Getting a handle on broom: Scotch, French, and Spanish brooms in California

Scotch broom (Cytisus scoparius), French broom (Genista monspessulana), and Spanish broom (Spartium junceum) were introduced to California in the mid-1800s for landscape planting, mine tailings stabilization, and roadside erosion control.

Traits once considered useful are the very attributes that define brooms as an aggressive and invasive noxious weed today. Brooms are invasive due to their tolerance for most soil conditions, their ability to fix nitrogen and grow for most of the year, and their copious production of long-lasting viable seeds. These practical attributes for erosion control also make the plants difficult to manage.

Broom grows rapidly and so densely that wildlife find passage difficult. It is slightly toxic and rarely browsed by wildlife or livestock. The dense stems make regeneration of most other species impossible and create a dangerous fire hazard. As the plants grow, the inner stems die back providing a highly flammable fuel.

The California State Department of Food and Agriculture (CDFA) has declared broom a Class ³C² pest species--³troublesome, aggressive, intrusive, detrimental or destructive to agriculture, silviculture, or important native species, and difficult to control or eradicate.²

Scotch broom identification

Scotch broom is an upright evergreen shrub that can grow to 12 feet tall but is more commonly 3 to 6 feet high. It reproduces by seeds that germinate mainly in spring and autumn. Young plants usually do not flower until their third year. Plants live up to 25 years, although 10-15 years is more usual.

Scotch broom stems--are numerous, erect, woody, green to brownish green, prominently ridged, and have five distinct angles. Young stems remain green for about three years and actively photosynthesize.

Scotch broom leaves--are found singly or in clusters, on short stalks, with scattered hairs above and soft hairs below the bright green groups of three leaflets. Single leaflets can be found on the growing tips. Each leaflet is oval to lance-shaped, 1/16--5/16" wide. The central leaflet is largest, up to 3/4" long. New leaves, produced in spring, are often lost during dry periods in summer or other periods of stress. Plants may be leafless for most of the year.

Scotch broom flowers--are pea-like, bright yellow, sometimes with red markings in the center on short stalks. They are singular, about 1/2--1" long. April to June is the peak flowering time but some flowers may appear sporadically throughout the year.

Scotch broom fruits--are flat, brown or black pods. They are green when immature and hairy on the edges, mostly 1--2-1/2" long and 5/16--1/2" wide. Seed pods ripen during summer and burst open to eject the seed. Some pods curl up after seed is ejected.

The seeds are green to yellowish-brown when ripe. There are 5 to 20 shiny, rounded and flattened seeds 1/8 inches long and 1/16 inches wide per pea-like pod.

French and Spanish broom identification

French and Spanish broom look very similar to Scotch broom at first glance. The plants are about the same size, color, and have similar appearance to the flowers and stems.

French broom has obvious trifoliate leaves. Leaflets are largely oval and about 1/4" long. Leaflets appear waxy above, and slightly hairy below. Spanish broom will often appear nearly leafless especially later in the season.

However, the flowers of both French and Spanish broom are found in clusters. Spanish broom flowers are noticeably fragrant while French broom flowers have a subtle fragrance. French broom stems are ridged but not sharply angled. Spanish broom has round stems.

Uses

Not surprising given the name, brooms have been used historically for sweeping. They have also been used for thatching, fence rows, and cattle fodder. The leaves, bark, and flowers have been gathered for their medicinal properties. The flowers have been used as a hops substitute in beer and the seeds as a coffee substitute. The woody plant was used for tanning leather and very large old stems for veneer. The fiber can be made into cloth.

In the next issue of Forestland Steward, we will discuss the ecology and management of the brooms.

A new publication on brooms, written by John LeBlanc, Getting a Handle on Broom (ANR Publication 8049), is now available for download.