Type species: Blackwellomyces cardinalis (G.H. Sung & Spatafora) Spatafora & Luangsa-ard 2017. Basionym: Cordyceps cardinalis Sung and Spatafora 2004.

Etymology: This genus is named for Meredith Blackwell and honours her invaluable contributions to our knowledge of insect-associated fungi.

Diagnosis: Blackwellomyces is the least inclusive genus level clade that originally includes the species B. cardinalis and B. pseudomilitaris. Blackwellomyces is diagnosed by the unique characters of the ascospore, which have irregularly spaced septa and do not disarticulate into part-spores at maturity.

Description: Sexual morph: Stromata solitary or multiple, simple or branched. Stipe fleshy, orange to red, cylindrical to enlarging apically, 4–50 × 0.5–3.0 mm. Fertile area terminal, cylindrical, fusiform to clavate to irregularly shaped, 2–9 × 1–4 mm. Perithecia crowded, loosely embedded, ordinal in orientation, elliptical to fusiform to obclavate. Asci 8-spored, hyaline, cylindrical, possessing a prominent apex. Ascospores smooth, filiform, hyaline, irregularly multiseptate, not fragmenting into part-spores. Asexual morph: Cultures moderately fast growing in PDA and may turn the media red. Aerial mycelium is whitish to whitish yellow and the reverse side of cultures is red or cream. Conidiogenous cells phialides, solitary or in whorls of 2 or 3, swollen at the base or slightly flask-shaped, wider near the base and tapering at the apex. Conidia hyaline, aseptate, ellipsoidal to elliptical, in some species produced in sympodially imbricate chains. Asexual morphs have been described as similar to species in Clonostachys, Hirsutella, Isaria, and Mariannaea.

Hosts: On larva of Lepidoptera.

Distribution: Southeastern USA, eastern China, Japan, Korea, and Thailand.

Commentary: The species placed here are supported as a distinct clade and separate from other genera of Cordycipitaceae based on the placement of their type species. We describe these taxa as Blackwellomyces on the basis of their phylogenetic novelty and irregularly septate ascospores that do not disarticulate into part-spores. This contrasts with other members of the family in which septation and disarticulation is common.