On a new medullosan pollen organ from the Pennsylvanian of North America

Interpreting the reproductive biology of fossil plants has contributed significantly to our understanding of plant evolution. Especially important are studies that have focused on structurally preserved reproductive organs that contain pollen or spores. Among Carboniferous pteridosperms, the medullosans are interpreted as a highly diverse group based on a large number of pollen organs and ovules. Here we report a permineralized pollen organ of Pennsylvanian age (Breathitt Formation) from eastern Kentucky, USA. The synangium is slightly more than a centimeter long and approximately 2.5 mm in diameter, and composed of 10-12 thin-walled, elongate sporangia. Vascular bundles occur in the periphery of the ground tissue. Pollen grains are of the Monoletes-type and up to 195 μm long. When compared with other Monoletes-producing pollen organs, the Lewis Creek synangium is most similar to the impression/compression morphotype Aulacotheca. Based on the co-occurrence of vegetative and reproductive organs, we suggest that this pollen organ was borne on Medullosa anglica.