Bursera
Bursera is a genus of aromatic, drought-deciduous trees and shrubs from the warmer parts of the Americas, ranging from the southwestern United States through Mexico and Central America into South America. Many species are pachycauls — plants with swollen, water-storing trunks — and several are prized in cultivation as caudiciform bonsai. Their resinous bark and foliage are the traditional source of copal incense, and the desert forms are widely known as elephant trees.
Description
Members of Bursera are small to medium trees and shrubs, typically with thick, tapering trunks and stout, often peeling bark. In many species the outer bark flakes away in papery sheets, sometimes revealing a colourful under-layer of green, red or bronze — a feature that, together with the fat trunks, makes them so appealing to succulent and bonsai growers. The wood and leaves are pleasantly aromatic when bruised, releasing the fragrant terpene-rich resin the genus is known for.
Leaves are usually pinnately compound (divided into small leaflets), though some species have simple or trifoliate leaves, and they are shed during the dry season, so plants often stand bare and sculptural for part of the year. The flowers are small and inconspicuous, usually greenish or cream, and are followed by small fruits that split to reveal a single seed in a coloured coat. Growth is strongly seasonal: plants leaf out and grow with the summer rains, then drop their leaves and rest through the dry months.
Distribution
Bursera is a strictly American genus. Its centre of diversity is Mexico, where dozens of species grow in seasonally dry tropical forest, thornscrub and desert. From there the genus extends north into the deserts of the southwestern United States, south through Central America, and into parts of South America and the Caribbean. The species most familiar to succulent growers, such as Bursera microphylla, are found in the hot, arid regions of northwestern Mexico and the adjacent United States.
Notable species
- Bursera microphylla — the elephant tree of the Sonoran Desert, a classic pachycaul with a fat pale trunk and fine ferny foliage; a favourite for caudiciform culture.
- Bursera fagaroides — the fragrant bursera, widely grown as bonsai for its peeling bark and quick-thickening trunk.
- Bursera simaruba — the gumbo-limbo, a larger tree with striking reddish, peeling bark, nicknamed the "tourist tree".
- Bursera hindsiana — a stout Baja California species with red-tinged bark, popular with collectors.
Cultivation
Most Bursera are easygoing given warmth, sun and sharp drainage. Grow them in a very free-draining, mostly mineral mix and give the brightest position you can — strong light keeps the trunk fat and the growth compact. They are true warm-season growers: water generously through spring and summer while in leaf, then taper off as the leaves drop and keep the plant nearly dry and warm through its winter rest. Cold, wet roots are the main danger, so keep plants above freezing and err on the dry side in the cool months.
Because their swollen trunks and flaking bark develop character with age, Bursera respond well to repotting into shallow containers and to the pruning and shaping used in bonsai. See Watering for seasonal technique.
In cultivation and hobby notes
For succulent and caudiciform collectors, Bursera sit at the crossroads of bonsai and pachycaul culture: the same plant can be grown as a chunky miniature "desert bonsai" or allowed to bulk up into a stout specimen trunk. Growers prize individuals with the fattest caudices and the most dramatic peeling bark, and the aromatic foliage is a bonus that few other bonsai subjects offer. Beyond the hobby, several species remain economically important as the source of copal, an incense resin with a long history of ceremonial and cultural use across Mesoamerica.
Propagation
Bursera can be raised from seed, though germination is often erratic and fresh seed gives the best results; seed-grown plants tend to develop the finest swollen trunks. Many species also grow readily from cuttings, which root quickly in warm conditions and are the usual way to bulk up bonsai stock and preserve a particular form — though cutting-grown plants may build a thick base more slowly than seedlings.
See also
- Bursera microphylla · Bursera fagaroides — representative species
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings