Brachychiton populneus

Brachychiton populneus, also known as the Kurrajong, is a Australian tree of medium size, particularly well adapted to the Mediterranean coast due to its limited hardiness and excellent drought resistance. With its slender appearance and pyramidal or rounded habit, it is decorative with its evergreen foliage in olive green. Its summer flowering in the form of clusters of bell-shaped flowers, white cream, pink to red inside, later gives way to elongated brown fruits. Tolerating most soils as long as they are well-drained, this tree grows in sunny locations. In case of severe frost, it easily regrows from the stump. 

Brachychiton is a genus of trees that includes 31 species, all native to Australia and Papua New Guinea. Formerly classified in the Sterculiaceae family, it now belongs to the large Malvaceae family, like Hibiscus, Linden or Baobab. Trees with a very ancient history, present on Earth for 50 million years, they are monoecious, meaning they bear separate male and female flowers.

B. populneus (formerly Sterculia diversifolia) is native to semi-arid areas of eastern Australia, where it has been used by Aboriginal people for multiple purposes: food (roasting seeds), utility (wood transformed into shields), agricultural (foliage used as fodder for livestock, etc.). It was then spread for ornamental purposes in different Mediterranean climate countries (South Africa, California, Spain, French Riviera, etc.).

This medium-sized tree reaches 10 to 12m (32ft 10in to 39ft 5in) in height, displaying a pyramidal habit with a dense crown that can become rounded with age. Similarly, its juvenile green bark gradually turns to grey, while the trunk thickens, sometimes even swelling after about fifteen years to store water, allowing it to withstand even semi-arid climates with rainfall of only about 300 mm (11.8in) per year. Its growth is relatively slow when left to itself, but much faster if it benefits from regular watering during the first years. It is adorned with evergreen or semi-evergreen foliage, depending on the winter it faces, in olive green. The leaves, about ten centimetres long, are alternate and generally simple, shaped like Poplar leaves, more or less obovate to elliptical and long acuminate. Sometimes, they can also be trilobed and take on a pinkish hue when they first appear, before turning green.
In summer, clusters of small bell-shaped flowers, 1 to 2cm (0.4 to 0.8in) long, composed of 5 to 6 elegantly recurved petals, like Lily of the Valley flowers, appear. They are white-cream to greenish on the outside, with a brighter interior, punctuated with purple-pink or red. Male flowers and female flowers coexist on the tree, the latter giving elongated fruits, 5cm (2in) long, brown in colour, resembling a slender ship's hull when dehiscing, revealing 3 to 8 orange seeds, 6 to 8mm (0.2 to 0.3in) in size.

This frost-sensitive tree withstands brief cold spells of around -7°C, which makes it one of the hardiest species of Brachychiton. This probably explains its wide distribution around the world. Another reason for its success is undoubtedly its very good drought resistance as well as its heat tolerance: temperatures of 40°C (104 °F) do not scare it! It grows in most soils, tolerating limestone well, but does not like stones and requires very good drainage.

This Brachychiton is a low-maintenance plant, accustomed to withstanding drought episodes. It is also capable of regrowing from the stump after exceptional frost. Used in urban plantings in favourable climates, it can be integrated into a diverse planting scheme with other exotic plants, especially shrubs, as it tends to branch relatively high. For example, plant a Viburnum lucidum at its base, an evergreen Viburnum with beautiful shiny dark green foliage, which curiously turns red-purple in autumn. Its fragrant white flowering precedes that of the Brachychiton in spring. Another drought-tolerant evergreen shrub, the Fremontodendron californicum, will dazzle you with its bright yellow flowering in June-July.