The reproductive biology of glossopterid gymnosperms—A review

Abstract

We review recent advances on glossopterid reproductive biology and their implications for seed plant phylogeny and the ecology of this widespread Permian Gondwanan group. Microsporangiate organs are interpreted to have been arranged in loose compound cones—an organization that evokes comparisons with Ginkgoales, Cordaitales and early conifers. The pollen was typically taeniate, bisaccate, and primarily adapted to wind dispersal. The diverse ovuliferous organs generally incorporated some form of marginal flange or wing. In most cases, the wing was probably protective, wrapping around the ovules during early development. However, we postulate that some conspicuous flanges were potentially analogous to angiosperm petals, functioning as corolla-like guides to attract insect pollinators. The arrangement of seed-bearing polysperms adnate to the subtending leaf to form a fertiliger in glossopterids represented another means of protecting the ovules. In some cases, highlighting the polysperm against the attached leaf might have increased the showiness of the ovule-bearing part for pollinators. In other cases, detachment of the fertiliger may have aided anemochory by retarding seed fall through rotation analogous to dispersal in extant Tilia. The microgametophyte in glossopterids is characterized by a short, weakly branched, haustorial tube, and the release of motile sperm cells. At least some seeds of glossopterids express polyembryony. Mature seeds possessed various micropylar modifications for the entrapment of pollen, and winged or bulbous expansions of the outer integument to aid anemochory or possibly hydrochory. Vegetative regeneration as a response to damage occurred via epicormic buds and possibly by the development of lignotubers.