Pisolithus arhizus

A fungus with a peculiar habit, irregularly shaped like a stone or animal droppings, subglobose, pyriform to clavate, 4 to 14 cm across and up to 20 cm high, with a rugose pale yellow to brown surface and a stout, woody, rooting pseudostipe anchored by abundant sulphur-yellow mycelium at the base.

The gleba in section exhibits a unique mosaic-like structure composed of pea-sized compartments (pseudoperidioles) 2 to 4 mm across, the outermost ones brown and disintegrating into powdery spores, the basal ones younger and yellowish.

Peridial hyphae filamentous, filled with brownish-olivaceous intracellular pigment, 3 to 5 µm wide, separated by gelatinization, septate.

Glebal contextual hyphae cylindrical, hyaline, 3 to 6 µm wide, septate with clamp connections.

Basidia clavate to pyriform, hyaline, highly evanescent, disintegrating completely upon spore maturation.

Spores globose, thick-walled and coarsely echinulate/verrucose, hyaline to pale yellowish, 6.5 to 9 µm in diameter (excluding ornamentation), densely covered with blunt spines or warts 1 to 2 µm high and up to 0.5 µm wide at the base, containing lipid inclusions.