Dimargaritales
Overview
Two of the species, Dimargaris cristalligena van Tiegh. and Dispira cornuta van Tiegh., included in the Dimargaritaceae by Benjamin (1959), were known before he described several additional taxa in the family. Only D. cornuta appeared in the literature (Benjamin, 1959) after van Tieghem (1875) had described the fungus, and D. cristalligena was not reported between 1875 and 1959, when the fungus was redescribed by Benjamin (1959).
After Benjamin (1959), all students of the Zygomycetes (Zycha et al., 1969; Hesseltine and Ellis, 1973; Benjamin, 1979) recognized the Dimargaritaceae, which contained the following genera: Dimargaris, Dispira, Spinalia, and Tieghemiomyces. Spinalia has been reported once (Wrzosek and Gajowniczek, 1998) since originally described by Vuillemin (1904). It is an unusual member of the Dimargaritaceae because the merosporangia are not formed on sporiferous branchlets but they arise directly from the fertile vesicle.
The majority of the species in Dimargaris, Dispira, and Tieghemiomyces have been grown in axenic culture with a suitable host. Most of these taxa are haustorial mucoralean parasites and can be grown successfully in the laboratory on Cokeromyces recurvatus Poitras (Spinalia radians has not been cultured), except Dispira simplex (Benjamin, 1959, 1961) and D. implicata Misra & Lata (Misra and Lata, 1979) which normally parasitize Ascomycetes (Chaetomium spp.). Also, the majority of the Dimargaritaceae are coprophilous, but some spp. have been isolated from the sap of a birch stump (S. radians—Vuillemin, 1904) or more commonly from soil (Dimargaris simplex B.S. Mehrotra & Baijal and D. arida (Benjamin, 1965).
The majority of the species of the Dimargaritaceae are dry-spored at maturity, including Dimargaris xerosporica (Mehrotra and Baijal) R.K. Benjamin and D. arida (Benjamin, 1965); the remaining Dimargaris spp. release their spores in a droplet of fluid at maturity (Benjamin, 1965). Two species of Dimargaris, D. bacillispora Benjamin (1959) and D. oblongispora Mehrotra & Baijal, are unusual in their mode of merosporangial ontogeny because both spores are formed simultaneously, i.e., the merosporangium reaches its mature size before the spores are cleaved out (Benjamin, 1966). In the remaining taxa of the Dimargaritaceae (Benjamin, 1959, 1961, 1963, 1965, Misra and Lata, 1979) the merosporangia are formed successively, i.e., the younger spore buds off of the apex of the older, subtending propagule (Benjamin, 1966).
Septal plugs in Dimargaris cristalligena have a globose, upper and a broadly acute, rounded, lower protuberance (Benjamin, 1959; Benny, 1972), whereas both structures are globose in the remaining species of the Dimargaritaceae. The structure of the cell walls and septa is similar in all species. The cell wall consists of two layers, the outer of which is relatively thin and continuous, whereas the inner one is thicker, discontinuous [interupted at the septum, with the end walls of each cell making up one-half of the cross wall (Benjamin, 1959)] and produces the septum which contains a lenticular cavity and a septal plug with characteristic projections (see above). The septum and inner cell wall layer are continuous and they are composed of chitin and hemicellulose, with the addition of hyaluronic acid in the septum. The outer cell wall layer and septal plug contain soluble, bound, acid-fast lipids, and lipofuscin pigments, and in addition unsaturated lipids are also present in the outer layer of the cell wall (Benny, 1972). Septal ultrastructure has been examined in Dimargaris spp. (Saikawa, 1977), Dispira cornuta (Saikawa, 1977), and Tieghemiomyces californicus (Brain et al., 1982). All of these fungi produce a similar septum and plug when observed with TEM and this data correlates well with data obtained with LM.
Dimargaris verticellata Benjamin, a mucoralean parasite, has a broad host range within the Mucorales, but none of the Ascomycetes or Basidiomycetes served has a host under test conditions (Mandelbrot and Erb, 1972). Dispira simplex Benjamin can parasitize a number of Chaetomium spp. but the host range can vary by manipulating the ratio of glucose to yeast extract in the culture medium; some mucoralean fungi and Monascus purpurescens Went. also can be parasitized, but the number of fungi serving as host can be varied by manipulating the ratio of nutrients mentioned above (Brunk and Barrnett, 1966). Many spp. of the Dimargaritaceae can be grown in pure culture without a host (Benjamin, 1959) but growth and sporulation is sparse. Most Dimargaritales will grow without a host on YGCH medium (see under Kickxellales) which uses glycerol as a carbon source instead of glucose. Barnett and his students devised methods of producing good growth and sporulation by manipulating nutrients and their concentration in the medium (Barnett, 1970; Binder and Pearce, 1976).
Classification
DIMARGARITALES R. K. Benjamin, 1979 (In Kendrick, The Whole Fungus, p. 607).
Haustorial parasites of other fungi. Mycelium branched, septate, producing simple or branched, septate sporophores. Septa with single lenticular cavities, containing plugs bearing polar protuberances; plugs dissolving in 2-3% KOH. Asexual reproduction by sporangiospores produced in two-spored merosporangia arising directly from a terminal vesicle, or specialized sporiferous branchlets arising from a vesicle or from the noninflated apex of the sporophore. Sporiferous branchlets simple or branched. Sexual reproduction by hyaline, more or less globose zygospores having a smooth or ornamentated wall; zygosporangial wall thin, smooth; sexual hyphae undifferentiated, similar to vegetative hyphae.
Type family: Dimargaritaceae R. K. Benjamin.
One family is recognized.
Dimargaritaceae R. K. Benjamin, 1959 (Aliso 4:364)
(Benjamin, 1959—KEY TO GENERA, 1966, 1979; Zycha et al., 1969—key to genera).
With the characteristics of the order.
Type genus: Dimargaris van Tieghem.
Updated Jan 15, 2005