Acaulospora myriocarpa

Whole Spores

This description is a combination of information obtained from the protologue (Schenck et al., 1986), type specimens, and universal patterns of morphological organization and structure in Acaulosporaceae. A living culture of this species has never been obtained by INVAM.

Aggregates (sporocarps?) range in size from small and irregular-shaped, 725 (-1050) x 525 (906) µm, to occasionally large, up to 22 X 8 mm. No peridium is formed; with aggregates often formed within soil crevices and inside roots, empty spores of other glomalean fungi, within insect carapaces, and old seed testa.

Spores also formed singly in soil or near roots. They are hyaline to white, mostly globose to subglobose, 32-90 µm diam, or cylindrical, ovoid, pyriform to irregular, (23) 28-95 (114) x (21) 28-80 (96) µm diam. As the spore forms, the saccule empties, collapses, and usually sloughs so that mature spores are sessile.

The spore wall is hyaline, 1.5-3.5 (7) µm thick; consisting of three layers (L1, L2, L3). The outer layer (L1) is rigid, 0.75- 2 µm thick. The middle layer (L2) also is rigid, 0.3-1.5 µm thick. Both L1 and L2 turn a dull yellow in Melzer’s reagent. The innermost layer (L3) is very thin, <0.3 µm.

Single spores with saccule attached	Aggregate of spores

The sporiferous saccule is globose to ovoid, 25-100×30-95 µm diam, with a single hyaline wall, 0.5-0.75 µm thick.

A pedicel links hyphal neck of the sporiferous saccule and the spore. It is hyaline, 2.8-12 long x 2.7-8 µm wide. Although not mention in the description nor observed in voucher specimens, it is likely the pedicel wall is continuous with the outer layer of the spore wall (L1).

Mycorrhizal structures stain only faintly with trypan blue, and no typical vesicles or arbuscules are observed. Based on these traits, it is possible this species is a member of Archaeosporaceae.

Reference

• Schenck, N. C., J. L. Spain, and E. Sieverding. 1986. A new sporocarpic species of Acaulospora (Endogonaceae). Mycotaxon 25:111-117.