Abstract
End‐Permian palynological assemblages worldwide are characterized by large numbers of unseparated tetrads of lycopsid microspores and occasional megaspore tetrads. These spores are assignable to the form genera Densoisporites, Lundbladispora, Uvaesporites, and Otynisporites. Transmission electron microscopy analysis of preserved sporoderm ultrastructure demonstrates that individual spores are juxtaposed or connected to each other by interlocking of the paraexospores at either the interradial contact areas or equatorial regions. The wall organization of Densoisporites, Lundbladispora, and Otynisporites confirms an isoetalean (Pleuromeiaceae) affinity. The Uvaesporites wall structure is far more complex than so far recognized in extant Selaginellales and extant and fossil Isoetales. Uvaesporites might be related to a distinct lycopsid lineage, with characteristics of rhizomorphic lycopsids and the Selaginalles.
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