Zygosporangia occur in compact sporocarps, rarely in loose aggregates or singly in the soil.
SPOROCARPS ovoid to irregular; 1-2.5 x 3-8 mm; composed of a peridium surrounding up to hundreds randomly and compactly positioned zygosporangia individually enveloped by a hyphal mantle.
Peridium white, pubescent in young sporocarps, gradually deteriorating with age and, thereby, partly or completely revealing the zygosporangia present.
Mantle (5.0-)11.7(-20.0) µm thick; consists of interwoven, hyaline hyphae; (2.5-)10.7(-22.5) µm wide; mantle hyphae adherent to zygosporangia more compactly interwoven than those positioned in the outer region of the mantle, forming a unit sheath easily separating from zygosporangia; hyphae of the outer mantle layer branched and interwoven with those of neighboring zygosporangia. In a cross-sectional view, the hyphal mantle consists of many tightly adherent layers. When seen in a plane view, the mantle resembles a cerebrum.
In Melzer’s reagent, mantle hyphae stain light orange (6A5) to pale red (8A3). However, the staining reaction always is darker in the inner region than in the outer one of the mantle. Red reaction of the mantle hyphae in Melzer’s reagent also occurs in E. alba (Petch) Gerd. & Trappe (Yao et al. 1992), E. pseudopisiformis Y. J. Yao (Yao et al. 1995b), E. maritima Blaszk. et al. (Blaszkowski et al. 1998), and Youngiomyces carolinensis Y. J. Yao (Yao et al. 1995a).
ZYGOSPORANGIA melon yellow (5A6) to dark orange (5A8); globose to subglobose; (90-)127(-170) µm diam; sometimes ovoid or broadly ellipsoidal; 100-110 x 120-160 µm; with a circular, 13.5-15.0 µm diam, or slightly ellipsoidal, 8.8-10.0 x 12.5-16.3 µm, and raised pore at the junction of the larger of the two gametangia.
In PVLG+Melzer's reagent
Zygosporangial wall (zlw) consists of a single, smooth, melon yellow (5A6) to dark orange (5A8) layer, (1.5-)2.1(-2.7) µm thick.
Zygospore wall (zew) single, smooth, hyaline, (0.7-)2.4(-4.1) µm thick, easily separating from the zygosporangial wall.
GAMETANGIA hyaline; subglobose, ellipsoidal, prolate or irregular; 32.5-52.5 µm wide, 55.5-110.0 µm long, of unequal size, placed one near another, rarely absent.
Gametangial wall smooth, 0.7-1.7 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.
In Melzer’s reagent, zygosporangia, and gametangia stain, crayfish red (9B8), and pale red (8A3) to pastel red (8A4), respectively.
MYCORRHIZAE. Endogone lactiflua has occurred in the field among ectomycorrhizal roots of Pinus sylvestris L. and those with vesicular-arbuscular colonization coming from an adjacent grass (Blaszkowski et al. 2004). This fungus failed to form new zygosporangia and mycorrhizae in pot cultures with P. sylvestris.
Walker (1985) found sporocarps of E. lactiflua associated with ectomycorrhizae of P. contorta Dougl. ex Loud. cultivated in boxes filled with sphagnum peat in a greenhouse of Scotland.
DISTRIBUTION. Of the ca. 2200 soil-root samples so far collected from under ca. 110 plant species growing in different regions of Poland, spores of E. lactiflua have been found only in one sample (Blaszkowski et al. 2004). This sample was taken under P. sylvestris growing in a forest dune carried away ca. 500 m from the bank of the Baltic Sea located near Jastrzebia Góra (55o18’N, 17o54’E) in northern Poland.
Endogone lactiflua probably has a worldwide distribution. This fungus has been found to be widely distributed from the sea level to subalpine zones of the Pacific Northwest, USA (Gerdemann and Trappe 1974). Berch and Fortin (1984) revealed E. lactiflua under Sphagnum growing in Quebec, Canada. Endogone lactiflua had many times been encountered in the United Kingdom (Godfrey 1957; Hawker 1954; Pegler et al. 1993; Walker 1985), where it has been considered to be the most commonly occurring species of this genus (Pegler et al. 1993). Additionally, this fungus has been recorded in Portugal (Trappe and Gerdemann 1972), Denmark (Lange 1956; Lange and Lund 1954), Hungary (Szemere 1965), Austria, Germany, and the former USSR (Lawrynowicz 1979).
NOTES. The distinctive properties of E. lactiflua are its sporocarps with many spores individually surrounded with a hyphal mantle, the coloured zygosporangial wall being thinner than the colourless zygospore wall, as well as the reactivity of the mantle hyphae, the zygosporangial wall and gametangia in Melzer’s reagent.
Although gametangia are usually present in most of the E. lactiflua specimens examined in this study, they frequently are difficult to see because of their cover by the hyphal mantle. One of the two co-occurring gametangia always is larger, usually has a thicker wall, and is associated with a pore of the zygosporangium. The second gametangium has no contact with the zygosporangium. This agrees with the Trappe and Gerdemann’s (1972) finding that zygosporangia of E. lactiflua develop from the tip of the larger gametangium, as do those of E. flammicorona Trappe & Gerd. and E. maritima (Blaszkowski et al. 1998).
Most of the sporocarps found contain hundreds spores, although aggregates consisting of two spores and single spores were also isolated. Single zygosporangia and those arranged in small aggregates were also found to be formed by E. aurantiaca Blaszk., E. flammicorona (Blaszkowski 1993), and E. maritima (Blaszkowski et al. 1998; see the discussion in the section “the Endogonaceae”).
The fungal species of the genus Endogone producing spores most similar morphologically to those of E. lactiflua are E. flammicorona and E. maritima. All the species form yellow-coloured and individually mantled spores with a zygosporangial wall thinner than that of a zygospore. The main differences separating the three fungi reside in the ability to form sporocarps, morphological and biochemical properties of their hyphal mantle and spores, as well as in features of their gametangia.
Spores of E. lactiflua and E. flammicorona mainly occur in large and compact sporocarps surrounded with a peridium (Gerdemann and Trappe 1974). The sporocarps usually contain many (even hundreds) spores. In contrast, most spores of E. maritima are grouped in small, 2-3-spored sporocarps lacking a peridium and have also frequently been found singly in the soil (Blaszkowski et al. 1998).
While the hyphal mantle of spores of E. lactiflua consists of many layers of tightly interwoven hyphae appearing netted in a cross-sectional view, that covering E. flammicorona spores is composed of a single layer of spirally arranged hyphae resembling flame-shaped projections in a cross section (Gerdemann and Trappe 1974). Both the hyphal mantle and spores of E. lactiflua stain intensively red in Melzer’s reagent. In contrast, the zygosporangial wall of E. flammicorona becomes only yellow to pale orange in this reagent (Gerdemann and Trappe 1974).
The gametangia of E. lactiflua are present in most specimens of this fungus and are thick-walled at maturity, and those of E. flammicorona are ephemeral, thin-walled, and generally are invisible on mature spores (Gerdemann and Trappe 1974). Additionally, the gametangia of the former fungus are markedly wider [up to 52.5 µm, Blaszkowski, pers. observ.; up to 65(-80) µm, Gerdemann and Trappe 1974] than those of the latter species [up to 35(-40) µm, Gerdemann and Trappe 1974].
Apart from the differences listed above, the distinguishing property of E. maritima zygosporangia is their non-reactivity in Melzer’s reagent (Blaszkowski et al. 1998; vs. intensively red staining in E. lactiflua when mounted in this reagent).
Other related fungi producing zygosporangia surrounded with a hyphal mantle are E. aurantiaca, Y. multiplex (Thaxter) Y. J. Yao, and Y. stratosus (Trappe, Gerd. & Fogel) Y. J. Yao.
The conical warts ornamenting the surface of the zygosporangial wall of E. aurantiaca (Blaszkowski 1997) most contrast with the smooth-walled outer surface of E. lactiflua zygosporangia.
The basis for the erection of the genus Youngiomyces Y. J. Yao and the new combinations Y. multiplex and Y. stratosus from E. multiplex Thaxter and E. stratosa Trappe, Gerd. & Fogel has been the formation of zygosporangia from gametangia separated from each other (Yao et al. 1995a). In E. lactiflua and all other members of the genus Endogone, zygosporangia bud from the tip of the larger gametangium always associated with the second, smaller one.
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