Ultrastructure and affinity of Lower Carboniferous megaspores from the Moscow Basin, Russia.

Ten megaspore species isolated from Moscow Basin lignites of Lower Carboniferous (Viséan) age have been studied by scanning and transmission electron microscopy (SEM and TEM). These species belong to seven megaspore genera: Lagenicula, Sublagenicula, Crassilagenicula, Setosisporites, Zonalesporites, Caudatosporites, and Cystosporites. Megaspores of the genus Caudatosporites have only been described previously from the Duckmantian (Westphalian B); a new species is duly erected. The ultrastructure of megaspore walls from the genera Crassilagenicula and Zonalesporites has not been previously described. This study also places them in context with other contemporaneous megaspores. The study shows that during the Viséan, in the Moscow Basin, megaspores expressed a similar wall ultrastructure despite large differences in external appearance. The genus Crassilagenicula may represent a group of megaspores from plants that had evolved from those bearing gulate megaspores here typified by Lagenicula acuminata, Setosisporites brevispinosus, and Sublagenicula hirsutoida. Zonalesporites brasserti also appears to show affinities to this group, and may be representative of a plant species in a transitional state between the Lagenicula bearing lycopsids and those more isoetalean in nature.

Diversity of exine structure in Upper Carboniferous (Westphalian) selaginellalean megaspores.

Studies of wall structure in Mesozoic and Recent selaginellalean megaspores have been well documented. However, Palaeozoic examples have received minimal attention. The principal Palaeozoic megaspore genus of likely selaginellalean affinity is Triangulatisporites, extending from the Upper Devonian to the Upper Carboniferous. The particulate wall ultrastructure of a previously published Carboniferous (Duckmantian) megaspore assigned to this genus suggested that this form of wall construction may have been the ancestral wall structure of the group, an observation which posed difficulties in relating selaginellalean ultrastructure to that of other contemporaneous lycopsid megaspores. Subsequent investigation showed that the genus also contains more laminate exines similar to those of other extinct lycopsids and extant Selaginella species. Our new examples of Triangulatisporites ultrastructure from the Langsettian, Duckmantian and Westphalian D yield more information regarding early variation of wall structure within Carboniferous selaginellalean megaspores and suggest that a more laminate wall composition is at least as old as the particulate form. However, without further investigation of Lower Carboniferous forms, we are unable to state which is indeed ancestral. The laminate structure reported here and elsewhere is, none the less, more easily related to comparable ultrastructure in other groups of Carboniferous lycopsid megaspores and could suggest a link with such genera as Zonalesporites and early Lagenicula. This would be in keeping with current concepts regarding the most primitive ultrastructural type within lycopsid megaspore walls.

Nonlinear Variation in Simulated Complex Pattern Development.

Simulated spore walls manufactured from colloidal polystyrene latex, cyclohexane and water demonstrate a range of structure comparable with that occurring within the walls of Selaginella megaspores. Initial investigation of the relationship between the initiation parameters of the self-assembling simulation and its ultimate structure imply a nonlinear relationship. It is suggested that such self-assembly processes result in structure that cannot be directly mapped onto an equivalent genetic coding and that phylogenetic analyses based on self-assembled structure may differ in its conclusions from that based on DNA sequences.Copyright 1998 Academic Press Limited