XVI International Botanical Congess

The Ginkgoales were gymnosperms that essentially had seed cones in most Jurassic and Cretaceous representatives. This organization is not the condition found in the extant Ginkgo biloba. In this paper we describe additional material of the ginkgoalean seed cone Karkenia incurva Archang. with cuticle in a better stage of preservation (Lower Cretaceous, Patagonia).The seed cone is dense with ab. 100 overlapping, irregularly disposed ovules, attached to the central axis. Ovules anathropous, ovoid with the micropylar end towards the central axis. The following cuticles of the ovules were recovered: the outer epidermis of the integument differentiated into two zones, the nucellus and the megaspore membrane. Ultrastructural features of this membrane compared with those seen in G. biloba suggest the ovules of K. incurva were at the latest stage of development at time of fossilization. Karkenia is compared with other members of the group. Relationship among Ginkgoales are discussed.