Ambrosia dumosa

Ambrosia dumosa
Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Asterales
Family:	Asteraceae
Genus:	Ambrosia
Species:	A. dumosa
Binomial name
Ambrosia dumosa (A.Gray) W.W.Payne

Burro weed, or Ambrosia dumosa, is a common constituent of the creosote-bush scrub community throughout the deserts of the American Southwest. Ambrosia dumosa has been studied to determine allelopathic interactions with creosote bush, Larrea tridentata, which produces a chemical that inhibits the growth of A. dumosa. Other studies have suggested that A. dumosa roots prduce a chemical that causes them to grow away from conspecific roots, preventing competition for water resources.

Morphology

A highly branched shrub 2 to 9 dm in height. The branch stems are covered with soft gray-white hairs and have compound mostly obvate leaves that are 1 to 3 pinnate and generally clustered on the short branches. The leaves are 0.5 to 4 cm wide and also covered in soft gray-white hairs.

Its infloresence is yellow with staminate and pistallate heads (monoecious). Staminate heads have many flowers and are 3 to 5 mm in diameter with a 5 to 8 lobed involucre. Pistallate heads are 2 flowered and lack corolla.

A. dumosa has spherical fruits ranging in color from golden to purple to brown. Along with microscopic hairs, the fruit has 12 to 35 flat and straight spines which are 5 to 9 mm in length and scattered over the surface.

It has been noted that the wind blown pollen is often highly allergenic.

References

• Jepson Manual Treatment: Ambrosia dumosa
• Schoenerr, Allen A. (1992). A Natural History of California. Berkeley: University of California Press. ISBN 0-520-06922-6