The two genera, Radiomyces and Hesseltinella, originally included in the Radiomycetaceae by Hesseltine and Ellis (Ellis and Hesseltine, 1974), earlier had been placed in the Thamnidiaceae sensu Hesseltine (1955). However, species of these genera differ from all Thamnidiaceae (Benny, 1973; Benny and Benjamin, 1975, 1976) in their distinctive zygospores and in characteristics of their sporangiola-bearing branches.

In Radiomycetaceae sensu Hesseltine and Ellis (Ellis and Hesseltine, 1974), the fertile vesicle, bearing one or many sporangiola, is subtended by a uniseptate stalk, which itself arises from an intercalary or terminal sporophoric vesicle. Zygospores, presently known only for Radiomyces spp., are smooth, have a thin, transparent zygosporangial wall, and are enveloped by a complex of branched, attenuate appendages arising from the suspensors.

The development of sporangiola and sporangiola appendages was demonstrated in Hesseltinella vesiculosa Upadhyay, R. embreei_ R.K. Benj., and R. spectabilis Embree (Benny and Samson, 1989). It was also shown that the morphology of the appendages of H. vesiculosa could change in a moist environment when the water was saturated with calcium oxalate, the chemical component of these ornaments (Benny and Khan, 1988). An additional species of Radiomyces, R. mexicana Benny & R.K. Benjamin, was added in the monograph of Radiomycetaceae (Benny and Benjamin, 1991).

A data set consisting of six taxa from the Mortierellales and 75 spp. containing at least one species all of the genera in culture of the Mucorales (tef-1a, 18S rDNA, 28S rDNA, morphology) demonstrated that Radiomyces is in a three-genus clade (including Apophysomyces and Saksenaea) with 85% bootstrap percentage (BP) according to O’Donnell et al. (2001); the Radiomyces clade had 83% bootstrap support (BP). A data set (act, tef-1a, 18S rRNA, 28S rRNA) containing selected species of 50 genera of the Mucorales analyzed by neighbor-joining (92% BP) and strict concensus (69% BP) for the Radiomyces clade (Voigt and Olsson, 2008). Radiomyces is being treated in its own family here because its sister taxa (Apophysomyces, Saksenaea) are in a clade with 100% BP (O’Donnell et al, 2001; Voigt and Olsson, 2008). Radiomyces is being teated as the only genus in the Radiomycetaceae here based on these phylogenetic studies (O’Donnell et al., 2001; Voigt and Olsson, 2008).

Cannon and Kirk (2007) and Kirk et al. (2008) include three genera in the Radiomycetaceae. Two websites, Encyclopedia of Life ( and Species 2000 Catalogue of Life 2009 Annual Checklist ( also list three genera (Apophysomyces, Radiomyces, Saksenaea) in the family. Radiomycetaceae (Radiomyces) have been isolated from dung (Benny and Benjamin, 1991). There currently are no economic uses known for species of Radiomyces.

Radiomycetaceae Hesseltine & Ellis, 1974 (In Ellis and Hesseltine, Mycologia 66: 91).

= Radiomycetaceae Hesseltine & Ellis, 1973 [In Ainsworth, Sparrow, and Sussman. The Fungi, Vol. 4B, p. 202 [nomen nudum, without a Latin diagnosis; Art. 36.1 of the ICBN (McNeill et al., 2006)].

Sporophores arising from aerial hyphae directly or subtended by rhizoids, producing terminal vesicles bearing uniseptate stalks terminated by fertile vesicles, which bear one or several pedicellate sporangiola. Sporangiola uni- or multispored, acolumellate; wall bearing capitate appendages. Suspensors opposed, nearly equal, bearing irregularly branched, sinuous, acuminate appendages that invest the zygospore. Zygospores hyaline or pigmented; zygosporangial wall thin and smooth, transparent.

Type and only genus: Radiomyces

Synopsis of the Genus

RADIOMYCES Embree, 1959 (Amer. J. Bot. 46: 25); 3 spp. (Embree, 1959 — ILLUS.; Benjamin, 1960 — ILLUS.; Benny and Khan, 1988; Benny and Samson, 1989 — illus.; Benny and Benjamin, 1991 — revision).
= Radiomycopsis Pidopl. & Mil’ko, 1971 (Atlas of Mucoralean Fungi, p. 95).

Genera Not Accepted Here but Included in the Radiomycetaceae by Some Authors

[Apophysomyces — see Saksenaeaceae (Mucorales)].

[Hesseltinella — see Synopsis of the Genera with Unknown Affinities (Mucorales)].

[Saksenaea — see Saksenaeaceae (Mucorales)].


Benjamin, R.K. 1960. Two new members of the Mucorales. Aliso 4:523-530.

Benny, G.L. 1973. A taxonomic revision of the Thamnidiaceae (Mucorales. Claremon Graduate School, Claremont, California, U.S.A. 252 p.

Benny, G.L., and R. K. Benjamin. 1975. Observations on Thamnidiaceae (Mucorales). New taxa, new combinations, and notes on selected species. Aliso 8: 301-351.

Benny, G.L., and R.K. Benjamin. 1976. Observations on Thamnidiaceae (Mucorales). II. Chaetocladium, Cokeromyces, Mycotypha, and Phascolomyces. Aliso 8: 391-424.

Benny, G.L., and R.K. Benjamin. 1991 [1992]. The Radiomycetaceae (Mycorales; Zygomycetes). III. A new species of Radiomyces, and cladistic analysis and taxonomy of the family; with a discussion of the evolutionary ordinal relationships in Zygomycotina. Mycologia 83: 713-735.

Benny, G.L., and S.R. Khan. 1988. The Radiomycetaceae (Mucorales; Zygomycetes). Calcium oxalate crystals on the sporangiolar wall and aerial hyphae. Scanning Microscopy 2(2):1199-1206.

Benny, G.L., and R.A. Samson. 1989. The Radiomycetaceae (Mucorales, Zygomycetes). II. Ultrastructural morphology of the mature zygospore and comparative morphology of the sporangiola and sporangiolar appendages. Memiors of the New York Botanical Garden 49:11-19.

Cannon, P.F., and P.M. Kirk. 2007. Fungal families of the World. Wallingford, United Kingdom, CAB International. 456 p.

Ellis, J.J., and C.W. Hesseltine. 1974. Two new families of Mucorales. Mycologia 66:87-95.

Embree, R.W. 1959. Radiomyces, a new genus in the Mucorales. American Journal of Botany 46:25-30.

Hesseltine, C.W. 1955. Genera of Mucorales with notes on their synonymy. Mycologia 47:344-363.

Kirk, P.M., P.F. Cannon, D.W. Minter, and J.A. Stalpers. 2008. Ainsworth & Bisby’s Dictionary of the Fungi. 10th Ed. Wallingford, United Kingdom, CAB International. 771 p.

McNeill, J., F.R. Barrie, H.M. Burdet, V. Demoulin, D.L. Hawksworth, K. Marhold, D.H. Nicolson, J. Prado, P.C. Silva, J.E. Skog, J.H. Wiersema and N.J. Turland. [eds.]. 2006. International Code of Botanical Nomenclature (Vienna Code). [Regnum Vegetabile Vol. 126]. A.R.G. Gantner Verlag KG, Ruggell, Liechtenstein. 568 p.

O’Donnell, K., F.M. Lutzoni, T.J. Ward, and G.L. Benny. 2001. Evolutionary relationships among mucoralean fungi (Zygomycota): Evidence for family polyphyly on a large scale. Mycologia 93:286-296.

Voigt, K. and I. Olsson. 2008. Molecular phylogenetic and scanning electron microscopical analysis places the Choanephoraceae and the Gilbertellaceae in a monophyletic group within the Mucorales (Zygomycetes, Fungi). Acta Biologica Hungarica 59:365-383.

Updated Jun 06, 2010