Sistemática y vinculaciones de las Corystospermaceae H. Thomas

Abstract

"In this paper the systematic and relationships of the Corystosperrnaceae H. Thomas are analyzed. According to various authors and the present study, this family would include the following genera: Umkomasia H. Thomas, Pilophorosperma H. Thomas, Spermatocodon H. Thomas and Karibacarpon Lacey (seed-bearing organs), Pteruchus H. Thomas em. Townrow and Pteroma Harris (pollen-bearing organs), Dicroidium Cothan em. Townrow, Xylopteris Frenguelli, Johnstonia Walkom and Pachypteris Brongniart em. Harris (leaves) and Bhexoxulon Bancroft em. Archangelsky et Brett (stem). An updated synopsis of each organ is offered. It is also proposed to consider the Corystospermaceae as ""nómina conservanda"", due to its prolonged and generalized usage, and suggest as an altenative name an adequate basonym: Umkomasiaceae nom. nov., in agreement with the Botanical Nomenclature Rules (arts. 10.3 and 18.5). A reconstruction of a complete plant is given, allowing the comparison of various pairs of organs. As a consecuence, considerations are made about the possible origin of the group, its relations to similar entities and some speculations about the centre of origin of the family. It is concluded that the Corystospermaceas make an independent order (Corystospermales) within the Pteridospermopsida. They could have originated from an ancestral ptericlospermous stock in the (Upper Carboniferous?) Lower Perrnian period, in the Northern hemisphere. A differentiation process during the Permian took place due to the migration to new habitats that offered a wider range for variation. The best affinities of the Corystospermales with other groups are with the coeval Peltaspermales, with which they would constitute the subclass Peltuspermidae.