In certain classifications, a division containing the gymnosperms (see Gymnospermae). It is divided into the following subdivisions: Cycadicae (cycadophytes), containing the orders Pteridospermales, Caytoniales, Bennettitales, and Cycadales; Pinicae (coniferophytes), containing the orders Ginkgoales, Cordaitales, Coniferales, and Taxales; and the Gneticae (gnetophytes), containing the orders Ephedrales, Welwitschiales, and the Gnetales. The Cycadicae are differentiated from the Pinicae on the basis that they have palmlike compound leaves, motile antherozoids, radially symmetrical seeds, and loose soft wood. The Pinicae in contrast have simple leaves, non-motile sperm nuclei (except in Ginkgo biloba), bilaterally symmetrical seeds, and denser wood. The Gneticae resemble the Pinicae in having simple leaves, nonmotile sperm, and flattened seeds. However they differ from both the Pinicae and Cycadicae in possessing ovules with two integuments, rather than one, the inner of which is elongated into a tubular micropyle, and in having compound microstrobili. |
