Ambrosia dumosa (with fruit)
Location in Utah
Ambrosia dumosa (flowers)
Close-up of A. dumosa
Family: Asteraceae
Group/Duration: Dicot/perennial
Location: Ambrosia dumosa is native to the US. It can be found in the deserts of Arizona, California, Nevada and Utah.
Size: At maturity the plant reaches 2 ft. tall with the roots extending to a minimum of 12 inches deep. The leaves are 0.5-4 cm. long. As it grows the roots will grow five to 15 times faster than the stem. The root to shoot ratio is 1.38.
Flowers: Ambrosia dumosa has yellow flowers that are 3-5 mm. in diameter. The plant can bloom in nearly any season, depending on the amount of rain. The most common time to see blooms are in late winter or early spring.
Growth: Ambrosia dumosa grows fairly rapidly, in part due to its short life span. It grows at elevations up to 3000 ft. A. dumosa can survive to a minimum temperature of negative 11 degrees Fahrenheit. A minimum of 250 frost free days are required for growth. A. dumosa leafs out in February or March and goes dormant during periods of drought. The plant has a low moisture use and is highly drought tolerant. Soft gray-white hairs cover young stems, leaves, and sometimes flowers. These hairs decrease the amount of water loss. A. dumosa is intolerant to shade and has moderate salinity tolerance. The optimal soil pH for growth is 7 to 8.5. Growth is inhibited by Creosote bush (Larrea tridentata). Human impacts such as pollution from electric generating plants, sulfur dioxide, and nitrogen dioxide fumigation all inhibit growth and can cause plant death. It takes 40 years for the plant to decay upon death.
Reproduction: Ambrosia dumosa has both vegetative and sexual reproduction. Its pollen is distributed by wind. A. dumosa produces a bur-like fruit which ranges in color from brown to golden to purple. The fruit has between 12-35 flat spines which can be up to 9 mm. long. Seeds are black in color and also have prickled spines. The spines allow the seeds to be distributed by the wind and by mammals. These seeds germinate best at 35 degrees Fahrenheit. The seeds are highly abundant and have a moderate dispersal spread with high seed vigor. High seed vigor gives the seeds a better chance of survival to germination.
Plant Associations: Ambrosia dumosa is found in open spaces within communities of Creosote bush. The plant is also associated with many species of plants found in the Mojave Desert. Such species include the Joshua tree, saguaro, Sonoran creosote bush scrub, Mojave creosote bush scrub, and Mojave mixed woody scrub. As stated previously Creosote bush limits the growth of A. dumosa, possibly by inhibiting root growth. One trait of Ambrosia dumosa is that it acts as a nurse plant once it is established. As a nurse plant A. dumosa provides protection and improves the microclimate for growing seedlings. A. dumosa seems to fair better over time if it does not establish under a nurse plant, due to competition for resources. One other association of A. dumosa is with Sandfood, a parasitic plant. Sandfood is considered a very valuable food resource for desert peoples.
Economic and Ecological Impacts: Ambrosia dumosa provides food for humans due to its parasitic relation to Sandfood. By itself A. dumosa is not a very palatable food source for humans. Livestock and other grazing animals also seem to find A. dumosa unpalatable. Horses will eat A. dumosa as will feral asses. Usually most consumption of A. dumosa occurs when there is a lack of other food resources in the area. The seeds are often eaten by desert rodents. Ambrosia dumosa pollen is considered highly allergenic with many people being affected by it.
Ambrosia dumosa has another economical and ecological impact, because it is considered to be fire resistant. The fire resistance is due to the fact that A. dumosa grows in sparse communities making it difficult for the fire to travel from one plant to another. Ambrosia dumosa is also currently being studied as a possible plant to use for re-vegetating disturbed areas, partly because of its role as a nurse plant. Use in re-vegetation could have a very important ecological impact as a means to reduce invasive plants from entering an area.