Eucalyptus

The genus Eucalyptus comprises about 700 species of very aromatic trees and shrubs. All the species that exist on the Canary Islands are introduced (allochthonous). Sometimes they have two types of leaves, all persistent, simple, hairless and with an entire margin. The leaves of young specimens are opposite, wide and often lack stalks, while those of adults are more elongated, alternate and always have an obvious stalk. The French novelist Jules Verne wrote about the canopy of Eucalyptus leaves in In search of the Castaways: "The trees lose their bark every year, instead of their leaves; […] the leaves present their sides to the sun and not their face, and consequently give no shade..." The flower buds have a hard, variably-shaped cap (operculum). When these open they drop off to expose numerous white, yellowish or pinkish stamens. The flowers are very melliferous, and are often borne in groups in the axil of the twigs. The fruit is a capsule (like a small pot with a lid), greenish, brownish or greyish in colour depending on how ripe it is, which contains abundant small seeds.

Many species are cultivated on the Canary Islands, of which four have become established in the wild:

1. Eucalyptus camaldulensis Dehnh. Eucalyptus, River Red gum. Tree up to 50 m tall. Shedding, smooth whitish-grey to brown-red bark. Young leaves are 6-12 cm long and 2-4 cm wide, whitish-blue, lanceolate, and acuminate; adult leaves are 8-25 (30) cm long, 0.7-2.5 (4) cm wide, narrowly lanceolate, somewhat curved with a long tip, and light green in colour. It is included in the Atlas of invasive alien plants of Spain.

2. Eucalyptus cornuta Labill. Yate, mo, yandil, yeit. Tree up to 23 m tall. Non-shedding, dark or almost black bark that is deeply cracked at the base and smooth in the upper part. Young leaves are opposite, widely lanceolate to orbicular, dark green in colour, with a leaf stalk; adult leaves are alternate, narrowly lanceolate, up to 12 cm long and shiny dark green on both sides.

3. Eucalyptus globulus Labill. Eucalyptus, Tasmanian blue gum, southern blue gum, blue gum. Can be as much as 40 m tall (some Tasmanian specimens are 100 m). Smooth bark that is shed in wide strips with a bluish-grey waxy covering (bloom) that gives it the name 'blue gum'. The young leaves are 4-16 cm long, 1.5-9 cm wide, oval or oval-lanceolate, with no stalk; adult leaves are 8-35 (40) cm long, 1.5-4 cm wide, lanceolate and sickle-shaped, curved with an elongated tip. Flora iberica differentiates the subspecies globulus and maidenii (F. Muell.) J.B. Kirkp. This species is included in the Atlas of invasive alien plants of Spain.

4. Eucalyptus rudisEndl. Normally a medium-sized tree from 5-20 m tall. Non-shedding bark, generally rough and dark or light grey in colour. Young leaves are opposite; adult leaves are alternate, 9-18 cm long and 1.5-4 cm wide, ovate to orbicular, somewhat curved, terminating in a point, opaque greyish green in colour and with a leaf stalk.