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Oleaceae

Oleaceae A family of trees or shrubs that have opposite, exstipulate leaves and usually tetramerous flowers with 2 stamens attached to the corolla tube. The ovary is superior and 2-celled. Besides Olea, Fraxinus (ash) is an important timber tree, with reduced flowers that normally lack a perianth. There are some 24 genera, with 900 species, widely distributed but centred on Asia.

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Olive Family (Oleaceae)

Olive Family (Oleaceae)

Characteristics of the olive family

Important species

Resources

The olive family is a family of flowering plants known to botanists as the Oleaceae. The Oleaceae have about 25 genera and over 500 species. Most species are native to temperate and tropical regions of the Northern Hemisphere. The best known trees of this family are olive and ash, while the most familiar shrubs are privet, lilac, and golden bell, all popular ornamental plants.

Characteristics of the olive family

The flowers of most species have radial symmetry, in that any longitudinal section through the center of the flower would divide it into two identical halves. The flowers of some species are bisexual, in which both male and female organs are present. The flowers of other species are unisexual, in that they have male organs or female organs, but not both. The flowers of most species have four sepals (the typically green, leaf-like parts which constitute the outermost whorl of flowers) and four petals (the typically pigmented, leaf-like parts which are interior to the sepals, but exterior to the sexual organs). Most species have flowers with two stamens (male organs) and one pistil (female organ). The pistils of most species contain four ovules, which develop into seeds after fertilization.

The fruit of some species, such as the ash, is a samara, or a dry, one-seeded fruit which is indehiscent (lacks a suture), and has wing-like structures to facilitate dispersal by the wind. The fruit of other species, such as the olive, is a drupe, or a fruit with a fleshy outer layer and a hard inner layer containing one seed. The fruit of other species is a berry, a fruit that is fleshy throughout and has one or more seeds.

Some species, such as ash, have seasonally deciduous leaves, which fall off in the autumn after they become non-functional. Other species, such as olive, have persistent leaves, in that there are always some leaves attached to the tree, even when they are no longer functional. In most species in this family, the leaves arise opposite to one another on the stem. The leaves of some species, such as lilac and golden bell, are simple in that they consist of a single blade. The leaves of other species, such as ashes, are compound, and are composed of many separate leaflets.

Important species

The olive tree (Olea europea) is the best known and most economically important species in this family. This Mediterranean native produces olives and olive oil. Italy and Greece are the major producers of these products. However, olive trees are now cultivated throughout the world, including southern California, South America, and Australia. Olive trees cannot withstand cold winter temperatures.

Olive trees probably originated in Greece, and were later introduced to Italy and elsewhere in the Mediterranean region. Olive oil was well known to the peoples of the Middle East several millennia ago. The Old Testament of the Bible mentions the use of olive oil as an ointment, food, and for burning in lamps. Olive trees are especially well-known in Italy and Greece, where olives and olive oil have been used in the cuisine for thousands of years.

The olive tree has persistent leaves, blooms in the spring, and produces mature fruits in the late autumn or winter. The unripe fruits are green and bitter, while ripe fruits are purple to black in color. The bitterness of the green, unripe fruits can be removed by soaking them in a solution which is alkaline (high pH) or is saturated with salt. Once the bitterness has been removed, green olives are typically pickled in a salt solution for later eating.

Olive oil is made from the ripe, purple fruits. Olive oil has a relatively high percentage of unsaturated fatty acids, and is purportedly healthier than many other vegetable oils. It consists of about 80% oleic acid and 10% palmitic acid. Extra virgin olive oil is considered the best, and is prepared by extraction without the use of chemical solvents. Pure olive oil is extracted with the use of chemical solvents, and this process removes some of the color and flavor that is so characteristic of extra virgin olive oil.

Olive trees are slow-growing, but can live one thousand years or more. The trunks of mature trees have a very characteristic, gnarled appearance. Olive trees are not used as timber, but the wood has a fine grain and has been traditionally used to make hand-carved implements.

There are about 65 trees and shrubs in the ash (Fraxinus ) genus. All species are native to the Northern Hemisphere, and about 18 are native to North America. The leaves of all ash species arise opposite to one another on the stem, and with one exception (Fraxinus anomala ), are pinnately compound, in that they consist of numerous small leaflets which arise from a central stalk.

The white ash (Fraxinus americana ) is the tallest and most important of the American ashes. It grows throughout the angiospermforests of eastern North America, and has a characteristic long, straight trunk and leaves which turn yellow or purple in the autumn. The wood of white ash is flexible and light, and is used to make baseball bats and furniture.

Lilac (Syringa vulgare ) is native to southeastern Europe, but is widely cultivated throughout the United States and much of southern Canada as an ornamental, flowering shrub. Lilac shrubs produce large, branched inflorescences, referred to as panicles, in early spring. The flowers are purple or white, and have a characteristic aroma. Lilac has escaped form cultivation and become naturalized in parts of temperate North America. This naturalized, European native is the state flower of New Hampshire.

Privet (Ligustrum vulgare ) is also a shrub native to Europe. It can take substantial abuse, and so has become the most widely planted hedge plant in the United States. Privet produces flowers in May, and blue-black berries in summer which are eaten by birds. Birds disperse the seeds within the berries, and have thereby naturalized privet through much of the United States.

Golden bell (Forsythia viridissima and several other species of Forsythia ) is a cultivated shrub which is native to China. Golden bell has twigs which are yellow-brown in color, and it produces brilliant,

KEY TERMS

Bisexual Flowers that have functional male and female organs.

Drupe A fruit which has a fleshy outer layer, and a hard inner layer which encloses a single seed. A cherry is a typical example.

Pistil The female reproductive organ of a flower, which contains ovules that develop into seeds after fertilization by pollen.

Sepal External whorl of a flower which is typically leaflike and green.

Stamen Male reproductive organ of a flower that produces pollen.

Unisexual Flowers that bear either male or female reproductive organs.

Unsaturated Containing multiple bonds between the carbon atoms in a chain. Unsaturated fatty acids contain at least one double bond between two carbon atoms.

yellow flowers in early spring. Like privet, it is a popular hedge plant.

Resources

BOOKS

Humphries, C.J., J.R. Press, and D.A. Sutton. Guide to Trees of Britain and Europe. London: Hamlyn Publishing Group, 2001.

Raven, Peter, R.F. Evert, and Susan Eichhorn. Biology of Plants, 7th ed. New York: Worth Publishers Inc., 2004.

Taylor, Judith M., and Kevin Starr. Olive in California: The History of an Immigrant Tree. Berkeley, CA: Ten Speed Press, 2000.

White, John, and David More. Illustrated Encyclopedia of Trees. Portland, OR: Timber Press, 2003.

Peter A. Ensminger

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"Olive Family (Oleaceae)." The Gale Encyclopedia of Science. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

"Olive Family (Oleaceae)." The Gale Encyclopedia of Science. . Encyclopedia.com. (April 27, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/olive-family-oleaceae-0

"Olive Family (Oleaceae)." The Gale Encyclopedia of Science. . Retrieved April 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/olive-family-oleaceae-0