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Seed plants all of which produce woody stems. Like the Cycads and Ginkgoes are well represented in the fossil record with members dating from the upper Carboniferous. Unlike these other "gymnosperm" phyla, however, the conifers are important today economically and ecologically. The group consists of around 550 species arranged in seven famies. All seven families can be dated back to the Mezazoic.
Vegetative Characteristics: All members produce abundant secondary xylem and grow as either trees or shrubs. Trachiary elements in the xylem include only tracheids, and the sieve elements of the phloem include only sieve cells. Leaves are macrophylls but take the form of needles or scales for most species.
Reproductive Characteristics: Dioecious or monecious plants. Pollen (microgametophyes) is produced in microsporangiate stobili (pollen cones) made up of sporophylls where the pollen sacs (microsporangia) are borne on the lower surface. All species are wind-pollinated. Sperm are not flagellated and are carried directly to the egg by means of a pollen tube. With the exception of the Taxaceae, ovules are borne in complex or secondarily reduced megasporangiate stobili (seed cones) consisting of seed scales bearing ovules. These are subtended by a sterile bract. Together the seed-scale with its sterile bract is termed a seed-scale complex. These are aranged around the central axis of the ovulate cone.