Glomus segmentatum

Trappe, Spooner & M.H. Ivory

Spores borne in epigeous sporocarps.

Sporocarps white, 6 x 8 mm, pulvinate, firm with a basal attachment of tangled, pale yellowish brown hyphae mixed with soil, tessellated with convex, subpolygonal areas separated by grooves.

Gleba pale yellow, formed of tightly packed tough segments radiating outward from a basal pad, separating as polyhedrons with rounded outer surfaces that form the tessellate pattern of the sporocarp surface; all segment surfaces enclosed in a tightly woven, tough peridium enclosing crowded spores embedded in interwoven hyphae.

Peridial and glebal hyphae hyaline, straight or with dichotomous or perpendicular braches, (2.0-)3.9(-6.4) µm wide, of a wall (0.7-)1.1(-1.7) µm thick, staining reddish white (10A2) in Melzer's reagent. Peridial hyphae tightly subparallel alongside each radial glebal segment, but interwoven on the outer segment face. Glebal hyphae interwoven.
In PVLG
In PVLG+Melzer's reagent

SPORES hyaline to yellowish white (1A2); globose to subglobose; (65-)78(-90) µm diam; sometimes ovoid; 50-70 x 85-90 µm; with one subtending hypha.

SUBCELLULAR STRUCTURE OF SPORES consists of a spore wall comprising three layers (swl1-3).
In PVLG
In PVLG+Melzer's reagent
In PVLG+Melzer's reagent
Layer 1 evanescent, hyaline, ca. 0.5-0.8 µm thick, frequently completely sloughed.

Layer 2 finely laminate, yellowish white (1A2), (4.0-)7.1(-7.8) µm thick.

Layer 3 flexible, yellowish white (1A2), ca. 0.5-1.0 µm thick, usually tightly adherent to the lower surface of layer 2.

Generally, none of the layers 1-3 stained in Melzer's reagent. In few spores, layer 3 stained reddish white (9A2) in this reagent.
In PVLG
In PVLG+Melzer's reagent
SUBTENDING HYPHA hyaline to yellowish white (1A2); straight or curved; usually gradually widening distally, sometimes cylindrical; (9.8-)12.6(-16.4) µm wide at the spore base, 17.5-20.0 µm wide ca. 15 µm below the spore base; extending 50-200 µm to the lateral origin from glebal hyphae; generally radiating from the basal pad of the sporocarp.

Wall of subtending hypha hyaline to yellowish white (1A2); composed of three layers (shwl1-3) continuous with spore wall layers 1-3; (2.5-)3.2(-3.7) µm thick at the spore base, then gradually thins up to 0.5 µm thick.

Pore (2.2-)4.1(-5.6) µm wide at the spore base, open or closed by a straight or slightly curved septum (s) continuous with the innermost spore wall layer 3.

GERMINATION. Unknown.

MYCORRHIZAE. Unknown.

DISTRIBUTION. The holotype of Gl. segmentatum is a sporocarp originally found on a bare soil surface at the edge of a bank near Pinus carribbaea Morelet, shrubs, herbs, and a grass growing at Silver Creek F.S. in Belize (Trappe 1979). To date, it is the only finding of this fungus in the world.

NOTES. The characters of sporocarps and spores of Gl. segmentatum presented here were described based on the original description of this fungus (Trappe 1979), as well as from sections of a sporocarp and pictures obtained from Dr. F. Oehl (Institute of Botany, University of Basel, Switzerland).

The unique structure of Gl. segmentatum is its sporocarp covered with a peridium and consisting of separable polyhedrons containing crowded spores embedded in interwoven hyphae.

Other species of the genus Glomus forming sporocarps with a peridium and colourless to pale yellow-coloured spores are Gl. pubescens (Sacc. & Ellis) Trappe & Gerd. and Gl. vesiculiferum (Thaxt.) Gerd. & Trappe. However, the peridial hyphae of Gl. segmentatum do not radiate outward its sporocarps to form pubescence as the peridial hyphae of Gl. pubescens do and the largest spores of the latter species are smaller than even the smallest spores of the former fungus (Gerdemann and Trappe 1974).

The unique structures of Gl. vesiculiferum and, hence, readily separating this fungus from Gl. segmentatum are peridial thin-walled, ellipsoid to broadly clavate vesicles (Gerdemann and Trappe 1974).

REFERENCES

Gerdemann J. W., Trappe J. M. 1974. The Endogonaceae in the Pacific Northwest. Myc. Memoir 5, 1-76.

Trappe J. M. 1979. Glomus segmentatum sp. nov. Trans. Brit. Mycol. Soc. 73, 362-363.