Reproductive organs of fossil plants and their spores and pollen: Aspects, trends and perspectives

Here we describe Pachytesta duquesnei sp. nov., a Carboniferous medullosalean ‘seed’ (middle Pennsylvanian, Bruay Formation, slag heap of Lens-Liévin district, Pas-de-Calais department, France), attributed to a female reproductive structure of ‘seed ferns’ of the genus Alethopteris, very frequent in the same layers. The peculiar micropylar extension of the new ‘seed’, as long as half of total ‘seed’ length, is compared to the other known medullosalean/trigonocarpalean ‘seeds’, including Stephanospermum, but also to Trigonocarpus considered as ‘seed’ casts present in several localities in Western Europe. The attribution of Whittleseya elegans as male organs of an Alethopteris sp. is also discussed. The latter occurs is present in the same locality with Pachytesta duquesnei sp. nov. We discuss the possible function of the extremely elongate micropylar extension of Pachytesta duquesnei sp. nov., suggesting it is unlikely adapted to a pollination-drop mechanism, but rather could be linked to a protection mechanism against arthropod predators and/or to a highly specialized pollination mechanism either by very tiny insects entering these ‘seeds’ through this tube (with figs and fig wasps as modern analogues) or an insect with elongate mouthparts able to go inside the ‘seed’ (with tube flower and moths with extremely long proboscis), to feed and transport pollen at the same time.