Elater-bearing spores, once thought to be relatively rare in Upper Carboniferous sediments, are now known to have been produced by many Pennsylvanian sphenophytes. Specimens ofElaterites triferensWilson are radially symmetrical, trilete and possess three circinately-coiled elaters attached to the distal surface by a triangular truss. At the ultrastructural level, the sporoderm consists of two layers: a uniformly thickened exospore, and a thicker, irregularly shaped perispore. The perispore is bilayered with the outer, homogeneous layer forming a series of ridges, and an inner granular layer that is formed by expansion during development. Elaters possess three distinct layers. A comparison of the spores ofElateritesandEquisetumreveals a number of morphological and ultrastructural differences that provide an opportunity to trace the evolution of the sporoderm in these closely related taxa.