A novel gymnosperm reproductive organ from the Jurassic of China

Abstract

A feature that distinguishes angiosperms from their gymnosperm peers is that the ovules of angiosperms are enclosed before pollination. Theoretically, the angiosperms were derived from fossil seed plants that have their ovules not enclosed before pollination (gymnosperms). The origin of angiosperms is essentially a process in which the former exposed ovules got enclosed. Although various fossil taxa with different extent of ovule-protection have been documented in the Mesozoic, the morphological gap between angiosperms and gymnosperms is still far from bridged. To narrow down such a gap, here we report a novel fossil gymnosperm, Paradoxa n. gen., demonstrating a mosaic feature comparable to angiosperms in certain aspects from the Jiulongshan Formation (Middle-Late Jurassic) of Inner Mongolia, China: pollen grains trapped inside the female unit imply that Paradoxa is a gymnosperm, while several characters (especially long apical process and partially covered ovule) make it more comparable to angiosperms. It is noteworthy that, different from Caytonia, Umkomasia and Petriellaea (all in the so-called seed ferns), Paradoxa’s Bau-plan is more comparable to that of the basalmost angiosperm Amborella, suggesting a possible provenance of angiosperm carpels.