Zygosporangia occur in loose aggregates or singly in the soil.
AGGREGATES ovoid; 160-270 x 250-500 µm; composed of 2-4 loosely and randomly positioned zygosporangia enveloped individually by hyphal mantle.
Mantle (4.9-)16.0(-32.5) µm thick; consisting of interwoven, sinuous, hyaline to orange white (5A2) hyphae; (2.5-)7.9(-10.0) µm diam; mantle hyphae adherent to zygosporangia more compactly interwoven and darker coloured than those positioned in the outer region of the mantle; hyphae of the outer mantle layer branched and interwoven with those of neighboring zygosporangia.
ZYGOSPORANGIA deep orange (6A8); globose to subglobose; (100-)139(-180) µm diam; sometimes ovoid or broadly ellipsoidal; 120-150 x 140-180 µm; with a circular pore, 7.5-12.5 µm diam, at the junction of the larger of the two gametangia.
Zygosporangial wall (zlw) consists of a single layer, deep orange (6A8), (0.8-)1.4(-2.0) µm thick, ornamented with evenly distributed conical warts, 0.4-0.7 µm wide at the base, 0.4-0.7 µm high.
Zygospore wall (zew) single, smooth, hyaline, (1.0-)2.0(-2.9) µm thick, usually tightly adherent to the zygosporangial wall.
Gametangial wall smooth, 1.8-3.9 µm thick at the zygosporangial base; wall of the larger gametangium continuous with the zygosporangial wall.
Gametangia usually covered by hyphal mantle of zygosporangia.
Zygospore contents of hyaline lipid globules.
Zygosporangia, zygospores, gametangia, and hyphal mantle not reacting in Melzer’s reagent.
DISTRIBUTION. In Poland, E. aurantiaca has been found in rhizosphere soils of P. sylvestris growing in the Kampinos National Park (52o18’N, 20o46’E), the Hel Peninsula (54o36'-54o47'N, 18o25'-18o48'E), Zelistrzewo (54o57'N, 18o13'E; the Pomerania province), Ploty (53o56'N, 14o56'E; the Western Pomerania province), and Bydgoszcz (53o7’N, 18o1’E; Blaszkowski 1997; pers. observ.). No report of the presence of this fungus in other regions of the world exists.
NOTES. Endogone aurantiaca is distinctive due to the formation of zygosporangia in loose aggregates or singly in the soil and especially by its ornamented zygosporangial wall. The characteristic feature of this species also is the lack of a peridium.
Species of the genus Endogone forming zygosporangia resembling in colour and size those of E. aurantiaca are E. alba (Petch) Gerd. & Trappe, E. flammicorona Trappe & Gerd., and E. lactiflua Berk. & Broome (Gerdemann and Trappe 1974; Pegler et al. 1993; Yao et al. 1992). However, these species produce compact sporocarps surrounded by a peridium (vs. loose aggregates without a peridium or single zygosporangia in E. aurantiaca). The zygosporangia of E. aurantiaca, E. flammicorona, and E. lactiflua are enclosed by a hyphal mantle that is absent in E. alba. The hyphal mantle of E. aurantiaca is formed by interwoven sinuous hyphae. Endogone flammicorona also has a mantle with a spiral, sinuous pattern when observed in a plan view (Gerdemann and Trappe 1974). However, in a cross-sectional view, this mantle resembles a crown or „tongues of flame” produced by hyphal ridges wider at the base and thinner at the top, being, thereby, unlike the mantle of E. aurantiaca consisting of 2-6 layers of interwoven hyphae.
The hyphal mantle of E. lactiflua is reminiscent of the E. aurantiaca mantle in a cross-sectional view, although it is not spirally arranged as in the latter species when observed in a plan view.
The most distinctive feature of E. aurantiaca is its ornamented zygosporangial wall. Except for E. alba, the other described species of this genus form smooth-walled zygosporangia (Gerdemann and Trappe 1974; Pegler et al. 1993; Tandy 1975). The zygosporangial wall of E. alba has a minutely rugulose to almost reticulate ornamentation, frequently with branching ridges (Yao et al. 1992), whereas that of E. aurantiaca is covered with conical warts.
Additionally, the features separating E. aurantiaca from the species listed above are the lack of reactivity in Melzer’s reagent [vs. zygosporangial wall yellow to pale orange and crayfish red (9B8) in E. flammicorona and E. lactiflua, respectively], the hyaline zygospore wall (vs. melon yellow, hyaline to light yellow, and yellow in E. alba, E. flammicorona, and E. lactiflua, respectively), and the relatively narrow gametangia (20-31 µm wide vs. up to 36 µm, up to 40 µm, and up to 80 µm wide in E. alba, E. flammicorona, and E. lactiflua, respectively).
Apart from E. aurantiaca, known fungal species of this genus producing sporocarps lacking a peridium include E. acrogena Gerd., Trappe & Hosford, E. maritima Blaszk. & Tadych, and E. verrucosa Gerd. & Trappe (Blaszkowski et al. 1998; Gerdemann and Trappe 1974). Endogone aurantiaca differs in that it has no zygosporangia arranged either in chains as in E. acrogena or in clusters enclosed in an endoperidium as in E. verrucosa. Additionally, the zygosporangia of the latter two fungi are much smaller than those of the former new species. Endogone maritima produces smooth-walled zygosporangia.
Endogone aurantiaca was the first species of the genus Endogone described to form single zygosporangia in the soil (Blaszkowski 1997), although non-sporocarpic zygosporangia of E. flammicorona, E. maritima and E. lactiflua were also recovered (Blaszkowski 1989, 1993; Blaszkowski et al. 1998; see the discussion in the section “the Endogonaceae”).
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