Abstract
Although frequently found on mounds of the grass-cutting termite genus Trinervitermes, virtually nothing is known about the natural history of the fungal genus Podaxis (Agaricaceae) nor why it associates with termite mounds. More than 40 species of this secotioid genus have been described since Linnaeus characterised the first species in 1771. However, taxonomic confusion arose when most of these species were reduced to synonymy with Podaxis pistillaris in 1933. Although a few more species have since been described, the vast majority of specimens worldwide are still treated as P. pistillaris. Using 45 fresh and herbarium specimens from Southern Africa, four from North America and one each from Ethiopia, and Kenya, we constructed the first comprehensive phylogeny of the genus. Four of the genotyped specimens were more than 100 y old. With the exception of the type specimen of Podaxis rugospora, all herbarium specimens were labelled as P. pistillaris or Podaxis sp. However, our data shows that the genus contains at least five well-supported clades with significant inter-clade differences in spore length, width and wall thickness, and fruiting body length, supporting that clades likely represent distinct Podaxis species. Certain clades consistently associate with termites while others appear entirely free-living.
Highlights
Little is known about the biology of the secotioid fungal genus Podaxis (Family: Agaricaceae) or the nature of its apparent relationship with termites
In sampling at Maropeng, South Africa, we collected one maturing fruiting body, which revealed that the immature spores are white before changing to green and black as they mature (Fig 1E)
We successfully extracted high-enough quantity and quality DNA for PCR and phylogenetic analyses from 42 of the collection of specimens, including four herbarium specimens that were more than 100 y old (Table 1)
Summary
Little is known about the biology of the secotioid fungal genus Podaxis (Family: Agaricaceae) or the nature of its apparent relationship with termites. Distributed between À40 and þ40 latitude (Morse 1933), the genus has a long history of being reported in association with the grass-harvesting termite genera Trinervitermes (Family: Termitidae, subfamily: Nasutitermitinae) in Africa and Nasutitermes (Family: Termitidae, subfamily: Nasutitermitinae) in Australia (Massee 1890; Priest & Lenz 1999). Bosc (1792) described a third species (Lycoperdon axatum) from Senegal that was renamed Podaxis senegalensis (Desvaux 1809) and designated as the type species of the new genus Podaxis. Morse (1933), who focused predominantly on North American (mainly Californian) specimens, reduced the thirty-two described species to synonymy as a single, polymorphic species: Podaxis pistillaris (Morse 1933; Bottomley 1948); including the type species of the genus, P. senegalensis, as synonym of P. pistillaris. Without considering all the older taxa, some authors during this period described new species that they distinguished from P. pistillaris
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