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.

Distribution

Introduced; Australia, introduced also nearly worldwide.

Discussion

Species 700+ (15 in the flora).

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

None.

Lower Taxa

Eucalyptus camaldulensis, Eucalyptus citriodora, Eucalyptus cladocalyx, Eucalyptus conferruminata, Eucalyptus coolabah, Eucalyptus globulus, Eucalyptus grandis, Eucalyptus mannifera, Eucalyptus polyanthemos, Eucalyptus pulchella, Eucalyptus robusta, Eucalyptus sideroxylon, Eucalyptus tereticornis, Eucalyptus torelliana, Eucalyptus viminalis

Key

1	Inflorescences umbels in panicles.	> 2
1	Inflorescences umbels not in panicles or flowers solitary.	> 5
2	Leaves lemon-scented; trunk smooth; bark shedding in irregular pieces.	Eucalyptus citriodora
2	Leaves medicinal or spicy scented (not lemon-scented); trunk smooth or rough; bark fissured, fibrous, or shedding in flakes or irregular strips.	> 3
3	Capsules urn-shaped or truncate-globose, 8+ mm wide; juvenile leaves (common in mature crown) peltate, often reddish hirsute; Florida.	Eucalyptus torelliana
3	Capsules hemispheric, ovoid, or subpyriform, to 6 mm wide; leaves not peltate, not reddish hirsute; Arizona, California.	> 4
4	Leaf blades narrowly lanceolate, 8–17 × 0.8–2.5 cm.	Eucalyptus coolabah
4	Leaf blades round, elliptic, or ovate, 5–10 × 1.5–5 cm.	Eucalyptus polyanthemos
5	Flowers solitary in leaf axils, sessile or subsessile; capsules glaucous.	Eucalyptus globulus
5	Flowers 3–19 in umbels, pedicellate; capsules glaucous or not.	> 6
6	Trunk rough, brown, reddish brown, dark brown, or black; bark deeply furrowed, persisting on trunks and limbs.	> 7
6	Trunk smooth, gray, bluish gray, white, whitish gray, orange, tan, or mottled; bark shedding, occasionally rough near base (to ca. 1.5 m).	> 8
7	Bark soft, spongy, fibrous; trunk reddish brown; leaves light green abaxially; anthers present on all stamens; peduncles flattened; fruit valves fused after dehiscence.	Eucalyptus robusta
7	Bark hard; trunk dark brown or ± black; leaves same color on both surfaces; anthers absent on outer stamens; peduncles subterete; fruit valves free.	Eucalyptus sideroxylon
8	Capsules connate, forming globose clusters.	Eucalyptus conferruminata
8	Capsules not connate.	> 9
9	Leaves lighter in color abaxially.	> 10
9	Leaves same color on both surfaces.	> 11
10	Trunk mottled gray, orange, or tan; capsules ribbed; valves included; hypanthium length 3–4 times calyptra.	Eucalyptus cladocalyx
10	Trunk white; capsules smooth (not ribbed); valves exserted, incurved; hypanthium only slightly longer than calyptra.	Eucalyptus grandis
11	Inflorescences usually 3-flowered; juvenile leaves opposite, sessile.	Eucalyptus viminalis
11	Inflorescences 7- or 9+-flowered; juvenile leaves alternate, petiolate.	> 12
12	Leaf blades linear, 0.1–0.5 cm wide; fruit valves ± level with apex or included.	Eucalyptus pulchella
12	Leaf blades lanceolate, 1–3 cm wide; fruit valves exserted.	> 13
13	Leaves usually green to bluish green, sometimes grayish green; trunk powdery to touch.	Eucalyptus mannifera
13	Leaves green; trunk not powdery to touch.	> 14
14	Calyptrae of flowers mostly hemispheric, often rostrate, rarely bluntly conic; hypanthium length ± equaling calyptra.	Eucalyptus camaldulensis
14	Calyptrae of flowers conic-acuminate or horn-shaped; hypanthium length 2–3 times shorter than calyptra.	Eucalyptus tereticornis