Spermatophyta
Spermatophyta (also Spermatopsida) is the seed-bearing plant taxon in the Kingdom Plantae. Spermatophytes are part of the larger clade of embryophytes, or land plants, the latter also including the non-seed bearing plant groups: ferns, mosses, liverworts, and hornworts that reproduce by means of spores.
Seed-bearing plants were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetae, cycads, ginkgo, and conifers. Angiosperms are now thought to have evolved from a gymnosperm ancestor, which would make the gymnosperm taxon paraphyletic. Modern cladistics attempts to define taxa that are monophyletic, traceable to a common ancestor and inclusive therefore of all descendants of that common ancestor. Although not a monophyletic taxon, gymnosperm is still widely used to distinguish the four taxa of non-flowering, seed-bearing plants from the angiosperms.
A traditional classification grouped all the seed plants together as follows:
In addition to the taxa listed above, the fossil record contains evidence of many extinct taxa of seed plants. The so-called "seed ferns" (Pteridospermae) were one of the earliest successful groups of land plants, and forests dominated by seed ferns were prevalent in the late Paleozoic. Glossopteris was the most prominent tree genus in the ancient southern supercontinent of Gondwana during the Permian epoch. By the Triassic period, seed ferns had declined in importance, and gymnosperms were predominant until the Cretaceous, when the Angiosperms became predominant.
A more modern classification splits these groups into separate divisions (sometimes under the Superdivision Spermatophyta):
Modern phylogeny seems to indicate that the monocots and dicots are not sibling taxa, but that the monocots are descended from a primitive dicot ancestor, which would make the dicots a paraphyletic group. Some botanists contend that since Magnoliopsida is paraphyletic it should be split into at least two other classes: Palaeodicots, or primitive dicots (including Magnolia) and the Eudicots. Under this scheme, the palaeodicots are still a paraphyletic taxon, which includes roughly a half-dozen monophyletic clades. Many modern classification systems, including that of the Angiosperm Phylogeny Group, recognize the monocots and eudicots as clades, and divide the palaeodicots into several monophyletic groups.
