Synonym and Classification Data for Emmonsia spp.
This genus is a mould that lacks a known sexual state and thus belongs to the Fungi Imperfecti. See also the detailed description page for this genus.
Notes on this Genus
The designation of “dimorphic” is sometimes also applied to this genus as its members may produce a special structure called an “adiaspore” at 37 or 40°C. Adiaspores are thick-walled, enlarged conidia that may be uni- or multinucleate. This dimorphism is not a true dimorphism (i.e., it is not the same as for Histoplasma capsulatum) as there is no mould-to-yeast conversion at 37°C. The only thing that happens is that a special morphological form is produced at 37°C both in vivo and in vitro. As a comparison, consider Candida. It is a yeast, but on occasions it is called “dimorphic” due to its ability to produce both yeast cells and hyphae. Another example would be the fungi that cause chromoblastomycosis where those phaeoid moulds are sometimes called dimorphic due to their in vivo production of “sclerotic bodies.”
Species in this genus
- Emmonsia crescens (obsolete)
- Emmonsia parva (dimorphic)
Notes: The sexual stage for this species was described by Lynne Sigler (J. Med. Vet. Mycol. 34:303-314; 1996) who placed it in the genus Ajellomyces as A. crescens. The conidia of Chrysosporium parvum are morphologically like those of Blastomyces dermatitidis and the microconidia of Histoplasma capsulatum. They are also morphologically very similar to Paracoccidioides brasiliensis. Depending upon how you define Chrysosporium, it could belong either to the genus Chrysosporium or Emmonsia.
The genus Chrysosporium is based upon the development of lateral thallic conidia and the presence of arthroconidia, which are also thallic conidia. The genus Chrysosporium is thus based upon morphology. The genus Emmonsia was originally proposed to describe adioconidia in tissue of rodents and a mould that formed lateral one-celled conidia in culture. The genus Emmonsia is thus an ecologically based genus rather than a morphologically based genus. That is, its definition reflects a transition from one morphological form to another based upon incubation temperature. This same concept can be used for the dimorphic fungi that exhibit ecologically based adaptive changes in morphology caused by temperature of incubation. This would explain why Blastomyces and Histoplasma have not been accepted as species of Chrysosporium, or Coccidioides immitis is not accepted as a species of Malbranchea. Interestingly, Sporothrix schenckii is also an ecologically based species concept, but the fungus is classified in the genus Sporothrix based upon its conidia and the species is based upon temperature-related form transitions.
We thus believe that the best name for Chrysosporium parvum is Emmonsia parva. From an ecological species concept for the fungus, Emmonsia parva clearly reflects the ability of the fungus to consistently produce two different forms based upon temperature. This parallels the other species in the teleomorphic genus Ajellomyces. The argument in favor of Emmonsia is not really morphologically based, but ecologically and phylogenetically based. A major goal of any classification system is to reflect phylogenetic relationships.
In reality can these anamorphs (Blastomyces, Histoplasma, Emmonsia, and Paracoccidioides) morphologically be placed in the genus Chrysosporium? Absolutely! To maintain nomenclatural stability we should, however, continue to use the names Blastomyces, Histoplasma, Emmonsia, and Paracoccidioides. By extension, one would also predict that the as-yet-undiscovered sexual stage for Paracoccidioides will be in the genus Ajellomyces.
This species is a synonym of Chrysosporium parvum var. parvum
This species is a synonym of the obsolete species E. crescens
Chrysosporium parvum is a synonym of this species.
Chrysosporium parvum var. parvum is a synonym of this species.
- Emmonsia parva var. crescens (dimorphic)
- Emmonsia parva var. parva (dimorphic)
- Emmonsia pasteuriana