Umkomasia is a cupulate ovule-bearing organ belonging to the Corystospermales, a small group of pteridosperms known from the Triassic. Since their initial description, these reproductive structures have been known only from compressions. Although many species of Umkomasia have been described, important details of morphology have remained ambiguous due to the lack of anatomical information. Conflicting interpretations of morphology, as well as missing information on key characters, have resulted in poor resolution of the position of the corystosperms in seed plant phylogeny. Anatomically preserved Umkomasia has recently been identified for the first time in permineralized peat from the early Middle Triassic of Antarctica. These specimens provide the opportunity to correlate the morphological details of Umkomasia with anatomical information. Umkomasia is a determinate cupulate branch with helically arranged, recurved, pedicellate cupules, each of which bears one to two abaxially-attached unitegmic ovules. Cupules are ovoid and either bilobed with elongate ventral and dorsal apertures or unlobed with an elongate ventral aperture. The cupule cortex is two-zoned and includes sclerified cells and abundant secretory cavities. Ovules are small, orthotropous, broadly attached basally, and also possess secretory cavities in the thin integument. The bifid apex of the integument extends past the cupule lobes. The cupulate branch is ovoid and displays stem-like anatomy, producing paired traces into each cupule stalk. We speculate that the cupules can be related to other corystosperm organs from Antarctica, particularly the pollen-organ Pteruchus fremouwensis, based on similar secretory cavities. These specimens further support the interpretation of corystosperm reproductive structures as branching systems. In addition to aiding in the assessment of homologies among the Mesozoic pteridosperms, these new specimens may provide critical information on the placement of the corystosperms in seed plant evolution.

Key words: anatomy, Antarctica, Corystospermales, pteridosperms, Triassic, Umkomasia