The Styrax Tree: Botany of Styrax benzoin and Styrax tonkinensis

The benzoin trees are members of Styrax, a genus of about 130 species of shrubs and trees found across warm parts of Asia, the Americas and one corner of the Mediterranean. Most produce a little resin when wounded. Only a handful produce enough, of the right kind, to be worth tapping.

The genus

Styrax belongs to its own family, Styracaceae, in the order Ericales, which also holds tea, persimmon and heather. The trees are mostly small to medium, deciduous or evergreen, with simple alternate leaves, often with a felt of star-shaped hairs underneath. The flowers are the family signature: white, five-lobed, bell-shaped, hanging in small clusters and often fragrant. The fruit is a round drupe with one or two seeds.

Gardeners know the ornamental species, Japanese snowbell (S. japonicus) and fragrant snowbell (S. obassia), grown for their spring flowers in temperate climates. The Mediterranean has one native, S. officinalis, which was the original source of a resin the Greeks called styrax, before the word migrated to a different tree entirely.

The benzoin species

Styrax tonkinensis (Siam benzoin) is a fast-growing deciduous tree of the mountains of northern Laos and Vietnam, reaching twenty metres or more. It is a pioneer: it colonizes fallow upland fields readily, which is why Lao farmers grow it in rotation with rice rather than in orchards. It is tapped from about seven years of age. Its resin is the pale, benzoate-rich Siam benzoin. The species is also grown for pulpwood in parts of Asia.

Styrax benzoin (Sumatra benzoin) is an evergreen tree of the humid highlands of Sumatra and the Malay Peninsula, up to thirty metres in the wild, kept smaller in cultivation. It is planted in kemenyan gardens and tapped for decades. Its resin is darker and cinnamate-rich.

Styrax paralleloneurus is a close relative grown alongside S. benzoin in the same gardens; its resin is traded under the same name and is sometimes considered the better grade locally.

Growing conditions

The benzoin species want tropical highland conditions: elevations of a few hundred to over a thousand metres, high humidity, rainfall spread through the year with a marked drier season for tapping, and well-drained soils on slopes. They tolerate poor soil and are used in Laos partly for that reason. They do not tolerate frost.

Cultivation and the resin

The tree makes resin in response to wounding, in specialized cells that form where the bark is cut. Undamaged trees produce almost nothing. Farmers therefore tap: shallow cuts in the dry season, collection two to three months later. The full process is described in How benzoin is harvested.

Trees are tapped for ten to fifteen years in Laos and considerably longer in Sumatra. Yields peak in early maturity and decline. Because both systems are smallholder agroforestry rather than plantation monoculture, they keep tree cover on hillsides and need no inputs beyond labour. The economic weakness is price: when benzoin pays poorly, the gardens are not renewed.

Styrax versus storax

The confusion is old enough to have its own history. The Greek styrax was a resin from Styrax officinalis. When benzoin arrived from the east it was compared with it, and when Liquidambar balsam from Asia Minor entered the trade it was sold as “liquid styrax” or “storax”. Linnaeus then named the benzoin tree Styrax benzoin. The result: today Styrax (the genus) is the benzoin tree, and styrax or storax (the material) is Liquidambar balsam, which comes from an unrelated family. See Benzoin vs styrax and Storax.

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• botany
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