Classification. Up until recently the majority of hypocrealean arthropod pathogenic (AP) fungi were classified in the genus Cordyceps in the family Clavicipitaceae (Spatafora & Blackwell 1993). This classification was based on the characters of cylindrical asci with thickened ascus apices and filiform ascospores that often disarticulate into part-spores. Cordyceps was characterized and distinguished from other genera of the family by its production of superficial to completely immersed perithecia on stipitate and often clavate to capitate stromata and its ecology as a pathogen of arthropods and of truffles in the genus Elaphomyces (Kobayasi 1941; Mains 1957, 1958). Recent phylogenetic studies with 5 to 7 genes rejected the monophyly of both Cordyceps and Clavicipitaceae, however, and supported three clavicipitaceous clades that have been classified as three monophyletic families: Clavicipitaceae s.s., Cordycipitaceae and Ophiocordycipitaceae (Sung et al 2007a, 2007b; Spatafora et al 2007). Cordyceps sensu lato was divided into four genera (e.g., Cordyceps s. s., Elaphocordyceps, Metacordyceps and Ophiocordyceps) based on this phylogeny (Sung et al 2007b). The characters most consistent with the phylogeny were texture, pigmentation and morphology of stromata and not presentation of perithecia and ascospore morphology as traditionally emphasized in Cordyceps taxonomy. The current phylogenetic classification of hypocrealean AP fungi is as follows:
Clavicipitaceae: Conoideocrella, Hypocrella, Metacordyceps, Moelleriella, Orbiocrella, Regiocrella, Samuelsia, Shimizuomyces, Villosiclava
Cordycipitaceae: Ascopolyporus, Cordyceps, Hyperdermium, Torrubiella
Ophiocordycipitaceae: Cordyceps s.l., Elaphocordyceps, Ophiocordyceps
Phylogenetic tree. This phylogenetic tree is based on a RAxML analysis of a multigene dataset of five gene regions including SSU rDNA, LSU rDNA, TEF1, RPB1 and RPB2. The color on the branches represent the ancestral host reconstruction for host affiliation. Classification and nomenclature follows that of Sung et al 2007, Studies in Mycology. Click on the tree to view a larger image.
Genera. General characteristics of the major genera of species formally classified in Cordyceps s.l. are as follows but see Sung et al 2007 for complete descriptions:
Cordyceps s.s. consists almost entirely of pallid to brightly colored species that produce soft fleshy stromata (e.g., C. militaris). The majority of species attack larvae and pupae of Lepidoptera and Coleoptera in leaf litter, moss or upper soil layers. Numerous species that produce highly reduced stromata, loosely organized hyphae, or a subiculum on the host also occur in this genus (e.g. C. tuberculata), some of which were previously classified in Torrubiella (e.g., T. confragosa).
Elaphocordyceps includes all species that parasitize Elaphomyces and closely related species that attack nymphs of cicadas. The morphology of the Elaphomyces parasites and the cicada pathogens are remarkably similar and attest to the recent history of inter-kingdom host-jumps in a common subterranean environment (Nikoh & Fukatsu 2000). The exception to this genus is E. subsessilis, which macroscopically and ecologically is distinct from the rest of the species, but is well supported as being a member of the genus based on molecular data and micromorphology.
Metacordyceps includes only a limited number of described species, of which all but one is known from East Asia. The stromatal color of fresh specimens ranges from white (e.g., M. yongmunensis) to lilac, purple or green, and the darker pigments are almost black in dried specimens (e.g., M. taii). The texture of the stromata is fibrous and not fleshy like Cordyceps s. s., and the hosts are almost always buried in soil.
Ophiocordyceps is the largest genus of arthropod pathogenic fungi. Many species are darkly pigmented and occur on immature stages of hosts buried in soil (e.g., O. sinensis) or in decaying wood (O. variabilis). Notable exceptions exist for both of these traits among species that attack adult stages of hosts, however. For example, O. unilateralis is common on adult ants and occurs on the under sides of leaves, and O. sphecocephala is common on adult wasps and is found in leaf litter. Stromatal morphology is diverse, ranging from filiform and wiry to clavate and fibrous, according to species, and many species produce their perithecia in nonterminal regions of the stroma, either distinctly superficial, or in broad irregular patches, or in lateral pads.
(Note: Approximately, 160 residual species of Cordyceps sensu Kobayasi and Mains could not be accommodated in the current classification due to insufficient data and are classified as residual species of Cordyceps s.l. Also, preliminary results confirm that Torrubiella is not monophyletic with species distributed in Clavicipitaceae, Cordycipitaceae and Ophiocordycipitaceae.)