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Brief Summary

    Youngiomyces spp.
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    Youngiomyces(Y.J. Yao 1995) is a genus of fungi in the family Endogonoceae of the phylum Zygomycota.The genus contains about 4 different species predominantly found in Europe (Spain), Australia, and North America (USA).

    Species of Youngiomyces form structures called sporocarps – fruting structure measuring between 0.5 – 1.3 cm in diameter, containing densely interwoven hyphae and zygospores. Sporocarps have been found in shallow soils rich in organic matter, below mosses or leaf-litter.

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Distribution

    Distribution
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    Before 1996, Youngiomyces species had only been described from herbarium specimens from Australia and North America (North Carolina). However, in 1997 Vidal and colleagues described a Youngiomyces multiplex specimen in Spain that constitutes the first reference in Europe (Vidal et al., 1997).

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Morphology

    Morphology
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    Youngiomycesspecies are sporocarpic—they form a fruiting body termed asporocarp on which spore-bearing structures are borne. The zygospores, adiploid reproductive stage in thelife cycle, develop within gametangia. The sporocarps can be hypogeous or epigeous with variable shapes with or without a peridium. Sporocarps are normally white or yellow but they can also become orange or reddish (Figure 2). Most of the fruiting body surface is granulous, with uneven protrusions of zygosporangial clusters; some parts are embedded with soil substrate or covered with irregular hyphal patches (Yao et al., 1995). Each sporocarp is formed of around one hundred granules with spherical and/or globose shape, internally deformed because of the mutual compression with a diameter between 450-1000 μm.

    The zygospores of Youngiomyces spp. are usually yellow, spherical or oval, with a diameter of about 75 um and a zygosporangial wall of the same color (4-7.5 μm). Its interior is occupied by numerous spherical gútulas (Figure 3A & 3B). The zygospores are developed inside a hyaline sporangiothecium that covers 2-4 μm. After the sporangiothecium collapses the zygospore is normally released. In almost all species, the eusporium (zygospore wall) and sporangiothecium have two openings, rarely three and are difficult to locate under the microscope, which are the points of insertion of gametangia (Figure 3C & 3D). In Youngiomyces multiplex and carolinenses, the sporangiothecium is covered by a compact hyphal mantle of 5-10 μm of thickness (Figure 3F).

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General Ecology

    General Ecology
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    As its closest relatives in the Endogone genus, some Youngiomyces species have been found in soils rich in organic matter, below mosses and leaf-litter. Youngiomyces spp. are considered saprotrophs although they might also be ectomycorrhizal as other members of the Endogonaceae family (Warcup, 1990). Indeed, Trappe and colleagues described the Pseudotsuga genus as the mycorrhizal host of Youngiomyces stratosus in the pacific northwest of the United States (USDA, 2015). Due to its limited distribution little is know about its ecological role, however, as other saprotrophs they might be important in the recycling of organic matter.

    Most members of the Endogonaceae family produce an odor that attracts small mammals and encourage them to eat their fruiting bodies, and so spread their spores by their feces (Alexopoulos, Mims, & Blackwell, 1996). The sporocarp of some Youngiomyces spp. have been described as having the odor of burnt sugar which may be playing the attracting role mentioned above. Although, it has not been studied for all the species (Vidal et al., 1997).

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Taxonomy

    Taxonomy
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    Some species of the Youngiomyces genus were first described as members of the sister taxa Endogone. Endogone was initially described by Johann Heinrich Friedrich Link in 1809. Roland Thaxter revised the taxonomy of the family Endogonaceae in 1922 and recognized only four genera: Endogone,Sphaerocreas,Sclerocystis, andGlaziella. Only until 1994 Yi-Jian Yao and colleagues restricted Endogone to those species whose gametangia are joined together with only one attachment site at the zygosporangium base (Figure 1A) (Yao, Pegler, & Young, 1995). Those taxa in which the gametangial elements (suspensors) are separated by the sporangiothecium (Zygosporangial wall) between them were transferred to a new genus, Youngiomyces (Figure 1B) (Benny, 2008)



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    Julian Bello
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    34817510