Biancaea sappan Seeds | (syn. Caesalpinia )

Prickly branches and small yellow flowers of sappanwood with reddish heartwood exposed on a cut stem — Sappanwood (*Biancaea sappan*, syn. *Caesalpinia sappan*): Fabaceae, dry forest of South and Southeast Asia.

LATIN NAME: Biancaea sappan (syn. Caesalpinia sappan)

COMMON NAME: Sappanwood

Plant Profile

Sappanwood is a small, spiny tree or large shrub of the pea family, four to ten metres tall, with prickly branches, bipinnate leaves and small, yellow, five-petalled flowers in loose terminal clusters. The trunk is grey and relatively smooth, and the wood inside is the point of the plant: a deep orange-red heartwood that has been cut, chipped and boiled for dye for at least two thousand years.

The species is native to the dry forests and monsoon woodland of India, Myanmar, Thailand, Laos, Vietnam, southern China and parts of Malesia, and it has been carried so widely by trade that its original range is uncertain. It grows on poor, dry, stony ground, tolerates drought and light frost, and flowers in the dry season before the new leaves are fully out.

The pods are flat, leathery and brown, and the seed inside is hard and oval. The tree is thorny enough to make an effective hedge and has been used as one across its range, which is one reason it turns up in odd places along old trade routes.

For a gardener, the appeal is the combination of fine, feathery foliage, a dry-season display of yellow and the unusual red heartwood that shows when a branch is cut. It is a plant of warm, dry climates, and it will not tolerate wet feet or hard frost.

Science & Biotechnology

The red pigment is brazilin, a homoisoflavonoid that oxidises to brasilein and gives the characteristic deep red to purple colour of the dye. The chemistry is closely related to that of brazilwood, the American tree formerly placed in the same genus, and the two dyes were traded as the same commodity for a century. That confusion is worth untangling, because it is the source of a widespread error.

The name Brazil does not come from sappanwood. It comes from pau-brasil, the brazilwood of the American tropics, now Paubrasilia echinata, which grew in such abundance on the coast of the country that the land was named for the trade in its red dye. Sappanwood was the Old World equivalent, and the two were sold side by side in European markets, but the naming of the country belongs to the American tree. What the two share is a pigment chemistry based on brazilin, not a name.

The pharmacology of sappanwood is a small field of its own. Extracts of the heartwood have shown anti-inflammatory, antioxidant and immunomodulatory activity in vitro and in animal models, and brazilin has been studied for its effects on glucose metabolism and on inflammation. Brazilian researchers have also examined the related brazilwood for similar activity. None of this has produced a standardised medicine, and the human evidence is thin.

The seed is hard-coated and water-impermeable, a common adaptation in the genus for surviving long dry seasons. In the wild, germination follows fire or heavy rain that softens the coat, and the seedling establishes quickly in the disturbed ground that follows. The tree is also known to nodulate with rhizobia, though the symbiosis is less studied than in crop legumes.

Uses & Benefits

The heartwood is the traditional product. Chipped and boiled, it gives a red dye used for silk, cotton and wool across Asia, and the colour is mordanted with alum for a clear red or with iron for a darker, purplish tone. It is still used in traditional textile crafts in Thailand, India and Indonesia, and it appears in the dye lists of craft dyers in Europe and North America as a reliable red.

In Chinese medicine, Su Mu, the heartwood, is used to promote blood circulation, to relieve pain and to reduce swelling, and it appears in formulas for traumatic injury and for menstrual disorders. The evidence is traditional rather than clinical, and the plant should not be used as a self-treatment for a serious condition such as a thrombosis.

The tree is also grown as a hedge and a boundary plant in dry country, and its wood is used for small turnery and for fuel. It is a honey plant, and the flowers are visited by bees. In parts of Southeast Asia the young leaves are eaten cooked as a vegetable, though the prickles make the harvest a chore.

For a garden, the plant is a warm-climate curiosity. It is worth growing for the yellow flowers, the feathery foliage and the novelty of a tree that bleeds red when cut, and it is a useful small tree for a dry, stony site. It is not a plant for a cold garden, and it should be sited well away from paths because of the prickles.

Growing from Seed

Seed needs scarification. Nick the hard coat or rub it on sandpaper, then soak in warm water overnight until the seed swells. Sow into a loose, gritty, free-draining mix, cover lightly and keep at twenty-two to thirty degrees in bright light. Germination is usually two to five weeks, and untreated seed can sit for months.

Grow the seedlings in full sun and keep the water moderate; this is a dry-country tree and overwatering causes root rot. Pot on as the root fills the container, and plant out into a stony, well-drained site once the plant is sturdy and the risk of frost has passed. Prune lightly to shape the tree while it is young, since the prickles make later pruning unpleasant. In cool climates it can be grown in a large pot and kept dry and frost-free in winter.

Our Take

Sappanwood is a plant with a good story and a real use: a small, thorny, dry-country tree that gives a red dye, a hedge and a dry-season display of yellow. It is also the perennial victim of a historical mix-up, and it is worth growing partly so that the difference between it and the American brazilwood can be explained properly.

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