Herb to Know: Eucalyptus

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What do you associate with the word “eucalyptus”? If you say “cough drops”, you’re not alone. Many people know this lofty herb solely from the camphorous fragrance of several species whose essential oil is an ­ingredient of popular cold remedies. However, the genus Eucalyptus comprises more than 500 species and perhaps 200 varieties of evergreen trees and shrubs, and the familiar medicinal smell is just one in the spectrum of fragrances found in this aromatic genus.

Nearly all the species are native to Australia and Tasmania, where they occupy every habitat but desert, growing at every altitude from sea level to 6500 feet. A number have been introduced to India, Africa, Europe, southern China, the former Soviet Union, the Middle East, and North and South America.

Plants range in height from a few feet to 380 feet (E. regnans is the world’s tallest hardwood). All parts of the plant are aromatic. Fragrances include lemon, apple, honey, and peppermint, in addition to the familiar camphorous scent. The trunks are straight. The bark may be smooth or peeling, fibrous, or rough and fissured. Most species have leaves of two kinds. The juvenile leaves are rounded or heart-shaped in pairs on the stem; in some species, the stem appears to pierce a single leaf. Adult leaves are pendulous, usually alternate, lance- or sickle-shaped, bluish or gray-green, and smooth, shiny, tough, and leathery. A thick cuticle slows water loss during droughts.

The generic name Eucalyptus comes from the Greek for “well covered” and refers to the cap, or operculum, of fused sepals and petals that covers the flower bud and is later cast off as the bud expands. Flowers are showy puffs with numerous protruding stamens. Most are white, but some species and varieties have yellow, pink, or red flowers. They are usually borne in clusters.

The genus includes gums, often tall with smooth or peeling bark; ironbarks, with hard, rough, persistent bark; bloodwoods, with rough, scaly, and flaky bark; boxes, with rough and ­fibrous bark; peppermints, with finely fibrous bark (and a peppermint aroma); and stringybarks, with long-fibered bark. Mallees are shrubby, usually with several stems rising from a woody rootstock called a lignotuber; marlocks are another shorter kind. Some species are known by their aboriginal names—illyarrie, wandoo, moort, jarrah, mottlecah, coolibah. An all-purpose common name is eucalypt.

Most eucalypts in the United States are found in California. About seventy-six kinds are grown there for shade, windbreaks, street trees, honey, timber, fuel, and oil. A number of species can survive winter temperatures as low as 0°F, but even alpine species die if the ground freezes. A sheltered site, good drainage, and a heavy winter mulch may offer protection in marginal areas.

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