Koelreuteria bipinnata – Two-pinnate Bladder Senna (Chinese Flame Tree)
Koelreuteria bipinnata, the two-pinnate bladder senna, known as the Chinese flame tree, is one of the few trees that bloom in the height of summer. It belongs to the soapberry family (Sapindaceae) and captivates with large clusters of yellow flowers and spectacular pink-salmon, lantern-like seed pods.
Synonyms and Nomenclature
The species was described by Franchet (1886). The Kew POWO database lists several synonyms for it, including:
- Koelreuteria integrifoliola Merr.
- Koelreuteria bipinnata var. integrifoliola (Merr.) T.C.Chen
- Koelreuteria bipinnata var. puberula Chun
In English, the plant is known as "Chinese flame tree," "Chinese golden rain tree," and "bougainvillea goldenraintree"; in Chinese, it is called 复羽叶栾树, and in German, it is sometimes called Blasenbaum; the Polish name is two-pinnate bladder senna.
Origin and Appearance
The species originates from south-central and southeastern China to northern Vietnam; it was discovered in Yunnan in 1886. It is a deciduous tree growing 7–20 m tall, with few branches and a rounded to flattened crown, typically living 50–150 years.
The leaves are large, bipinnate (hence the name "two-pinnate"), green, turning yellow in autumn. In summer, the tree produces impressive, branched, terminal panicles 20–50 cm long, composed of small yellow flowers with a red-orange center. The most distinctive feature, however, is the fruit – three-lobed, inflated, papery pods 3–6 cm long, resembling small Chinese lanterns, initially pink to salmon-colored. Inside are hard, black, spherical seeds.
Frost Resistance and Cultivation
The Bladder Senna is frost-resistant (USDA zones 7–9) and adapts well to the Central European climate. It requires full sun for abundant flowering and a nice shape. It is exceptionally undemanding: tolerates poor, clayey, sandy, and alkaline soils, is very resistant to drought, wind, salinity, and urban pollution, and rarely gets sick.
Cultivation from seeds
The seeds have a hard, impermeable coat and double dormancy. Before sowing, the physical dormancy must be broken—by scarification (cutting or rubbing the coat) or a hot water bath (pouring boiling water over and soaking until swollen, about a day). Cool, moist stratification (about 30–60 days at 4°C) or sowing in a cold frame over winter also helps. After breaking dormancy, fresh seeds germinate quickly and readily, so the plant also self-seeds easily.
Care and uses
This popular ornamental tree is used in streets, parks, and avenues, valued as a summer flowering accent and for its long-lasting, lantern-like seed pods. Seeds have been used as beads, and the flowers provide a yellow dye. It is worth remembering that in warmer regions the plant self-seeds readily and can be somewhat invasive—though usually less so than the related Koelreuteria paniculata.
Interesting facts
The striking pink “petals” are actually not flowers but inflated, papery seed pods shaped like miniature Chinese lanterns—often more decorative and durable than the yellow flowers themselves. The species was discovered by the French missionary and botanist Père Delavay, who collected it in Yunnan the same year Franchet formally described it.
Summary
The Bladder Senna is a charming “twice ornamental” tree—first with yellow panicles in midsummer, then with pink lantern-like pods. Growing from seed is easy if the hard coat is broken, and in return, you get a hardy, low-maintenance, and highly decorative tree.
