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This
description is a combination of information obtained from the protologue (Koske
and Walker, 1986), type specimens, and universal patterns of morphological organization
and structure in Glomaceae. Spores pictured at right are of an accession from
CIAT which failed to establish when deposited in the collection.
Spores formed singly, or in pairs or triplets adhering to each other by common peridial hyphae; globose to subglobose, 150-260 x 150-270 µm, excluding the peridium; orange brown to rich red-brown in color.
The spore wall is encased in an outer peridium, which consists loosely interwoven hyaline to yellow-brawn, coenocytic or sparsely septate, thin-walled hyphae, 5-50 µm broad, bearing numerous terminal or intercalary globose to ovoid, pale yellow-brown or hyaline vesiculate swellings Glomus-like in shape and form, that either are empty, or have granter, orange-brown contents. Vesiculate swellings 12-65 x 12-75 µm, with walls 1-2.5 µm thick, consisting of a thin, hyaline outer unit wall, and a thicker, slightly colored inner laminated wall. As the spores age, the peridial hyphae loose their contents and collapse to form a tight envelope of indistinctly plectenchymatous tissue.
The spore wall consists of three layers (L1, L2 and L3). The outer layer (L1) is rigid, hyaline to pale yellow-brown, 0.5-3 µm thick. The middle layer (L2) is made up of finely adherent sublayers (or laminae), orange-brown to red-brown in color; 6-30 µm thick. Koske and Walker (1986) describe 1-2 additional thin layers, but such variation suggests that it is a single layer (L3) with sublayers of varying number and thickness (such as that observed for the innermost layer of G. claroideum). This layer appears to vary in thickness from 1-3 µm. It is described as being hyaline, but more likely is concolorous with L2 of the spore wall. Its position relative to the wall of the subtending hypha is not clear.
The subtending hypha is straight or recurved; usually constricted proximally but occasionally straight or funnel-shaped; 15-27 µm wide at the spore base, 18-37 µm at the widest point, with the wall 2-8 µm thick. Wall structure of the subtending hypha is not described, except to be "thick-walled proximally, but with the wall thickness rapidly diminishing from the point of connection to a thin-walled, hyaline, sparsely septate, parent hypha".
The occlusion appears to be either thickening of the innermost sublayers of L2 of the spore wall or a granular plug. Koske and Walker (I1986) described the subtending hypha as appearing to be "inserted into the spore wall".
Spores appear to closely resemble those of G. tortuosum. Koske and Walker (1986) describe G. tortuosum spores as being smokey grey-brown color under a stereomicroscope, while those of G. globiferum typically are orange-brown to red-brown. This may have been true of their specimens, but G. tortuosum accessions in INVAM are of similar color to G. globiferum. The only other discrete difference appears to be the vesiculate swellings in the peridium, and the phylogenetic significance (heritability, stability) of this trait is poorly defined. A living culture of this species has never been obtained by INVAM. It is possible these two species are synonymous.
REFERENCES
Koske, R. E. and C. Walker. 1986. Glomus globiferum: a new species of Endogonaceae with a hyphal peridium. Mycotaxon 26:133-142.