One of Mission Trail Regional Park’s most prolific bloomers, broom baccharis (Baccharis sarothroides), also known as desert broom, makes a showy appearance in the fall.

We see a forest of these large bushy plants edging the Visitor Center Trail and throughout the coastal sage scrub habitats. They provide late-year nectar for insects, plentiful ground cover for small animals, and nesting material for birds. They help to stabilize soils and the deep tap root helps to break up hard soil.

When in bloom, close observation reveals it is dioecious (having male and female flowers on separate plants), as the two flowers look quite different.

My observation is that the small male flowers open first.

A member of the Asteraceae (sunflower) family, the male, or staminate, flower heads lack rays but have a cluster of disk flowers that look like many tiny petals surrounding pale yellow pollen on stamens. The females, just prior to opening, look like tiny white paint brushes. Later, the female heads look like fluffy cotton. Pollination is by insects and the wind. The great purple hairstreak butterfly (Atlides halesus) especially favors broom and is frequently seen around the bushes.

Broom baccharis thrives in disturbed and dry soil, is considered a “pioneer” plant (first to fill in vacant land) and is considered invasive near landscaped areas. At maturation the seeds on the female plants are attached to silky fluff making the bushes look like they are covered in feather down. The thousands of tiny seeds are carried on the wind everywhere without regard to anyone’s determination that they stay in one area.

It was interesting to me that I found the most mention of the invasiveness problem on Arizona websites, perhaps it is more of a problem in that state when they attempt to use it as a landscape plant. Removal of a well-established mature plant takes extreme measures. The actively growing plant should be sawn off to stump level and immediately saturated with environmentally safe herbicide so it will filter down the tap root. It is this tenaciousness that gives us our dense broom forests in MTRP.

Broom baccharis is not a plant used extensively by the Kumeyaay for medicinal reasons, but mostly to sweep, as bedding, and as cover on their ‘ewaa if nothing else was available. The Seri indigenous people of Sonora made a decoction by boiling the twigs. The drink or wash was used for colds, aches, and sore muscles. Ongoing, modern studies, on other compounds found in the plant, such as flavonoid, cite minimal effects as cures. Broom baccharis is often blamed for allergies when the seeds fly, but there is no pollen present when the seeds are airborne. Ragweed often blooms at the same time and is more likely the cause.

Enjoy these beautiful blooms while they’re here as they only last about a month.

See if you can find the male and female flowers on separate bushes.

– This article was written by Mary Gibson, a trail guide with Mission Trails Regional Park.