Spermatophyte

The spermatophytes (from the Greek word "Σπερματόφυτα") (also known as phanerogams) comprise those plants that produce seeds. They are a subset of the embryophytes or land plants. The living spermatophytes form five groups:

• cycads, a subtropical and tropical group of plants with a large crown of compound leaves and a stout trunk,
• Ginkgo, a single living species of tree,
• conifers, cone-bearing trees and shrubs,
• gnetophytes, woody plants in the genera Gnetum, Welwitschia, and Ephedra, and
• angiosperms, the flowering plants, a large group including many familiar plants in a wide variety of habitats.

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 period. By the Triassic period, seed ferns had declined in ecological importance, and representatives of modern gymnosperm groups were abundant and dominant through the end of the Cretaceous, when angiosperms radiated. Another Late Paleozoic group of probable spermatophytes were the gigantopterids.

Evolution

A whole genome duplication event in the ancestor of seed plants occurred about 319 million years ago.^[1] This gave rise a series of changes that resulted in the evolution of seed plants.

Relationships and nomenclature

Seed-bearing plants were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms,^[2] in particular based on vessel elements. However, molecular studies (and some more recent morphological^[3] and fossil^[4] papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like:^[5][6][7]

However, the relationships between these groups should not be considered settled.^[2][9]

Other classifications group all the seed plants in a single division, with classes for our five groups:

• Division Spermatophyta
  • Cycadopsida, the cycads
  • Ginkgoopsida, the ginkgo
  • Pinopsida, the conifers, ("Coniferopsida")
  • Gnetopsida, the gnetophytes
  • Magnoliopsida, the flowering plants, or Angiospermopsida

A more modern classification ranks these groups as separate divisions (sometimes under the Superdivision Spermatophyta):

• Cycadophyta, the cycads
• Ginkgophyta, the ginkgo
• Pinophyta, the conifers
• Gnetophyta, the gnetophytes
• Magnoliophyta, the flowering plants

References