The fruit body of Thaxterogaster caesibulga is sequestrate, meaning that its spores are not forcibly discharged from the basidia, and it remains enclosed during all stages of development, even when mature. The shape of the caps ranges from irregularly spherical to like an inverted cone, sometimes with a flattened top, and they measure long by in diameter. A cobwebby silvery-grey partial veil connects the cap to the stipe. The outer skin of the cap (the pellis) is lavender (mixed with tan in mature specimens) with a finely hairy texture. Remnants of the universal veil are readily rubbed off with handling. The flesh is translucent white to cream and thick. The internal spore-bearing tissue of the cap (the hymenophore) is pale brown at first, but darkens as the spores mature. A slender, silvery lavender stipe extends into the fruit body through its entire length; it measures long by thick. Young fruit bodies have no distinctive or odor, but develop a pungent smell as they mature; their taste is somewhat farinaceous (similar to freshly ground flour). The spores are egg-shaped to roughly elliptical and measure 8.7–11 by 4.8–6.5 μm. They are densely covered with nodules up to 0.5 μm high. The thin-walled basidia (spore-bearing cells) are hyaline (translucent), club-shaped to cylindrical, four-spored, and have dimensions of 26–39 by 5–8 μm.
