Pinophyta(redirected from Coniferous trees)
Pinophyta(pī'nŏf`ətə), division of the plant kingdom consisting of those organisms commonly called gymnosperms. The gymnosperms, a group that includes the pine, have stems, roots and leaves, and vascular, or conducting, tissue (xylem and phloem). In these plants the ovules, or young seeds, are exposed to the air at the time of pollination, hence the term gymnosperm, meaning naked seed. Pollination is always by wind. Because the seed-bearing structures of many gymnosperms are organized into a cone, or strobilus, these plants have been called conifersconifer
[Lat.,=cone-bearing], tree or shrub of the order Coniferales, e.g., the pine, monkey-puzzle tree, cypress, and sequoia. Most conifers bear cones and most are evergreens, though a few, such as the larch, are deciduous.
..... Click the link for more information. ; because the leaves of many species are perennial, they have also been called evergreens.
The class Cycadopsida, or cycads, are only the small evolutionary vestige of a large and varied group of plants that flourished in late Paleozoic and Mesozoic time. The only order of living cycads, the Cycadales, is dioecious, i.e., male and female cones are borne on separate plants. Although cycads resemble the palms in form and usually have erect stems that reach 50 ft (15 m) in height, they have very little wood; rather, they are supported largely by a hard outer layer of the stem. They have large, fernlike leaves and produce seeds in terminal cones. In their reproduction, pollen grains, or microspores, are transported by wind to the female spore case, or megasporangium. Within the microspore wall, motile flagellated sperms are produced, unlike the nonmotile sperms of the higher gymnosperms.
The class Pinopsida is characterized by generally small, always simple leaves and by the active secondary growth of stem and root. Many members of this group flourished from Lower Carboniferous times to the Permian age. Plants of the order Pinales (conifers) occur in the Northern Hemisphere; a few species occur within the tropics at sea level. Conifers are the most numerous of living gymnosperms and form large and relatively pure forests. Common examples of conifers are the pines, firs, spruces, redwoods, cedars, junipers, hemlocks, and larches. The wood of conifers is used extensively for construction of all kinds. It has no vessels and thus differs from the wood of angiosperm trees. Although conifers are called softwoods and angiosperm trees hardwoods, the wood of some pines is much harder than that of some angiosperms. Most conifers are monoecious, i.e., the male and female cones occur on the same tree. The microspores, or pollen grains, are produced in such vast abundance that clouds of pollen, carried on the wind, have settled on ships far at sea. In plants of the order Taxales (yewsyew,
name for evergreen trees or shrubs of the genus Taxus, somewhat similar to hemlock but bearing red berrylike fruits instead of true cones. Of somber appearance, with dark green leaves, the yew since antiquity has been associated with death and funeral rites.
..... Click the link for more information. ) the seeds, produced individually on short shoots, are surrounded by a conspicuous, fleshy covering.
The class Ginkgoopsida contains the contains the ginkgoginkgo
or maidenhair tree,
tall, slender, picturesque deciduous tree (Ginkgo biloba) with fan-shaped leaves. The ginkgo is native to E China, where it was revered by Buddhist monks and planted near temples.
..... Click the link for more information. , Ginkgo biloba, the last surviving species of a once large and flourishing group of gymnosperms. The class Gnetopsida contains three genera in separate orders, all of great botanical and evolutionary interest. Gnetum is a tropical tree or shrub with broad leaves much like those of an angiosperm. Ephedra is a low shrub with scalelike leaves that grows in arid regions of western North America and in China; from it is produced the traditional Chinese herbal medicine ma huang and the drug ephedrineephedrine
, drug derived from plants of the genus Ephedra (see Pinophyta), most commonly used to prevent mild or moderate attacks of bronchial asthma. Unlike epinephrine, to which it is chemically similar, ephedrine is slow to take effect and of mild potency and long
..... Click the link for more information. . Welwitschia, a desert plant of SW Africa, typically has only two large, leathery leaves that persist for the life of the plant, which can be as long as 1,500 years.
One of the two divisions of the seed plants, comprising about 600 to 700 species extant on all continents except Antarctica. The most familiar and common representatives are the evergreen, cone-bearing trees of the Pinales. Because the ovules (young seeds) are exposed directly to the air at the time of pollination, the Pinophyta are commonly known as the gymnosperms, in contrast to the other division of flowering plants, the angiosperms (division Magnoliophyta), which have the ovules enclosed in an ovary. The division Pinophyta consists of three classes: Ginkgoopsida, Cycadopsida, and Pinopsida. See Magnoliophyta, Plant kingdom