Common Names
Elephant Tree, torote, torote colorado, copal

Habitat
The genus Bursera is affiliated with the tropics and subtropics; B. microphylla is one of several species that have radiated into more arid environments. This distribution is nearly coincident with the extent of the Sonoran Desert. B. microphylla grows on virtually all the gulf islands, which are presumably too arid to support other species of Burseraceae. The peninsular and mainland populations have distinct terpene compositions, which suggest a long period of separation.

Bursera microphylla is rare to locally common in washes, on gravelly plains, and on rocky limestone or igneous slopes. It typically grows in the warmest microhabitats at the northern end of its range, often south-facing slopes of low desert mountain ranges. The northernmost outpost in Arizona (33.7 degrees N, 113.4 W), a sighting by Paul R, Krausman, and Jon J. Hervet, is in the Harquahala Mountains on steep canyon slopes and in the canyon bottom. It is also thought to exist in the Harcuvar Mountains, but the sightings have not been confirmed. In central Sonora and Baja California Sur, where frost is infrequent, B. microphylla is more evenly distributed.

The cold limits the northward and upward penetration of the species. Temperatures below -3 C will kill the plant to the ground, but they often recover if the roots escape the freeze. The periodic cold winters of Arizona tend to keep B. microphylla heights below 2 meters, but larger specimens exist in special microhabitats, like the Sierra Estrella Mountains south of Phoenix.

Flowers
flowers yellow with 5-10 petals,6 mm diameter, often blooming before other foliage.

Description
Considered a small shrub or tree, Bursera microphylla, has aromatic leaves on cherry-red branches. The bark of the main trunk is whitish and exfoliates in thin sheets. The trunk and lower branches are thickened out of proportion to the height of the plant. The odd-pinnate leaves, 3-8 cm long, have 7-35 small, linear, glabrous leaflets and are alternate or clustered in short shoots. The leaflets are 6-12 cm long and 1-2.5 mm wide. The conspicuous flowers are single or in few-flowered clusters. Fruits are 3-angled, dark blue, or purple drupes containing a single seed.

Bursera microphylla stores water in the conductive and parenchymal tissues of the trunk, lower limbs, and wood. The sarcocaulescent habit acts as a buffer against variation in environmental water balance. It is especially common in the Central Gulf Coast subdivision and parts of the Vizcaino region, where a year or more might pass without measurable rainfall.

The bark contains tannins and was gathered in Sonora for export. Parts of the plant can be used medicinally, and new drugs are being developed from its unusual chemistry. The Seri Indians use B. microphylla for fuel, shampoo, medicine, and paint. The fruits are an important food for gray vireos and other birds throughout winter and early spring.

References:
Benson, L. (1943). Revisions of Status of Southwestern Trees and Shrubs. American Journal of Botany 30: 230-240.

Turner R., Bowers J., and T. B. (1972) Sonoran Desert Plants. Tucson: University of Arizona Press.

Comments
Burseria microphylla is a unique plant found in our state. Specimens can be seen at the Estrella Mountains, from the Butterfly Trail, or off-trail on the southern slopes.