Rosaceae

The family Rosaceae consists of about one hundred genera and three thousand species. It is distributed throughout the world, being especially common in North America, Europe, and Asia. Many members of the family are woody shrubs or trees. Others are perennial herbs: the stems die back at the end of each season and the root lives on to produce new stems in following seasons. The flowers of Rosaceae are distinctive because of the presence of a hypanthium, a cup-shaped structure forming the base of the flower. The sepals , petals, and stamens are attached to the edge of the hypanthium, while the pistil or pistils (which develop into the fruit or fruits) sit in the bottom of it.

One of the most conspicuous characteristics of Rosaceae is the variety of fruits produced by its species. Many Rosaceae have achenes and follicles, both of which are nonfleshy. Achenes contain one seed and have a hard fruit wall that does not split open at maturity, whereas follicles contain more than one seed and split open at maturity. Most fleshy fruits of Rosaceae are either drupes or pomes. A drupe (or stone fruit) contains one seed; the inner part of the fruit wall (the pit) is hard, and the outer fruit wall is usually fleshy. Peaches, plums, and cherries are examples of fleshy drupes, while almonds are nonfleshy. The fruits of raspberries and blackberries are clusters of many very small drupes. Pomes such as apples and pears are unusual fruits because the fleshy part does not develop from the pistil but from the hypanthium. The mature pistil containing the seeds is enclosed by the fleshy hypanthium. The fleshy part of the strawberry fruit is also not made from the pistil but from the base of the flower, which has expanded and become fleshy (accessory tissue). The fruits are achenes that are attached to the outside of the fleshy structure.

Rosaceae is very important economically. Many members of the family are important as ornamentals because of their foliage or flowers. Others are important components of diets in countries throughout the world because of

the fiber, phytochemicals, and vitamins they contain. Much of the fresh fruit eaten by people in temperate regions (apples, pears, strawberries, and cherries, for example) are members of family Rosaceae. Some members of Rosaceae are large enough to be sources of wood. The wood of wild black cherry (Prunus serotina; the largest species of Rosaceae) is a desirable furniture wood, and the wood of pear is used to make musical instruments such as recorders.

see also Economic Importance of Plants; Fruits; Horticulture.

David R. Morgan

Bibliography

Bailey, L. H. Manual of Cultivated Plants. New York: Macmillan, 1951.

Heywood, V. H., ed. Flowering Plants of the World. New York: Oxford University Press, 1993.

Simpson, B. B., and M. C. Ogorzaly. Economic Botany: Plants in Our World, 2nd ed. New York: McGraw-Hill, 1995.

Rosaceae A large and heterogeneous family of dicotyledonous (see DICOTYLEDON) trees, shrubs, and herbs that have alternate, stipulate leaves, and regular flowers, usually with inferior or partly inferior ovaries, or with the sometimes free carpels in a receptacular (see RECEPTACLE) cup. There are usually 4 or 5 free sepals and petals, and numerous stamens. Fruits are very varied. They may be achenes, drupes, follicles, or pomes (as in Malus). Many are cultivated for their edible fruits (e.g. Pyrus, Malus, Prunus, Rubus, and Fragaria), or for their flowers. In modern classifications, some 107 genera, with 3100 species are recognized, mostly in temperate zones, but cosmopolitan overall.