Ambrosia dumosa – “White Burro-Sage”

Also Known As: Burro-Sage, Burro Weed, Burrobush, White Bur-Sage, White Bursage
Other Botanical Names: Franseria dumosa
Family: Sunflower (Asteraceae)
Bloom Period: Jan-Feb
Form: Perennial Shrub
Habitat: Widely found over large areas of the Mojave and Sonoran deserts below 5000 feet (1500 m), often codominant with creosote bush.
Leaves: Ovate, pinnately lobed; alternate
Translation: “Ambrosia” is Greek for “food of the gods,” which is funny since this plant is a preferred food of burros, as the common name makes clear; “dumosa” is Latin for “bushy” or “shrubby,” which is more straightforward. “Franseria” is named for Ant. Franser, an 18th Century physician and botanist of Madrid.
Notes: This plant is monoecious, meaning it has separate male and females flowers on the same plant. The males point down and drop pollen onto the females below, assisted by the wind. The female flowers are surrounded by bracts that look like burs, hence the name. It can (and does) naturally hybridize with its close relative, Cheesebush (Ambrosia salsola). Though it is not a large plant – growing no taller than 3ft (1m) – it can live over 75 years.
White Burro-Sage is widespread in the Mojave Desert, often intermixed with Creosote Bush at a spacing that is so even it appears artificial. This equal distribution is common among desert plants and usually reveals the maximum possible density of those plants in that area for the amount of water available. (Observe, for example, the sparse “forest” made by Joshua Trees). In the case of White Burro-Sage, however, studies have suggested that another factor is also at work: apparently its roots exude a compound into the soil that inhibits the growth of the roots of nearby plants, including Creosote Bush and other White Burro-Sage plants. This type of interaction is called “allelopathic” and is documented in other plants such as onions and common buckwheat, which also exude compounds from their roots that inhibit the growth of their neighbors.
Ronald Taylor offers additional information on why White Bursage and Creosote Bush grow together so often: “[T]hey use different adaptive strategies. Creosote bush has a deep root system and highly varnished evergreen leaves. Bur-Sage has an extensive shallow root system and white-woolly, drought-deciduous leaves. Creosote Bush endures the drought; Bur-Sage avoids the drought.” (“Drought-deciduous” means the plants sheds its leaves during dry periods to prevent water loss by transpiration.)
Animal Associations: Leaves eaten by the Desert Iguana and Chuckwalla. Larval food plant for the Desert Marigold Moth.