Picrasma quassioides - Quassia

Picrasma quassioides, or Japanese quassia, is a little-known Asian tree with moderate growth, ornamental for its pinnate leaves and autumn colours. It is a very hardy species that adapts to ordinary, but deep and cool soils, in non-scorching sun or partial shade. It integrates well into urban or natural gardens, as a standalone specimen or at the edge of woodland.

Belonging to the Simaroubaceae family, Picrasma quassioides is a spontaneous botanical species in the temperate mountains of Asia, from the Himalayas (Kashmir, Nepal, Bhutan, India) eastwards to northeastern China (many provinces up to Yunnan and Shaanxi), Taiwan, Korea, and Japan. It grows mainly in mixed montane forests, most often below 3,200 metres in altitude.
A deciduous tree, usually multi-trunked, the Japanese quassia reaches 4 to 8 metres in height with a spread of 2.50 to 4 metres, sometimes up to 10-12 metres for older specimens; expect 4 metres in height at 10 years of age under good conditions. The young shoots, brown-red to purple with distinct pale lenticels and large foliar scars, become grey and finely fissured with age; the reddish buds are densely pubescent. The alternate leaves measure 15 to 40 cm in length. They are compound with 9 to 15 leaflets 2.5 to 10 cm long, ovate to lanceolate, with a distinctly dentate margin; their main vein often reddens in season. The autumn colour of the foliage varies from yellow to scarlet depending on the soil and sunlight. Flowering occurs from April to May, or even into June in cool climates. It appears in loose cymes 15 to 20 cm long that arise in the leaf axils; the small greenish flowers, about 8 mm, bear 4 or 5 sepals and petals. This species is primarily dioecious: male and female plants are separate, although bisexual flowers are sometimes observed on the same inflorescence. The fruits on female plants are ovoid drupes 6 to 8 mm long, turning from red to blue-black at ripeness. The root system is rather spreading and fibrous; the plant does not sucker, but it can regrow from the stump after a severe cold spell.
This small tree is hardy down to -20 °C, or even a bit less in a sheltered position. In the garden, it appreciates fertile, deep, cool but well-draining soil, acidic, neutral, or calcareous, and thrives in gentle sun or partial shade; it shows some tolerance to drought once established.

Use Picrasma quassioides as a small subject for bright partial shade, plant it sheltered from dry winds, where its foliage will bring autumn colour. In cool soil, it makes a nice effect at the edge of a border, accompanied by other small trees. Pair it, for example, with Acer palmatum 'Sango-kaku', Cornus kousa 'China Girl', Styrax japonicus 'Snowfall' and Amelanchier 'Ballerina'.

The specific name quassioides means "resembling Quassia": in the 19th century, its very bitter bark was compared to that of Quassia amara, an American tree named in honour of Quassi, a healer from Suriname who popularised its uses. This bitterness comes from quassinoids studied for their antibacterial, insecticidal properties and as bittering agents, sometimes even cited as a hop substitute. In several regions of Asia, the bark and wood have been used as a bitter tonic or traditional insect repellent.