Endogonales
Overview
The Endogonales contains a single family, the Endogonaceae, which did not appear in a taxonomic scheme of the Zygomycetes until Fitzpatrick (1930) treated the group. Fitzpatrick followed Thaxter (1922) who monographed the Endogonaceae, and included sporocarpic taxa from the genera Endogone, Glaziella, Sclerocystis, and Sphaerocreas. Sphaerocreas was not included in the family in other taxonomic treatments (Hesseltine, 1955; Benjamin, 1959; Zycha et al., 1969). Hesseltine and Ellis (1973) included Endogone, Glaziella, and Sclerocystis, as certain members of the Endogonaceae, but other fungi were thought to be potential members of the family, including some species of Mortierella (those spp. producing their zygospores in a mycelial covering resembling a sporocarp). Other genera mentioned were Azygozygum (Chesters, 1933) which forms both zygospores and chlamydospores but not sporangiola (this taxon is included in Mortierella (Mortierellaceae [Mortierellales] here) and Massartia, an organism that produces only a teleomorphic state (smooth-walled zygospores formed on tong-like suspensors). Massartia (de Wildeman, 1897) was treated as a doubtful or excluded member of the Mucorales by Hesseltine (1955).
A true renaissance in the taxonomy of the Endogonaceae was started with the publication of “The Endogonaceae of the Pacific Northwest” (Gerdemann and Trappe, 1974) in which seven genera were recognized. These taxa either produced sporocarps that contained only zygospores (Endogone—11 spp.), sporangiola (Modicella—2 spp.), or “chlamydospores” [Sclerocystis—4 spp.; Glomus (in part)—18 spp.; Glaziella—1 sp.], or the reproductive structures are not in sporocarps but are formed freely in the soil as “chlamydospores” [Glomus (in part)—18 spp.) or “azygospores” (Gigaspora—5 spp.; Acaulospora—2 spp.). These spores were called “azygospores” because of a superficial similarity to the zygospores produced by Endogone spp. (Gerdemann and Trappe, 1974).
Three additional genera were added to the Endogonaceae after Gerdemann and Trappe’s (1974) monograph: Entrophospora (Ames and Schneider, 1979), Complexipes (Walker, 1979) (both genera were monotypic when described), and Scutellospora (Walker and Sanders, 1986), a segregate from Gigaspora that included 17 spp. when proposed.
Yao et al. (1996) continued to include most of the genera listed above in the Endogonales except Azygozygum, Complexipes, Glaziella, Massartia, Modicella, and Sphaerocreas but they added Sclerogone and Youngiomyces. Earlier, Morton and Benny (1990) proposed the Glomales for the fungi then in the Endogonales that formed Endomycorrhizae; several genera (Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis, Scutellospora) were then transferred to the Glomales. Recently, Schüssler et al., 2001) created a new phylum (Glomeromycota) for the Glomales (their Glomerales) and then proposed several new orders and a phylogeny that also contained Geosiphon piriforme (Geosiphonaceae, Geosiphonales). The treatment of the Glomeromycota proposed above is being followed here and, therefore, the Zygomycota will not continue to include these fungi.
Several species of Endogone (E. aggregata, E. flammicorona, E. lactiflua, E. tuberosa) and Sclerogone eucalypti are known that form ectomycorrhizae (Fassi et al., 1969; Warcup, 1990). Other species of Endogone, including E. pisiformis, did not produce ectomycorrhizae; the fungal hyphae did not penetrate the root but grew along it surface instead (Berch and Castellano, 1986).
One species, Endogone pisiformis (Dalpé, has been studied extensively in culture. Zygospore germination of E. pisiformis was reported over two decades ago (Berch and Fortin, 1983b). This resulted in the successful culture of this fungus in pure culture (Berch and Fortin, 1983a; Dalpé, 1990). Dalpé (1990) was able to grow cultures of E. pisiformis on various media but vitality was maintained only after the inclusion of thiamine. Endogone pisiformis was induced to produce sporocarps and zygospores on a culture medium containing the minerals in peat-vermiculite and a simple sugar (Berch and Castellano, 1986); sporangia were never present. There was a temperature gradient in the test tubes used from 18 C where mycelium was produced in the culture medium to 23 C on the walls where the sporocarps formed (Berch and Castellano, 1986).
All of the taxa (Endogone, Peridiospora, Sclerogone, Youngiomyces) currently included in the Endogonales produce zygospores with apposed suspensors in sporocarps (Thaxter, 1922; Gerdemann and Trappe, 1974; Warcup, 1990; Yao et al., 1995, 1996; Wu and Lin, 1997). At the present time no other reproductive structures have been described. There is one report in the literature (Kanouse, 1936) of sporangia being produced but Berch and Castellano (1986) believe that the report was based on a contaminated specimen.
Classification
Endogonales F. Moreau ex R.K. Benjamin, 1979 (in B. Kendrick, The Whole Fungus, p. 599) emend Morton & Benny, 1990 (Mycotaxon 37:473).
= Endogonales F. Moreau, 1953 (Encycl. Mycol. 23:1231; nomen nudum, without a Latin diagnosis, Art. 36.1 of the ICBN (Greuter et al., 2000).
Hyphae coenocytic but with occasional multiperforate septa. Reproduction by zygospores with apposed suspensors enclosed in epi- or hypogeous, uni- or multispored sporocarps. Saprobic, ectomycorrhizal, or hyphae may grow along plant root but does not penetrate host cells.
Type Family: Endogonaceae
Endogonaceae Paoletti, 1889 (in P.A. Saccardo, Syll. Fung. 8:905) emend Morton & Benny, 1990 (Mycotaxon 37:473).
With the characteristics of the order.
Type Genus: Endogone Link: Fr.
Updated Jan 15, 2005