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Gymnosperms are one of the two major groups of plants that produce seeds; the other is the angiosperms. Gymnosperm literally means "naked seed," which refers to the development of seeds exposed on a flat structure, that is, not within an ovary as in the angiosperms.

Gymnosperms became common about 290 million years ago and although many of the earlier types are now extinct, four kinds remain alive: the conifers, cycads, gnetophytes, and ginkgo, the maidenhair tree. Conifers are the most familiar, widespread, and abundant of the gymnosperms. Most conifers have needle- or scale-like leaves that persist for more than one year, that is, are evergreen. The conifers include species of pine, spruce, fir, hemlock, cedar, juniper, and redwood. The latter is the largest plant, exceeding 328 ft (100 m) in height. Conifers dominate boreal forests of high latitudes and mature forests of high altitudes, and are extremely valuable commercially. Their wood is used to make houses, furniture, and paper products. Resin, an organic secretion of conifers, has various uses ranging from turpentine for thinning paint, to resin blocks for making violin bows sticky. Some pines produce edible nuts and juniper berries are used to give gin its distinctive taste.

The other kinds of living gymnosperms are much less abundant, more geographically restricted, and less valuable than conifers. These gymnosperms are highly diverse, however, and sometimes quite strange. The cycads, or Sago palms, look like palms but are not (palms are flowering plants). Cycads are unusual among plants in that each individual is either a male or female, as in most animals. Most seed-producing plants are bisexual. The gnetophytes as a group are the oddest of the gymnosperms, and the oddest of these is Welwitschia. This species lives in sandy deserts of southwestern Africa. Welwitschia has a saddle-like, central core that produces only two leaves during the life of the plant. These grow continuously, frequently splitting along their length to give a mop-headed appearance.

Lastly, the ginkgo or maidenhair tree (Ginkgo biloba) is the only living species of a group that was most common about 170 millon years ago. The ginkgo has distinctive, fan-shaped leaves that are sometimes cleft in the middle and, unlike the leaves of most gymnosperms, fall each autumn. Ginkgo trees also are either male or female. Because of its unusual and attractive leaves, this species is widely planted as an ornamental. Curiously, the ginkgo appears to be extinct in the wild, only having survived through cultivation by Buddhist monks in China.

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Science EncyclopediaScience & Philosophy: Glucagon to Habitat