MORPHOLOGICAL REASSESSMENT OF SOME ZONATE AND CORONATE MEGASPORE GENERA OF MAINLY POSTPALEOZOIC AGE

An analysis of Mesozoic and Tertiary megaspore assemblages from NW Europe has shown that several zonate and coronate genera are not adequately differentiated on the basis of their original diagnoses. A number of the species that have been described previously, and a few new forms recently encountered, display characters that are attributable to more than one genus. The genera considered are Auriculizonospora, Capillisporites, Dijkstraisporites, Flabellisporites, Henrisporites, Herbosisporites, Membranisporites, Minerisporites, Pavlovisporites (a monotypic Permian form), Paxillitriletes, Sepisporites, Tenellisporites and Triangulatisporites. A comparison of the morphology of all of the species within this group that are known to us has enabled a reassessment of the criteria on which they can be distinguished. As a result (1) Auriculizonospora is reinstated as a genus that is distinct from Minerisporites, (2) the diagnoses of these two genera, Dijkstraisporites, Paxillitriletes and Tenellisporites are emended, (3) Membranisporites is placed in synonymy with Paxillitriletes, (4) six species are newly combined with other genera, and (5) one is renamed. The nomenclatural changes are as follows: Dykstraisporites (al. Minerisporites) pterotus (Singh, 1983) comb. nov., ?Flabellisporites (al. Tenellisporites) spinatus (Peake, 1968) comb. nov., Minerisporites archangvillarae nom. nov. (new name for Minerisporites elegans Archangelsky and Villar de Seoane, 1989, a junior homonym of M. elegans Li Wenben and Batten, 1987), Minerisporites (al. Henrisporites) levis (Lachkar, 1979) comb. nov., Minerisporites (al. Dijkstraisporites) psilites (Gunther and Hills, 1972) comb. nov., Paxilitriletes (al. Triletes) ales (Harris, 1935) comb. nov., and Paxillitriletes (al. Triletes) samarus (Dijkstra, 1951) comb. nov. Although a few forms remain difficult to place because of their ''intermediate'' character, it is now possible to refer the majority to genera with greater confidence than hitherto. The chances of both taxonomic and nomenclatural confusion, and of biostratigraphic misinterpretation should, therefore, be reduced in the future. Most of the genera are thought to have isoetalean origins but the three Triassic species that have been referred to Triangulatisporites, and some of the other species from this geological period may well be selaginellalean spores.