BURSAGES

In addition to big sagebrush - a dominant species in the Great Basin Desert - several other aromatic shrubs with grey-green foliage are found across the North American deserts. These are bursages (Ambrosia species) with seeds that have spiky projections so that they are dispersed by attachment to animals' fur.

White bursage (Ambrosia dumosa)

Extensive stand of flowering white bursage (Ambrosia dumosa) in the Pinacate Biosphere Reserve (Sonoran Desert), Mexico.

White bursage is very common in the driest regions of the Sonoran and Mojave Deserts, where is can be the only major perennial plant apart from the similarly drought-tolerant creosote bush. It occurs frequently on fine silty or sandy soils. The leaves wither and are shed in periods of drought (often for most of the year).

White bursage growing on an arid slope in western California. Note the leafless, twiggy branches at the margins of these plants. For much of the year there would be no leaves at all.

Finely dissected leaves of white bursage

white bursage flowers (right) and developing burrs (left)

Triangleleaf bursage (Ambrosia deltoidea)

Triangle-leaf bursage is a dominant understorey shrub of the upper regions of the Sonoran Desert of Arizona, and an occasional shrub of other parts of the Sonoran Desert. It is not as drought-tolerant as white bursage. It characterisitically grows on slopes and rocky bajadas Click here for image, rather than flat silty areas.

Foliage of triangleleaf bursage

The bursages are not heavily grazed by animals, but they have one important role in desert environments: they frequently act as nurse plants for fishhook and pincushion cacti, protecting the delicate cactus seedlings during their early years of development.

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