Kids Research Express

Types of Trees There are two general types of trees, angiosperms and gymnosperms . Angiosperms are flowering plants in which the ovule, or seed, is encased in a protective ovary. With about 235,000 species, the angiosperm division is the largest and most diverse plant group. It is divided into dicots , plants with two cotyledons (seed leaf structures), that include the familiar broadleaf trees such as maple and oak ; and the monocots , plants with one cotyledon that include the palms and lily trees. Unlike angiosperms, gymnosperms (Greek for “naked seed”) do not bear flowers. Their seeds lie exposed in structures such as cones or fleshy cups called arils. The group includes about 500 tree species—including three major types, needle-leaf trees (or conifers ), ginkgos , and cycads . A. Angiosperms As angiosperms, all dicots produce flowers, and their seeds are always enclosed in a protective covering. In temperate regions, most of these broadleaf trees are deciduous, meaning that they

Importance of trees Perhaps the most important ecological function of trees is protecting the land against erosion , the wearing away of topsoil due to wind and water. The trunks and branches of trees provide protection from the wind, and tree roots help solidify soil in times of heavy rain. In addition, trees and forests store water reserves that act as buffers for the ecosystem during periods of drought. In many areas the removal of forests has resulted in costly floods and subsequent droughts. Trees and forests also provide habitat, protection, and food for many plant and animal species. In addition, they play an important role in global climate and atmosphere regulation—the leaves of trees absorb carbon dioxide in the air and produce oxygen that is necessary for life. Trees have many economic uses. Lumber from trees is the most widely used material in the building of homes and other structures. Many trees yield edible fruits and nuts such as oranges, grapefruits, apples, avocados,

Tree, woody plant with a distinct main stem , or trunk. At maturity, trees are usually the tallest of plants, and their height and single main stem differentiate them from shrubs , which are shorter and have many stems. Trees are perennials, plants that live for at least three years. Some species of tree only grow to 4 m (13 ft) in height, but the tallest species may reach heights of more than 112 m (more than 367 ft). The General Sherman Tree, a giant sequoia in California’s Sequoia National Park, has a height of 84 m (275 ft) and a diameter of 11 m (37 ft). The largest trees, however, are not necessarily the oldest. For example, the bristlecone pine grows to a height of only about 9 m (about 30 ft), but one specimen has been dated as at least 4,600 years old. Trees grow throughout the world, from the extreme cold regions near the Arctic and the Antarctic to the hot tropical regions around the equator. They grow in both good and poor soil, in deserts and swamps, along shores, and at

Palm (plant), common name for a family of woody flowering plants widespread in the tropics. They are of great economic importance because of the food, fiber, and oil they provide, and because of their ornamental uses. The family is the only member of its order and contains about 2,600 species, making it the fourth largest among the monocots , after the grasses , lilies , and orchids . Palms have a characteristic growth form: a single, unbranched trunk topped with a tuft of fanlike or featherlike leaves. The flowers are borne in axillary clusters (inflorescences), and a large, interwoven mass of roots occurs at the trunk base. The trunks of palms, like those of other monocots, have no secondary growth; thus, the diameter of the trunk does not increase with the age of the tree, as in dicots . The growing tip of the trunk instead is built up into a large mass in the seedling stage, and maintains that broad width as the trunk matures. Bundles of vascular tissue are scattered throughout the

Species and Speciation, basic concepts in the classification of organisms. In simple terms, a single species is a distinct kind of organism, with a characteristic shape, size, behavior, and habitat that remains constant from year to year. A biological species is defined as a group of natural populations that mate and produce offspring with one another, but do not breed with other populations. This definition includes genealogical relationships as well as physical properties, and emphasizes that species evolve independently of one another. See Evolution . THE NATURE OF SPECIES Other conceptions of species exist, the oldest of which is the typological-species concept that originated with Plato and Aristotle. According to this concept, a species represents some ideal form, of which individual variation is merely the imperfect expression. The morphological-species definition, on the other hand, is purely observational: a group of individuals that resemble one another and are separated f

Biology, the science of life. The term was introduced in Germany in 1800 and popularized by the French naturalist Jean-Baptiste de Lamarck as a means of encompassing the growing number of disciplines involved with the study of living forms. The unifying concept of biology received its greatest stimulus from the English zoologist Thomas Henry Huxley, who was also an important educator. Huxley insisted that the conventional segregation of zoology and botany was intellectually meaningless and that all living things should be studied in an integrated way. Huxley’s approach to the study of biology is even more cogent today, because scientists now realize that many lower organisms are neither plants nor animals (see Prokaryote ; Protista ). The limits of the science, however, have always been difficult to determine, and as the scope of biology has shifted over the years, its subject areas have been changed and reorganized. Today biology is subdivided into hierarchies based on the molecule, t

Stem, portion of vascular plants that commonly bears leaves and buds. It usually is aerial, upright, and elongate, but may be highly modified in structure. Subterranean stems include the rhizomes of the iris and the runners of the strawberry; the potato is a portion of an underground stem. Some plants, such as the century plant, have very short stems that bear a dense cluster of leaves. Those points on the stem at which leaves or buds arise are called nodes, and the regions of the stem between the nodes are known as internodes. The chief functions of stems are the production and support of leaves and reproductive structures, conduction of water and nutrients and food storage. In some plants, such as cactus, stems also have the specialized functions of storing water and manufacturing food. Conducting tissues within plant stems are arranged in columns called vascular bundles. These bundles are composed of xylem , which conducts water up the stem, and of phloem , which transports sugars p