D. Ginkgo, Pentoxylon, Czechanowskia and Gnetophytes 1. Ginkgophytes are another group with an extensive fossil record from the Permina to recent that today are represented by a single monotypic species. Both modern day and fossil ginkgos have a great deal of variability in leaf morphology, even in a single tree, adding to the confusion associated with this group. Ginkgo is dioecious, with some plants producing lax pollen catkins and other ovules paired on stalks. The ovulate structure of Ginkgo is interpreted as a reduced compound cone.
Pollen is monosulcate and looks a lot like cycad pollen.
Pollen organs have pollen similar to cycad, ginkgo and bennettitalean pollen. This is a Mesozoic group of plants that have narrow, elongate forking needle-like leaves and ovulate reproductive structures that look like bivalvate clam shells that contain several ovules each. The ovulate structures have been compared to angiosperm carpels but the group remains poorly known. Although these three plants are quite distinct from one another in plant habit and distribution they share similar enough vegetative and especially reproductive structures to be considered together taxonomically by most authors. They are all characterized by eusteles surrounded by pycnoxylic wood that may have vessels similar to those of dicots, whorled leaf and bract organization, and dioecious plant habit.