Eucalypt, gum tree [Greek eu, well, and kalyptos, covered, alluding to deciduous calyptra covering stamens in flower bud]

Matt Ritter
Leslie R. Landrum

Trees or shrubs, usually erect, glabrous or pubescent, hairs simple; bark shedding, smooth, or occasionally persistent near base of trunk, or rough throughout. Leaves heterophyllous, juvenile usually opposite, horizontal, sessile, blade base ± cordate, surfaces glaucous, adult usually alternate, vertical, petiolate, blade surfaces often same color, glandular; blade venation usually pinnate, faint, lateral veins ascending, nearly straight, several. Inflorescences 1–19-flowered, flowers solitary in leaf axils, or in umbels or panicles of umbels and axillary or terminal. Flowers 4- or 5-merous, sessile or pedicellate; hypanthium hemispheric, cylindrical, urn-shaped, pyriform, ovoid, obconic, or campanulate; perianth parts fused in a calyptra (called an operculum or bud cap) that is shed at anthesis; stamens often 100+, often showy, usually fertile; ovary 3–6-locular; ovules 10–100+, sterile ones often present. Fruits capsules, brown to gray, hemispheric, obconic, ovoid, subpyriform, globose, cylindric, or urn-shaped, glaucous or not, thick-walled, woody, usually smooth, opening apically; valves exserted beyond apex or included (enclosed) below fruit apex. Seeds several–100, cuboid, usually 1–3 mm, wind dispersed. x = 11.

Species 700+ (15 in the flora): introduced; Australia; introduced also nearly worldwide.

Species of Eucalyptus are some of the world’s largest flowering plants, some over 100 m; various species are most commonly planted as forestry and plantation trees for oil, timber, fuel, tannins, and paper pulp. Many are cultivated ornamentally in warm climates, with several naturalized in Arizona, California, and Florida, and, perhaps, other southern states.

Species of Eucalyptus in North America, where correlations with natural habitat do not exist, are often difficult to identify. Many species (over 200 in California alone) have been introduced into cultivation and more will surely be added.

Eucalyptus pulverulenta Sims has been reported to be naturalized in California but no supporting evidence has been found. Some putative hybrids have also been reported as naturalized.

In his treatment of eucalypts, M. I. H. Brooker (2000) included Angophora Cavanilles and Corymbia K. D. Hill & L. A. S. Johnson as subgenera of Eucalyptus, whereas other concurrent and more recent work has supported the status of Angophora and Corymbia as separate genera (P. Y. Ladiges et al. 1995; F. Udovicic and Ladiges 2000; D. A. Steane et al. 2002). Although the validity of the latter work is recognized herein, for the purpose of simplicity in treating a small group of naturalized species, Eucalyptus in the broad sense of Brooker is here adopted.

SELECTED REFERENCES Brooker, M. I. H. 2000. A new classification of the genus Eucalyptus L’Her. (Myrtaceae). Austral. Syst. Bot. 13: 79–148. Chippendale, G. M. 1988. Myrtaceae—Eucalyptus, Angophora. In: R. Robertson et al., eds. 1981+. Flora of Australia. 32+ vols. Canberra. Vol. 19.