Insect activity around the blossoms of an unimpressive, spreading, woody shrub caught my attention in mid-October. Small shrubs were scattered on the flood plain while larger plants were common along the edges of the wash and around seeps. The shrub, native to the Southwest, is known as desert broom (Baccharis sarothroides). It also goes by broom baccharis, desertbroom, Mexican broom, greasewood, rosin-bush and groundsel. In Spanish, it is called “romerillo”, “escoba amarga” and “hierba del pasmo”.
B. sarothroides is deciduous and loses its leaves with summer droughts and winter frosts. All the plants observed had lost their foliage, leaving photosynthesis to be conducted by highly branching green twigs and branches. The plants growing along the wash edges were lush with flowers at the ends of most terminals and led to a discovery. The species is dioecious with male and female flowers on separate plants. The flowers of both sexes were small, unspectacular and appeared to lack petals. The male flower buds were slightly larger and more rounded with a pale yellow-green color (Photo 1a) while the female flowers were white (Photo 1b).
Photo 1a: Close-up of male flowers
Photo 1b: Close-up of female flowers.
I was first attracted to B. sarothroides by the plethora of insect species associated with the flowers. After repeated visits, I got the impression that the diversity of insects working the male flowers was greater than those attracted to the female flowers. Moths, butterflies, beetles, bees, wasps, and flies were actively feeding on the male flowers while the female flower feeders were primarily bees and wasps.
By the end of October, the male flowers had senesced and begun to take on a dull brown color. At the same time, female plants were opening their flowers to expose tiny mature fruits, called achenes, with short gossamer threads attached. The threads help disperse the seeds in even the slightest of breezes in what is called ballooning (Photo 2and 3).
Photo 2: A female B. sarothroides plant with mature fruits ready for distribution by the wind.
Photo 3: A close-up of a single B. sarothroides achene showing the gossamer threads.
The region’s Native Americans bound desert broom twigs together to make brooms and used the plant for preparing a wide range of remedies. Pharmacological studies have shown it to contain phytochemicals with anti-inflammatory, antioxidant, and cholesterol lowering qualities. The woody branches of the desert broom were used as arrow shafts.
Desert broom has been used in the past in landscaping but due to its high pollen count and its proliferation and distribution of seeds, it is currently in disfavor.
For additional information on desert broom, conduct a web search using the scientific name Baccharis sarothroides.
