Developmental stages	Mature spores

COLOR: Red-orange (0-50-60-5) to dark red- brown (40-50-70-10).
Immature spores initially are cream-colored and gradually acquire an
orange tint as the spore wall begins to differentiate (see photo).

SHAPE: Globose to subglobose, sometimes irregular.

SIZE DISTRIBUTION: 240-360 µm (mean = 289 µm, n = 58).

SPORE WALL: Three layers (L1, L2 and L3) are usually evident, with the outer layer continous with the wall of the neck of the parent sporiferous saccule. The inner two layers are synthesized sequentially as the spore forms on the neck of the saccule. A third layer homologous with that in spores of other large ornamented species (e.g., A. tuberculata).

L1: Hyaline, 2-2.4 µm thick; degrading and sloughing with collapse and dehiscence of the sporiferous saccule (see first photo above).

L2: A layer that thickens with synthesis of orange-red sublayers (or laminae); 9-18 µm (mean = 14.6 µm ) thick at maturity. Initially a single layer, 2-4 µm thick, forms in undulations that establish the shape and depth of surface concave depressions (or pits), with additional sublayers forming horizontally beneath to establish a an underlying base (see photos above). Depressions are circular to ovoid, 8-12 µm across and 0.5-3 µm deep in the mature layer. This layer does not produce any reaction in Melzer's reagent.

L3: A layer that forms with synthesis of additional concolorous sublayers that are not readily distinguishable in PVLG, but more evident in Melzer's reagent because it produces a dark red-brown reaction. This layer often is fused with L2, but sometimes separates (see photo above), 3-5 µm thick when measurable. This layer may be homologous with an inner separate laminate layer (L3) in spores of A. koskei and A. laevis.

Spores mounted in PVLG		Spores mounted in PVLG + Melzer's Reagent (1:1 v/v)

GERMINAL WALLS: Two hyaline flexible inner walls (gw1 and gw2) are present. They can be seen only after spores have completely cleared when mounted in PVLG or Melzer's reagent, which can take as long as 30 days.

GW1: Consisting of two adherent layers (L1 and L2) are formed, both are of near-equal thickness, ranging from 0.6-1.0 µm thick. This wall forms completely independent of the spore wall and thus has no direct developmental connection with it.

GW2: Consisting of two adherent layers (L1 and L2) are formed that together are 5-12 µm when measured in PVLG. L1 is hyaline, 1.5-2.2 µm thick with granular excresences (or "beads") that tend to become dislodged and float away when pressure is applied to it. These "beads" are stabilized after preservation in formalin, but otherwise may be absent on mounted spores within a few months of storage. L2 is hyaline and somewhat plastic (probably equivalent to a "coriaceous" wall using traditional terminology). It is 2-10 µm thick in PVLG-based mountants, staining pinkish red (20-80-60-0) to a reddish-purple (40-80-60-0) in Melzer's reagent.

Isotype	INVAM

COLOR: White to cream when immature, hyaline when emptied of contents.

SHAPE: Mostly globose to subglobose.

SIZE DISTRIBUTION: 260-320 µm, mean = 282 µm

SACCULE WALL: A single hyaline layer with fine sublayers; the outermost sublayers appearing somewhat flakey; 3.5-4 µm thick. In the isotype (see left photo above), flakiness of the saccule surface was more pronounced and the wall was thicker (4-10 µm).

SACCULE NECK: Tapering from the saccule to the region of spore attachment; saccule neck wall hyaline and 1.8-2.2 µm thick

DISTANCE FROM SACCULE TO SPORE: Not measured in spores examined thus far.

NOTES

Janos, D. P. and J. M. Trappe. 1982. Two new Acaulospora species from tropical America. Mycotaxon 15: 515-522.