Eucalyptus robusta

Eucalyptus robusta, known as the White Mahogany Eucalyptus, is a tropical species originating from a coastal strip in southeastern Australia. It grows rapidly and thrives in humid soils and mild climates, forming a tree that reaches about thirty metres in height. Well adapted to coastal areas, it withstands salt spray and tolerates slightly salty soils. Its evergreen foliage is dark green, aromatic to the touch, and its cream-white flowering is not without interest. However, the brown and fissured bark is rather unattractive. Difficult to acclimate, this rare species will mainly interest collectors of the genus.

Eucalyptus robusta belongs to the large Myrtaceae family, which includes more than 130 genera, including Callistemon (bottlebrush), Feijoa, Guava (Psidium), and of course Myrtle. Among the 800 species in the Eucalyptus genus, only about ten are native to Southeast Asia, while all others come from Australia. E. robusta is derived from a coastal strip that extends from southern Queensland to southern New South Wales, in tropical and low-altitude regions. It is a tree that loves the sun and humidity, accustomed to rainfall of 1000 to 2000 mm (39.4 to 78.7 in) per year. It grows in wet to waterlogged soils, hence its common name Swamp Mahogany  which it owes to its reddish wood. It also tolerates slightly salty soils as well as wind and salt spray, conditions to which it is accustomed.
It is a fast-growing tree of medium to large size, generally reaching 25 to 30 m (82 to 98 ft 5 in) in height, but can reach up to 55 m (180 ft 5 in) (especially in Hawaii). The trunk is straight, measuring up to 1.20 m (3 ft 11 in) in diameter, and the brown bark is thick (2 to 4 cm (0.8 to 1.6 in)), fibrous, and fissured. In very humid climates, aerial roots can form from the trunk, up to 6 m (19 ft 8 in) above ground level. In open environments, it has a fairly wide habit, forming a crown with long, spreading branches, often brittle. When used in dense plantations, the branches are more upright and the tree narrower due to surrounding competition.
The evergreen foliage is alternate, with lanceolate petiolate leaves, 10 cm (3.9 in) long by 3 to 7 cm (1.2 to 2.8 in) wide for juvenile foliage, and 10 to 18 cm (3.9 to 7.1 in) long by 4 to 8 cm (1.6 to 3.1 in) wide for adult leaves. Dark green on the upper side, it is lighter on the underside and releases a spicy aromatic odour when crushed (due to the presence of numerous glands containing essential oils).
Flowering occurs from May to July in Australia, so in autumn and winter in the northern hemisphere. The flowers form pompom-like clusters about 3 cm (1.2 in) in diameter and cream-white in colour. Typical of Myrtaceae, it is mainly the stamens that are admired, with the flowers grouped in axillary umbels of 5 to 15. They are quite ornamental and nectar-rich. They then evolve into dark green cylindrical fruits that contain numerous seeds and often persist on the tree for two years.
Eucalyptus robusta grows in neutral to strongly acidic, clayey, and heavy soils, or even sandy-clayey soils. It appreciates very humid soils and can withstand temporary flooding. Although native to tropical areas, it can also grow in temperate climates and will tolerate brief frosts of around -2°C (28.4 °F) to -4°C when well established. Used as timber, it has been planted in many countries on different continents: Argentina, Brazil, Congo, Madagascar, China, Philippines, etc.

This Eucalyptus could be tried in the mildest areas of the Mediterranean coast, where it should withstand mild winters but may lack the humidity to develop well. The proximity of a water source or stream will then be welcome to help with its establishment. It will bring a touch of exoticism, combined with other characteristic plants such as the Dicksonia antarctica, a tree fern with magnificent foliage carried by a dark brown fibrous stipe. A beautiful palm tree with a tropical appearance like Archontophoenix cunninghamiana will also be a perfect companion, while a few plants of Hedychium, or Ornamental Ginger, with their long floral spikes will complete this scene.