Leohumicola, a new genus of heat-resistant hyphomycetes

The new anamorph genus Leohumicola (hyphomycetes) is described for four species, including three new species isolated after heat treatment of soils collected in Canada. The species produce slow-growing agar colonies that eventually produce lateral or terminal aleurioconidia, with a dark brown terminal cell, and the remains of a paler basal cell that fractures during secession. The genus is compared with Humicola, Trichocladium, Thermomyces, Complexipes and some other morphologically similar genera. Nuclear ribosomal small subunit (SSU) ribosomal DNA sequences demonstrate that Leohumicola is a monophyletic group in the Leotiomycetes, distinct from Humicola and Trichocladium (Sordariales), and Thermomyces (Eurotiales). Internal transcribed spacer sequences (ITS) support our recognition of four species of Leohumicola, each with distinct colony and micromorphological characters. The existence of additional species is probable based on our own ITS sequences and some retrieved from GenBank. The type species L. verrucosa, was recovered from a variety of soil types across Canada, and has sympodially proliferating conidiogenous cells that produce conidia with verrucose terminal cells that measure 4-5.5 x 4-5.5 mu m. The SSU of some strains of this species have five long Group I introns that extend the length to more than 3700 nt. Leohumicola lenta produces very slowly growing colonies on agar media and larger conidia than L. verrucosa, and L. terminalis produces only terminal conidia. The latter two species are represented by single strains. The fourth species, L. minima is based on Trichocladium minimum, originally isolated from volcanic ash soil from Chile. Internal transcribed specer (ITS) sequences suggest that Humicola is a synonym of Trichocladium, a finding that may require conservation of Humicola. Dichotomous keys are provided to the accepted species of Leohumicola, and to morphologically similar aleurioconidial genera.