EVIDENCE FOR HYDROPHILY IN A CARBONIFEROUS MEDULLOSAN ILLUMINATES POLLINATION MODE OF EARLY SEED PLANTS (Invited Presentation)

The advent of seeds was a major innovation in plant evolution that eliminated the need for environmental water for fertilization and enhanced the potential for reproduction among plants living in drier terrestrial environments. However, with the advent of the seed habit came the requirement for pollination to bring the developing male gametophyte inside the pollen grain into proximity with the female gametophyte inside the ovule. Living seed plants largely rely on animals, most commonly insects, or wind for pollination; it has been inferred that the earliest seed plants were wind pollinated as well. An alternative hypothesis that has received little consideration is that pollination in the earliest seed plants, like fertilization in seed plant ancestors, was also intimately connected to the availability of environmental water. Here, we test this possibility of water mediated pollination in Stephanospermum konopeonus, an early seed plant that has unusually large Monoletes-type pollen. We constructed a digital 3D model of the Stephanospermum ovule and used computational fluid dynamics to simulate water flow around it. This case study indicates that water pollination, which is clearly secondary among living seed plants, likely operated in Stephanospermum and perhaps other members of the extinct seed plant order Medullosales. This raises the possibility that environmental water may have been more involved in early seed plant reproductive processes than has previously been envisaged.