Most of the 30 odd species of the genus Brachychiton are endemic to Australia. Most species are more commonly known as kurrajongs of one sort or another. They are found chiefly in northern tropical and subtropical areas with a few appearing in arid zones. They produce stunning sprays or clusters of colourful blooms, often on bare branches before the new foliage appears. The trunks are shapely and sometimes swollen. Large, boat-shaped woody seed capsules appear after flowering is finished. These trees are very popular as ornamental specimens and are often seen in parks or gracing suburban streets. Most of the species are favoured by birds.
Brachychiton acerifolius is native to Queensland and New South Wales. It is also known as Sterculia acerifolia. It is a popular and well-known species, better known by its common names of Australian flame tree, Illawarra flame tree or flame kurrajong.
It may grow to 40 metres in its rainforest locale but is usually a smaller tree in cooler areas. It is a deciduous tree and has a very profuse display of dull pink to red, bell-shaped flowers from November through to March. The flowers are followed by brown, woody fruits of 7 to 12cm long. It has some tolerance to frost. It is best to buy grafted specimens for the home garden as seedlings may take many years to flower.
Brachychiton populneus (synonym Sterculia diversifolia) or Kurrajong is a very popular, and quite spectacular, ornamental tree widely grown for shade and shelter or as a street tree. Young plants are often grown indoors. It has cream or pink, bell shaped flowers with red markings inside. The flowering season is mainly from October to February. It is semi-deciduous with greenish bark. This is quite a large tree reaching to 20 metres. It has good frost tolerance.
Brachychiton rupestris (synonym Sterculia repestris) or Queensland bottle tree has a distinctive swollen trunk which may be up to 2 metres in diameter. It is a semi-deciduous tree from dry inland Queensland. In spring and early summer, clusters of yellowish bell-shaped flowers are borne but remain hidden in the foliage.
One of the smaller species is Brachychiton bidwillii, also known as the dwarf kurrajong or little kurrajong. It grows to five metres and come from the east coast of Queensland. It is deciduous in dry periods and has deeply lobed leaves which are shed in late spring when the flowers appear. The flowers are borne in compact clusters and are tubular and deep pink or red in colour. This variety is seldom seen in cultivation.
Another with the common name of kurrajong is the white kurrajong or lacebark kurrajong. It may also be called the scrub bottle tree. Its scientific name is Brachychiton discolor. It is endemic to Queensland and New South Wales and grows to 30 metres. It is native to marginal rainforest and does not reach its potential height in cooler areas. It produces very prolific displays of dull pink to red, bell-shaped flowers from November to March. The flowers are followed by brown woody fruits of 7 to 12cm long.
Brachychiton have some tolerance to frost once established. They are generally slow-growing while young and produce their best floral displays if grown in a warm climate. They prefer a well-drained, acidic soil in a position that receives full sun.