The spore sac contains the gleba, which is composed of a pseudocolumella, unbranched threads (the capillitium), the spore-bearing cells (basidia) and the spores themselves; all of these microscopic elements have certain characteristic features that help distinguish G. triplex from other superficially similar earthstars.
The spores are spherical, and 3.5–4.5 µm in diameter. They are covered with short narrow abruptly terminating projections of a translucent (hyaline) substance, which turn a pale cinnamon brown in potassium hydroxide, and a dark dull brown (nearly sepia) when stained with iodine. The capillitium is made of what appears to be encrusted cylindrical filaments 3–6 µm in diameter, of a color varying from hyaline to dull yellowish brown in potassium hydroxide, and yellowish in iodine; its walls are thickened to the point where the interior (lumen) appears as only a line. Either two or four spores are attached to the basidia, and the sterigmata (extensions of the basidia that attach the spores) are long, up to 20 µm. Geastrum triplex does not have cystidia.