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Palms are mostly unbranched shrubs or trees, and are the main tree family within the monocotyleons. Typically the solitary erect stem is crowned by large, persistent leaves that are sheathing at the base. The leaves of Raphia fainifera are the largest of any flowering plant, sometimes reaching more than 65 ft (20 m). Palm leaves are occasionally simple, but usually they are dissected into a fan shape (palmate) or feather shape with many distinct segments that run perpendicular to the main axis of the leaf (pinnately compound). The stem may be very short, so as to appear virtually absent, to 164 ft (50 m) in height. Not all palms have single stems or trunks. Some palms have clustered stems that arise from buds at the base of the initial stem, for example, Phoenix. A few unusual species, such as Chrysalidocarpus madagascariensis, have some individuals with solitary straight trunks and other individuals with clustered trunks. Some palms are climbing vines, such as the rattans.

The trunk of palms is very different from the trunk of the conifer or dicotyledonous trees that dominate temperate regions. Conifers, such as pines, spruces, and hemlocks, and dicotyledenous trees, such as maples, oaks, and elms, increase the width of their trunk as they grow by a process called secondary growth. During this process, a ring of specialized cells under the bark of the tree produces new wood toward the center of the tree and other kinds of specialized conducting tissues toward the bark side. Secondary growth is absent in palms. Instead, when a seed germinates, the seedling first grows into an inverted cone whose width matches the full width of the trunk to be grown. Only after this radial growth is completed does the seedling begin to grow vertically, maintaining its width. If a nail is driven into a conifer or dicotylenous tree's trunk, the tree will grow around it eventually completely embedding the nail within the trunk. A nail driven into the trunk of a palm will remain where driven and not become embedded within the trunk.

Palm flowers are occasionally bisexual, but usually they are unisexual. When unisexual, the flowers of each sex may be on the same plant or, as in humans, only one sex is found per individual. The flowers are small and are generally borne on large, many-branched stems (inflorescences) that are located within the crown or just below it. Flower parts are normally in threes. The pollination biology of palms is not well studied, nevertheless, both wind and insect pollination are common in the family.

Palm fruits are berries, which are simple, fleshy fruits that contain one or more seeds, or drupes, which are simple, fleshy fruits that contain one seed that is surrounded by a bony pit, a stone fruit. The largest fruit in the world comes from the double coconut palm (Lodoicea sechellarum) and weighs up to 40 lb (18.2 kg).

Additional topics

Science EncyclopediaScience & Philosophy: Overdamped to PeatPalms - Distribution, Structure, Food, Oil, Fiber, Ornamentals - Economic uses