Description
Chinese Rain Tree (Koelreuteria elegans subsp. formosana) is a small to medium deciduous tree. In Australia it grows to approximately 5 m tall and up to 18 m under ideal conditions. It has a light brown, smooth trunk which can develop ridges with age. Its dense, rounded crown which can reach 10 to 15 m in diameter. Its leaves are bipinnate (i.e. the leaflets are borne on a secondary axis from the main leaf axis). Each leaflet is hairless, dark green above and light green below and usually has coarsely toothed edges with a long tapering point. Along with its attractive shape and size Chinese Rain Tree has showy branched clusters of small, yellow flowers with five petals in spring and summer. Fruits are inflated, papery capsules up to 50 mm long in drooping clusters. They range in colour from light pink to a deep rose and contain black round seeds approximately 5 mm in diameter.
Due to its attractive appearance and general hardiness it has been used as an ornamental tree in many parts of the world. It is also recorded as a weed in Japan and parts of the United States (e.g. Florida, Louisiana, Texas, Mississippi and Hawaii).
For further information and assistance with identification of Chinese Rain Tree contact the herbarium in your state.
Distribution:
Naturalised and well established in Brisbane and near Noosa in Queensland and near Lismore in New South Wales, where it is invading urban parks, bushland, gullies and streets. It has been declared an environmental weed by the Brisbane City Council and the Ipswich Council. It is also likely to be naturalised in other areas of the north coast of New South Wales. There is also the potential for distribution in Western Australia and the Northern Territory.
Habit:
Tree
Key points:
Chinese Rain Tree (Koelreuteria elegans subsp. formosana) is an attractive deciduous tree that has been planted for ornamental purposes in the past, especially as a street tree It tolerates a variety of environmental conditions and has a high growth rate and high seed viability. It has naturalised and become invasive in Australia, particularly in south-east Queensland and the north coast of New South Wales, and has the potential to crowd out native vegetation. Currently, there are relatively few infestations. If new infestations are reported early enough to the appropriate authorities further spread can be controlled and eradication may be possible.
How it spreads:
Chinese Rain Tree reproduces by seed, which can germinate within 6-8 days. While the papery fruits suggest that it could be dispersed by wind the relatively large size of the seeds (at least 5mm) suggests otherwise. The infestation of gullies in Brisbane suggests that movement by water may play a role. Birds may also disperse the seeds attracted by the colourful, plentiful fruits and seeds.
Where it grows:
Chinese Rain Tree is tolerant of a wide range of environmental conditions. It thrives in temperate and subtropical climates. It tolerates full sun, partial shade, drought, frost, heat, well drained to wet soils, extended flooding and air pollution. It grows on a wide range of soil types and may be tolerant of light salt spray, but not of saline conditions.
Flower colour:
Yellow
Distribution map:
Impacts:
Chinese Rain Tree is on the Alert List for Environmental Weeds, a list of 28 non-native plants that threaten biodiversity and cause other environmental damage. Although only in the early stages of establishment, these weeds have the potential to seriously degrade Australia’s ecosystems.
The rapid growth rate and high seed viability could lead to it crowding out native plants.
Origin:
Chinese Rain Tree is a native of Taiwan where it is apparently fairly widespread.
History:
No records could be found of when this species first arrived in Australia. Its use as a street tree in many regions suggests that it was imported for ornamental purposes. In Brisbane Chinese Rain Tree was commonly planted as an amenity/ street tree until the early 1980s when it was recognized as an environmental weed.
