Ovule-bearing reproductive organs of the glossopterid seed ferns from the Late Permian of the Beardmore Glacier region, Antarctica

Abstract

The Glossopteridales are an extinct group of seed ferns that dominated Gondwana during the Permian. The strap-shaped leaves of Glossopteris are widespread and provided early evidence of continental drift, but reproductive organs of this group have remained enigmatic since they were first described in the 1950s. Based on compression- impression fossils, there are at least two basic types of ovulate (seed-bearing) organs. In one form, numerous ovules are borne on the surface of a leaf-like megasporophyll (e.g., Plumsteadia, Dictyopteridium), while the second type consists of stalked, apparently uniovulate cupules borne on a branching system (e.g., Lidgettonia). More than 30 genera of seed- bearing organs have been described, many based on compressions or, more commonly, impression fossils, in which it is often impossible to discern the three-dimensional morphology or attachment of these structures. Both morphological types have now been found in permineralized peat from Skaar Ridge, central Transantarctic Mountains (CTM), and provide some of the first anatomical detail of the diversity of reproductive organs of Glossopteris. The multiovulate organ is small (6 mm wide), with ovules borne on the upper (adaxial) surface; the uniovulate structure consists of four stalked cupules, each containing a single ovule about 2 mm long. These two forms provide important information about the diversity of the glossopterids and their status as a natural group of seed plants.