Floral rain and flames brighten Chinese urban forest

I'll finish the year with another story from Chongqing, in central China. While visiting in October I noticed smudges of orange and red in the plentiful urban forests around the city. Firstly from my hotel room, then from the pagoda viewing platform at Eling Park, and to be fair, pretty much from every vantage point in the city...

They are part of the remnant or regenerated forest that carpets the hillsides in Chongqing, but also planted in formal garden beds and as a street tree.

You might call them golden rain, flames or bougainvillea-like-sprays. These words combine to provide some of the names for the local Koelreuteria bipinnata with its orange-shaded, puffy, three-winged, papery fruit.

The Bougainvillea Golden Rain Tree as one common name has it, has small, yellow flowers, with a fleck or red at the base of the petals. But the flowers are produced in large clusters, presumably the golden rain. Or maybe that's the flush of yellow leaves in autumn? The Chinese Flame Tree common name hints strongly to its origins, and to the colour of the fruits. 

There are three species, two in China and Japan and one split between Taiwan and (apparently) Fiji. All seem to be tolerant of tough urban conditions, tolerating pollution and 'challenging' soils.

Koelreuteria paniculata typically has once divided leaves (or barely twice 'pinnate') and grows naturally in China, Korea and Japan. In China it occurs in Anhui, Gansu, Hebei, Henan, Liaoning, Shaanxi, Shandong, Sichuan and Yunnan, but is widely planted elsewhere, including Australia. 

Koelreuteria elegans subspecies formosana only grows naturally in Taiwan and has 'leaflets' (the ultimate leafy bits in the divided leaf) with a strongly oblique base. It is planted and weedy in northern Australia.

I'm thinking the species I saw and photographed in Chongqing is the third species, Koelreuteria bipinnata, with twice pinnate leaves (see above). It comes from natural forested slopes in Guangdong, Guangxi, Guizhou, Hubei, Hunan, Sichuan and Yunnan, as well as Japan. Until the 1990s, Chongqing was part of Sichuan so I'm presuming the species is more or less native to the area.

According to John Grimshaw and Ross Bayton's New Trees: Recent Introductions to Cultivation, Koelreuteria bipinnata was introduced into France in 1887 and California in 1911. It didn't become popular in Europe but is now widespread in warmer parts of North America. Although not considered 'hardy' in Lonon and Paris, Grimshaw and Bayton suggest that with the changing climate it is worth planting now in southern England. In Australia this species is rarely planted but there are three specimens in Melbourne Gardens, two near the Plant Craft Cottage.

In terms of which species to try, there is not much in it. All three are relatively minor variations on a theme, even with the additional flourishes such as pink new growth and pinker fruits available in cultivars of paniculata. And they should all do well in the warming, drying climate predicted for southern Australia. Possibly too well of course and I'd prefer to not see golden rain and fruity flames from every vantage point in Melbourne.