolea. It is proposed that Descomyces (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 hymenium). Further supporting evidence of this relationship is obtained from examination of mycorrhizae and axenic cultures of these fungi. Species 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 polycystoderm (epithelium).Quadrispora includes species with assymetrical spores that adhere in tetrads after release from the basidium. H. oblongisporus is recombined into the new genus, and Q. musispora is described as new. The relationships of Quadrispora to other fungi are not known.Finally, Timgrovea is proposed to accommodate species with reticulate spores, T. reticulatus, T. macrosporus, T. subtropicus, and T. ferrugineus from Australia, and T. kwangiensis from China. The relationships of Timgrovea probably occur outside the Cortinariaceae. A possible relationship of Timgrovea to the Boletaceae is discussed.