Desert Broom (Baccharis sarothroides)
Main sources: Kearney, Thomas & Robert Peebles, et al, 1960, Arizona Flora, pp. 397-99, Berkeley: University of California Press; Shreve, Forrest, 1951, Vegetation of the Sonoran Desert, Washington, D.C.: Carnegie Institute of Washington Publication 591; Dimmit, Mark, "Sunflower family)", in Steven Phillips and Patricia Comus, eds., 2000, A Natural History of the Sonoran Desert, pp. 174-5, Arizona-Sonora Desert Museum Press, Tucson
Like Hymenoclea, Desert Broom is a multi-branched, erect or spreading evergreen shrub with very narrow, linear leaves which persist year-round but may be shed in drought and become more numerous during summer rains. According to Forrest Shreve (cited above, page 71), "The dominant plants of the sandy flood plains throughout the Arizona Upland are Hymenoclea monogyra and Baccharis sarothroides [Desert Broom], both of which are shrubs of rapid growth and of such habit that partial burial by sand does not interfere with their growth." Both appear where periodic flooding over a rather wide floodplain produces occasional deposits of sand. Where sand reaches depths of three feet or more, water infiltration is rapid and the quick drying of surface sands retards water loss, enabling these plants to become established quickly after flash floods. They both then tend to catch silt in subsequent floodings, and contribute to the building of new terraces.
In our area, Desert Broom is much less prominent than is Hymenoclea. While like the latter, Desert Broom is most prominent in our largest streamway, Hot Springs Canyon Wash, Desert Broom is most evident above the Narrows, but becomes quite rare further down, where Hymenoclea becomes quite dense (especially in the 1993 floodplain). For example, see the image below left, taken in January 2003 looking downstream toward the Rabbit Ears Saguaro Hill. Almost all the grayish bushes are hymenoclea, but a single Desert Broom stands out in striking green. (Click on the image to enlarge.) Then, below right, an image taken upstream near Coati Terrace shows again the large grayish bushes, all Hymenoclea, while the small green sprouts along the waterside are all Desert Broom. (Again, click on the image to enlarge.) It might appear that the Desert Broom are migrating downstream.
Desert Broom plants are "dioecious" -- each plant bears only male or female flowers -- and it blooms in the fall (thus extending the flowering season for butterflies and other insects) -- the photos below were taken in November of 2000. The female plants produce white, tasseled seeds in great abundance, and these are dispersed by wind: (Click on images below to enlarge)
For more images of Desert Broom, see this link: San Diego State U. sciences: plants
Desert Broom is relatively short-lived. It is rarely browsed by mammals, but its strong shade fosters the growth of other plants.