The structure of the sporopollenin wall of fossil megaspores can be usefully applied to the determination of morphological similarities and differences between species and genera, which in turn can aid determinations of botanical relationships. Nine species belonging to seven genera of lycopsid megaspores from European Mesozoic successions that have been examined in thin section under a transmission electron microscope are discussed in this paper. Of these, seven are considered to be referable to the Selaginellales, namely Bacutriletes pragensis, Echitriletes zemechensis, Erlansonisporites sp. ‘pseudomoravica’ type, Horstisporites cenomanicensis, Kerhartisporites kleinii, K. srebrecensis, Ricinospora sp. and Verrutriletes maloninensis. The structure of the exospore of Aneuletes patera, an alete species of hitherto uncertain affinity, also suggests that this has selaginellalean origins. The construction of the wall of Echitriletes lanatus, however, resembles that of representatives of the Isoetales and implies derivation from a family within, or related to, one or other of these lycopsid orders that is now extinct. Along with aspects of their gross morphology, significant differences between the structure of the exospore of E. lanatus and E. zemechensis suggest that they do not belong in the same morphological genus. The value of the differentiating Kerhartisporites from Erlansonisporites is questioned.

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