Herb To Know: Eucalyptus

This herb isn't just for cough drops. Learn what else eucalyptus has to offer you.

| April/May 2002

Eucalyptus spp.
Family Myrtaceae Tree

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 tress and shrubs, and the familiar medicinal smell is just one in the spectrum of fragrances found in this aromatic genus.

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.

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.

Plants range in height from a few feet to 380 feet (E. regnans—known as mountain ash—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.

Blue gum (E. globulus) is the most commonly planted eucalypt in the world. Its outer bark is constantly shedding, and this tendency along with its falling fruit caps makes it undesirable as a street or landscape tree. The smooth inner bark is gray or white. It has large white, mostly solitary flowers. Its mature height of 70 to 140 feet is much too tall for smaller gardens, but a cultivar, E. g. ‘Compacta’, is shorter and quite hardy.

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