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 shed their foliage each year. Some nontropical broadleaf trees, however, such as certain magnolias and hollies, are evergreen—that is, they retain foliage throughout the year. In warmer parts of the United States and in the tropics, most broadleaf trees are evergreen. Broadleaf trees include virtually all of the familiar trees and shrubs that are known to flower, such as the elm, chestnut, alder, birch, and willow, as well as tropical species such as teak and mahogany.
The most recognizable trees in the monocot angiosperm class are the palm trees. There are about 2500 species of palms, including the coconut palm and date palm. Most palms lack branches and instead have enormous compound leaves (leaves composed of leaflets arranged along a central stem). Lily trees are another member of the monocot class. These trees are closely related to the familiar garden lily and include yucca trees such as the odd-looking Joshua tree, which is found in the deserts of the southwestern United States.
B. Gymnosperms
The needle-leaf trees, or conifers, include such trees as the pine, spruce, fir, yew, redwood, and cypress. The seeds of these gymnosperms are usually produced in cones at the base of protective scales. As their name implies, needle-leaf trees have slender needle-shaped leaves. Because of their small surface area and structure, needle leaves are not seriously injured by very low temperatures or by severe droughts. For this reason, the forests of cold far northern latitudes and high-altitude arid regions consist mostly of needle-leaf trees. Most needle-leaf trees are evergreens and retain most of their foliage throughout the year. Deciduous members of the group include the bald cypress and the larch.
The ginkgo, or maidenhair tree, is the sole living survivor of the ancient division of ginkgo gymnosperms. The ginkgo was abundant in the Mesozoic era (about 240 million to 65 million years ago). Virtually unchanged since that time, this tree is recognized by its fan-shaped leaves and the forking vein patterns on its leaves. A deciduous tree, the ginkgo grows slowly but may attain heights of more than 30 m (more than 98 ft). Ginkgos are native to Asia, where they have been preserved as sacred trees in Chinese temples since antiquity, but they are also cultivated in Europe and the United States.
Cycads are palmlike gymnosperms found mainly in tropical and subtropical regions of Africa, Asia, and Central America. Cycads are evergreen and may grow to heights of more than 18 m (more than 59 ft). They first appeared 285 million years ago and were the dominant plant type during the age of the dinosaurs, which roughly paralleled the Mesozoic era. Because the cycad is a popular ornamental tree, most cycad species are in danger of extinction because so many of them have been collected from the wild.
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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 shed their foliage each year. Some nontropical broadleaf trees, however, such as certain magnolias and hollies, are evergreen—that is, they retain foliage throughout the year. In warmer parts of the United States and in the tropics, most broadleaf trees are evergreen. Broadleaf trees include virtually all of the familiar trees and shrubs that are known to flower, such as the elm, chestnut, alder, birch, and willow, as well as tropical species such as teak and mahogany.
The most recognizable trees in the monocot angiosperm class are the palm trees. There are about 2500 species of palms, including the coconut palm and date palm. Most palms lack branches and instead have enormous compound leaves (leaves composed of leaflets arranged along a central stem). Lily trees are another member of the monocot class. These trees are closely related to the familiar garden lily and include yucca trees such as the odd-looking Joshua tree, which is found in the deserts of the southwestern United States.
B. Gymnosperms
The needle-leaf trees, or conifers, include such trees as the pine, spruce, fir, yew, redwood, and cypress. The seeds of these gymnosperms are usually produced in cones at the base of protective scales. As their name implies, needle-leaf trees have slender needle-shaped leaves. Because of their small surface area and structure, needle leaves are not seriously injured by very low temperatures or by severe droughts. For this reason, the forests of cold far northern latitudes and high-altitude arid regions consist mostly of needle-leaf trees. Most needle-leaf trees are evergreens and retain most of their foliage throughout the year. Deciduous members of the group include the bald cypress and the larch.
The ginkgo, or maidenhair tree, is the sole living survivor of the ancient division of ginkgo gymnosperms. The ginkgo was abundant in the Mesozoic era (about 240 million to 65 million years ago). Virtually unchanged since that time, this tree is recognized by its fan-shaped leaves and the forking vein patterns on its leaves. A deciduous tree, the ginkgo grows slowly but may attain heights of more than 30 m (more than 98 ft). Ginkgos are native to Asia, where they have been preserved as sacred trees in Chinese temples since antiquity, but they are also cultivated in Europe and the United States.
Cycads are palmlike gymnosperms found mainly in tropical and subtropical regions of Africa, Asia, and Central America. Cycads are evergreen and may grow to heights of more than 18 m (more than 59 ft). They first appeared 285 million years ago and were the dominant plant type during the age of the dinosaurs, which roughly paralleled the Mesozoic era. Because the cycad is a popular ornamental tree, most cycad species are in danger of extinction because so many of them have been collected from the wild.
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