Spores of Glomus spp. develop blastically at the end of a sporogenous hypha, although intercalarily spore formation has also been reported (e. g, Declerck et al. 2000). In most species, the sporogenous hypha develops from extraradical hyphae of mycorrhizal roots. Spores of some species, e. g., Gl. aggregatum, Gl. intraradices, frequently occur inside roots (Schenck and Smith 1982). Glomus aggregatum and Gl. microaggregatum additionally produce inner spores from a sporogenous hypha arising from the subtending hypha of the parent spore (Blaszkowski 1991; Koske 1985; Koske et al. 1986a; Schenck and Smith 1982).

The surface of spores of Glomus spp. may be smooth (in most species) or differently ornamented (e. g., Gl. multiforum, Gl. pustulatum; Blaszkowski 1994a; Blaszkowski and Tadych 1997; Koske et al. 1986b). Some species produce spores enveloped in a hyphal mantle consisting of interwoven (e. g., Gl. mortonii, Gl. fuegianum; Bentivenga and Hetrick 1991; Blaszkowski et al. 1998) or dichotomously branched (Gl. corymbiforme; Blaszkowski 1995) hyphae.

In water
Most species of the genus Glomus produce spores singly in the soil. Other taxa form more or less compact spore aggregates (e. g., Gl. minutum, Gl. aggregatum; Blaszkowski et al. 2000; Blaszkowski 1991; Koske 1985) or sporocarps (e. g., Gl. coremioides, Gl. fuegianum, Gl. mosseae; Almeida and Schenck 1990; Blaszkowski et al. 1998; Gerdemann and Trappe 1994) consisting of spores and a peridium. The formation of the peridium may precede the spore origination or the peridium expands together with the developing spores, as e. g. in Gl. mosseae and Gl. coronatum (Giovannetti et al. 1991). Some spores of Gl. gibbosum develop within a hyphal mantle without an opening (Blaszkowski 1997).

Although fungi of the phylum Glomeromycota, except for Geosiphon pyriformis, are considered to form obligatorily arbuscular mycorrhizae in mutualistic associations with living plants (Morton and Benny 1990; Schüßler et al. 2001), the formation of spores associated with both mycorrhizal roots and non-root habitats by, e. g., Gl. fuegianum (Blaszkowski et al. 1998; Pegler et al. 1993), Gl. fasciculatum, and Gl. sinuosum (Gerdemann and Trappe 1974; Koske, pers. comm.) indicate that some species are facultative symbionts (Blaszkowski et al. 1998).

All members of the genus Glomus form spores with only one wall including at least two layers, of which the structural layer consists of many sublayers (laminae). The outer layer or layers adherent to the laminate layer frequently slough(s) with age. In some species, e. g., Gl. claroideum and G. etunicatum, the outermost layer stains red in Melzer’s reagent (Stürmer and Morton 1997). A few species, e. g., Gl. claroideum, Gl. lamellosum and Gl. gibbosum, produce a flexible inner layer developing from the subtending hypha; this layer frequently is adherent to the lower surface of the laminate layer and, therefore, it usually is difficult to see (Blaszkowski 1997; Blaszkowski et al. 2002; Dalpé et al. 1992; Stürmer and Morton 1997). Of the described species, the flexible inner spore wall layer of only Gl. lamellosum stains in Melzer’s reagent (Blaszkowski et al. 2002); however, this property also occurs in some other undescribed species (Blaszkowski, pers. observ.).


The wall layers of a subtending hypha are continuous with spore wall layers. During ontogeny, they differentiate at the same time and rate. At the end of spore development, the lumen of the subtending hypha usually becomes closed by either (1) a curved septum continuous with the innermost lamina of the laminate spore wall layer, (2) an invaginated flexible innermost layer, (3) an amorphous plug, (4) thickening subtending hyphal wall, or (5) a combination of the structures mentioned.


Spores of the genus Glomus germinate by emergence of the germ tube through either the lumen of the subtending hypha (most species) or the spore wall. Germination by both the lumen and spore wall was also observed.

The mycorrhizae of Glomus spp. consist of arbuscules, vesicles (not always formed), and intra- and extraradical hyphae. Arbuscules have cylindrical or slightly flared trunks with branches progressively tapering in width towards tips. Vesicles usually are thin-walled and ellipsoid. Intraradical hyphae usually spread along roots and frequently form Y-shaped branches, H-shaped connections, and coils. Coils mainly occur at entry points.

In roots of Plantago lanceolata L.

The genus Glomus is the most numerous and diverse group of fungi in the Glomeromycota. It includes ca. 53% of all arbuscular fungi described to date and has initially been divided into three phylogenetic groups, Glomus groups A, B, and C (Schwarzott et al. 2001). Walker and Schüler (2004) raised the Glomus group C to the rank of a genus, Diversispora, in the newly erected family Diversisporaceae and order Diversisporales, now still including the families Acaulosporaceae, Entrophosporaceae, Gigasporaceae, and Pacisporaceae (Blaszkowski 2003; Walker and Schüler 2004; Sieverding and Oehl 2006). Whereas the Glomus group B was phylogenetically uniform, the Glomus group A was considered to contain two or three subclades (a-c), of which the subclade c included only an undescribed Glomus W3347 (Schwarzott et al. 2001). The subclade a was represented by, e. g., Gl. mosseae, and the subclade b by, e. g., Gl. intraradices. According to Schüler et al. (2001), Glomus group A and Glomus group B will be separate families, of which the family Glomeraceae will represent Glomus spp. related to Gl. microcarpum, the type species, when its phylogenetic position is recognized.


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