Ultrastructural analysis of the microspores from the Pennsylvanian lycophyte coneSelaginellites crassicinctusreveals a structural organization which is comparable to modern representatives ofIsoetesandSelaginella. The most prominent similarities include the presence of a para-exospore#x2014;a layer external to and largely free from the exospore, but with a similar ontogeny and staining characteristics#x2014;and a proximal multilamellated region situated at the innermost region of the exospore in the center of each interradial area. A more rigorous comparison of specific structural features indicates a higher degree of similarity withSelaginella, particularlyS. selaginoides. These results are somewhat anomalous in light of the suggested affinity ofPaurodendron, the axis which presumably bore this cone, with the Isoetales. These results stand in support of the existence of a recently proposed group of Carboniferous lycophytes which are structurally intermediate between the rhizomorphic and herbaceous types.
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