Gymnosperms
The gymnosperms are vascular non-flowering seed plants. They bear their seeds in scales that form a cone-shaped structure. They have true roots, stems, and leaves. Gymnosperms can grow up to 15 meters in height. There are about 700 living species of Gymnosperms. The Gymnosperms include the conifer, cycads, and ginkgoes.
Cycads
Common name for a phylum of slow-growing palmlike plants, and for its representative genus. Today only 11 genera and 150 species of cycads occur, but during the Age of the Dinosaurs, the Jurassic Period , some 200 million years ago, they were the dominant plant life. Cycads are primitive gymnosperms with motile sperm cells, producing exposed seeds in conelike clusters at the apex of the plants. They occur in tropical, subtropical, and warm temperate areas. Most are good-size plants of unbranched columnar stems with frondlike leaves clustered at the tip. The only species that occurs in the United States is found in the sandy woods of Florida. This and other species are a source of to make bread and other starchy foods. Cycads are evergreens with attractive foliage, and plants of all genera are cultivated for their horticultural value. They are grown out-of-doors in warm areas and as houseplants in colder regions. One species, the Sago Cycas, is a popular bonsai subject. Most cycads are in danger of extinction because of indiscriminate collectors.
Conifers
Common name for a group of plants that is characterized by seed-bearing cones and that includes about 550 of the 700 known species of plants . There are two orders of conifers. Conifers are known from fossils more than 290 million years old. Although more species of conifers once existed, they are still a widely distributed group and are one of the world's most important renewable resources. Fossils of the ancestors of the newly discovered trees exist, but scientists had believed that the group had become extinct 50 million years ago. Conifers, like flowering plants reproduce by means of seeds, which contain food tissue and an embryo that will grow into a plant. The seeds are borne on the scales of female cones rather than being surrounded by carpel tissue, and the pollen is produced in separate male cones rather than in anthers. Pollination in conifers is always dependent on wind currents to blow the abundant yellow pollen from the male cones to the female cones. Conifers usually have needle-shaped or scalelike leaves, and nearly all are evergreen. They typically have straight trunks with horizontal branches varying more or less regularly in length from bottom to top, so that the trees are conical in outline. They vary in size from shrubs to giant sequoias.
Ginkgoes
Genus of deciduous trees; the maidenhair tree is the only living representative of its family and order, although other plants of this order were abundant in the Mesozoic era. The ginkgo has been preserved as a sacred tree in Chinese temple gardens since ancient times. Botanists long believed that the species would have become extinct without this care, but wild ginkgos have been found in recent years in remote valleys of western China. Ginkgo trees grow 12 to 37 m tall. The ginkgo leaf is a fan-shaped structure with veins arising from the base and branching dichotomously throughout. The common name, maidenhair tree, is derived from the resemblance in venation between the ginkgo and the maidenhair fern. Larger branches of the ginkgo are covered with dwarf branches, called spurs, which grow slowly and bear leaves yearly. The seed, called the ginkgo nut, is roasted and esteemed as a delicacy in China and Japan.
The ginkgo is frequently planted in parks and ornamental gardens. The tree is also grown on the streets in large cities, where it flourishes in spite of air pollution, low sunlight, and other urban conditions. Horticultural varieties of ginkgo have been developed as a result of such extensive use
