Sinojackia xylocarpa Seeds | Jack Tree

Jack tree with hanging white bell flowers and winged woody fruit on arching shoots — Jack Tree (*Sinojackia xylocarpa*): Styracaceae, low hills of Jiangsu and neighbouring eastern China.

LATIN NAME: Sinojackia xylocarpa

COMMON NAME: Jack Tree

Plant Profile

Jack tree is a small deciduous tree of the storax family, endemic to a few hills in Jiangsu and neighbouring provinces of eastern China. It grows three to seven metres tall, with a rounded crown, dark green leaves that turn yellow in autumn and, in April, hanging clusters of white, bell-shaped flowers along slender, arching shoots. The fruit is the distinctive part: a woody, egg-shaped drupe with corky wings, hanging from a long stalk and looking like a small wooden pendulum. It ripens in autumn and stays on the tree into winter. The species was described in 1928 from material near Nanjing, and it is now one of the rarest trees in China, with fewer than a few thousand individuals left in the wild.

Science & Biotechnology

Sinojackia xylocarpa is a monotypic genus named for the American botanist John George Jack, and its discovery was one of a series of finds that made the lower Yangtze a centre of botanical interest in the 1920s. It sits in Styracaceae, the family of snowbells and silverbells, and molecular work places it close to Halesia, which it resembles in flower but not in fruit. The winged, corky drupe is unusual in the family and is thought to be an adaptation for dispersal by water and wind along the low hills where it grows. The species is self-incompatible to a degree, and seed set in small populations is poor, which is one reason it has declined. It is listed as endangered in China, and most remaining sites are small groves on farmland edges, vulnerable to clearance.

Uses & Benefits

The tree is grown almost entirely as an ornamental and as a conservation subject, in botanic gardens and in a handful of Chinese parks. Its hanging white flowers and its strange, persistent fruit make it a fine specimen for a small garden, and it is one of the few trees that flowers well in partial shade. The wood is hard and fine but too scarce to use. In cultivation it is propagated by seed and by cuttings, and seedlings are distributed through botanic garden networks rather than the nursery trade. Its flowers are visited by bees and hoverflies, and its fruit is not eaten by wildlife, which may be part of why it spreads so poorly. Every plant in cultivation outside China descends from a small number of collections.

Growing from Seed

Germination is blocked twice over, by a hard shell and by an embryo that must after-ripen. Soak for a day, then stratify in damp sand at four degrees for three months. Sow in spring in a leafy, free-draining mix, one centimetre deep, and keep at fifteen to twenty degrees; germination takes four to eight weeks and is often partial. The seedlings are slow and should stay in pots for two years. Grow on in half shade, since the species scorches in full sun when young. Plant out in autumn into deep, moist, well-drained acid soil with leaf mould. Mulch and water through dry summers. Prune only to remove dead wood, as the natural shape is good.

Our Take

A rare Chinese endemic with hanging white bells and wooden fruit. Grow it as a conservation act as much as a garden tree.

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