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Tulasne and Tulasne, 1845 |
| Etymology: | Latin, "a ball of yarn" |
| Description: | Member species have all characters of the family Glomaceae except that spores are not formed in a highly organized matrix originating from a columnar base. |
| Type species: | G. microcarpum Tul. & Tul. |
Development of spores proceeds by blastic expansion of a hyphal tip as shown below. Intercalary spore formation also has been reported in some species, but its occurrence is much rarer. Outer layers of the spore wall often slough as the spore ages (in soil or in pot culture storage). Developmentally, these layers are the first components of the spore wall to form in juvenile spores. Usually, the outermost layer is mucilagenous, a property which appears to correlate with a dextrinoid (red) reaction in Melzer's reagent.
The hypha subtending the spore differentiates at the same rate and synthesizes the same component layers as that found in the spore wall. In some species the subtending hypha of mature spores is so thin that it is hard to see or separates from the spore. To separate these sessile-appearing spores from those in Acaulosporaceae, one only needs to examine for completely separated flexible inner walls in crushed spores mounted on a glass slide (present in fungi in Acaulosporaceae, absent in Glomus).
Glomus species are the most diverse in Glomales, and we attribute this diversity to a high degree of plasticity in number, phenotypes, and position of layers in the spore wall. In all other genera, variation in spore wall structure must much more constrained.