Laurel Family (Lauraceae)
Laurel Family (Lauraceae)
Characteristics of the Lauraceae
The laurels are a family of flowering plants known to botanists as the Lauraceae. Lauraceae contains about 45 genera and 2,000 species, and is the most diverse family in the order Laurales. Most species grow in the tropical forests of Southeast Asia and Central and South America.
The best known species is Laurus nobilis, a Mediterranean shrub used by the ancient Greeks to decorate the head of victors in the Pythian games, which led to modern phrases such as “poet laureate” and “Nobel laureate.” Other well-known species include avocado, California laurel, sassafras, and cinnamon trees. American gardeners often refer to Kalmia latifolia as “mountain laurel,” and to Rhododendron maximum as “great laurel,” despite the fact that both of these shrubs are in the Ericaceae family, and are unrelated to the “true” laurels of the Lauraceae.
Characteristics of the Lauraceae
The flowers of most species in this family are small, yellow, and aromatic. Some species have bisexual flowers containing both male and female organs. Others have unisexual flowers, with each one having either male or female organs. Some species are polygamous, in that individuals have some flowers which are bisexual, and others that are unisexual.
The flowers of most species have six sepals, arranged in two cycles. (Sepals are the outermost whorl of a flower, typically leaf like in appearance.) The stamens, or male organs, of laurel flowers occur in three or four cycles, with three stamens in each. The flowers usually have a single pistil, or female organ, which contains a single ovule that develops into a seed after fertilization. The fruit of most species is aromatic, and is classified as a drupe, in that is has a fleshy outer layer and a hard inner layer with a single seed.
The leaves, stems, and roots of most species in the laurel family are aromatic. The leaves are typically alternate, rather than opposite, to one another on the stem. The leaves are simple in that they consist of a single blade. The California laurel (Umbellularia californica ) and most tropical species in the Lauraceae have persistent leaves, which remain attached to the plant after they are no longer functional. Other species such as sassafras (Sassafras albidum ) and spice bush (Lindera benzoin ) have seasonally deciduous leaves, which fall off in the autumn, after they become nonfunctional.
Important species
The avocado (Persea americana), also known as the alligator pear, is one of the best known and most economically important species of the laurel family. Avocado is native to tropical regions of the Caribbean, Mexico, and South America. Many different races and varieties are cultivated in southern France, South Africa, Mexico, California, and Florida for their green edible fruits, which are eaten raw or used to make guacamole, a staple of Mexican cuisine.
The avocado fruit can be green or brown, depending on the variety, and is rich in oil. The avocado fruit is a drupe with a single large seed in the center. The early Spanish explorers, who observed avocado cultivation by the Aztecs, thought that the fruit resembled a testicle, and that a man could increase his sexual potency by eating avocados. (This belief was based on the “doctrine of signatures,” which holds that a plant part that resembles a bodily organ would affect the function of that organ. We now know that the doctrine of signatures has no scientific basis.)
The California laurel (Umbellularia californica) is a woody plant that grows from southern California to southern Oregon, and is the only species of this family native to the western United States. It has evergreen, aromatic, elliptical leaves. Under optimal conditions, it grows as a tree and reaches 150 feet (46 m) or so in height, and is shrublike in appearance. Its wood is fine textured, and is sometimes used to manufacture veneer, furniture, and wooden novelties.
KEY TERMS
Bisexual —Flowers that have functional male and female organs.
Drupe —A fruit with a fleshy outer layer and a hard inner layer that encloses a single seed. A cherry is a typical example.
Pistil —Female reproductive organ of a flower, which contains ovules that develop into seeds after fertilization by pollen.
Polygamous —Plants that have some unisexual and some bisexual flowers.
Sepal —External whorl of a flower that 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.
There are three species in the genus Sassafras. One is from Taiwan, another from China, and one (Sassafras albidum) is a tree native to the eastern United States. Foresters classify the American sassafras as intolerant because it does not grow well under a closed forest canopy. Indeed, the American sassafras commonly grows in open fields and at the edge of forests. Its leaves are variable in shape, and can be elliptical, two-, or three-lobed. The leaves turn a characteristic red in the autumn. Leaves, roots, and twigs are all highly aromatic. Some biologists have suggested that Sassafras leaves are allelopathic, in that they chemically inhibit the growth of nearby plants, thus reducing competition. Sassafras tea is made by removing and boiling the bark from the roots. Sassafras oil is used in the manufacture of certain aromatic bath oils.
All species in the Cinnamomum genus are aromatic, and most are native to Southeast Asia. Cinnamon is a well-known spice which comes from Cinnamomum zeylanicum, a tree native to Sri Lanka but now cultivated throughout Asia, the Caribbean, and South America. Commercial cinnamon comes from the bark of young twigs, which is stripped off, dried in the sun, and later powdered or used whole.
Another species in this genus, Cinnamomum camphora, is the source of camphor. This tree is native to Southeast Asia. Camphor is an aromatic compound derived from the bark and wood of the camphor tree and is used as a medicine to relieve gas pains in the digestive tract, in ointments, and as an insect repellent.
Resources
BOOKS
The American Horticultural Society. The American
Horticultural Society Encyclopedia of Plants and Flowers. New York: DK Publishing, 2002. Audubon Society and staff. Familiar Trees of North
America: Eastern Region. New York: Knopf, 1987. Heywood, V.H. Flowering Plants of the World. Oxford:
Oxford University Press, 1993.
OTHER
Texas A & M University, Center for the Study of Digital Libraries. “Lauraceae—Laurel Family” <http://www.csdl.tamu.edu/FLORA/301Manhart/Dicots/Magnol/Lau/Lau.html> (accessed December 2, 2006).
Peter A. Ensminger