Ginkgoales: Some problems of systematics and phylogeny

The rudimentary outgrowths in fixed positions on the collars of Nagrenia samylinae Nosova (plant closely related to Ginkgo biloba L.) and similar rudiments in extant Ginkgo suggest that the collar of Ginkgo was initially a bilateral structure with directional growth, which bore ovule on its abaxial side. The collar of Ginkgo is interpreted as a vestigial organ. In the light of the data obtained, the origin and phylogeny of Ginkgoales are discussed; the most probable ancestors of Ginkgoales are Umkomasiales (Corystospermales) and allied plants. Thus, the new data confirm the interpretation of the collar of Ginkgo proposed by Meyen (1984) and are consistent with his hypothesis of the origin of Ginkgoales.