Purshia tridentata Bitterbrush

by Kathy Lloyd Montana Native Plant Society

Photo: Drake Barton

Purshia tridentata (Bitterbrush)

honor of Frederick Pursh who used Lewis’s speci- men to describe the species in 1814. In Pursh’s uly 6, 1806 was a busy day for Meriwether book, Flora Americae Septentrionalis, there is a JLewis and his party of explorers. The expe- beautiful hand-colored picture of bitterbrush. Pursh dition was on its way back to St. Louis and had split had given the plant another name, Tigarea triden- into three groups as it crossed Montana headed east- tata, which was later demonstrated to be invalid, so ward. While hurrying across western Montana on to honor him, bitterbrush now carries Pursh’s name. his way to the Marias River, Lewis had time to col- Bitterbrush is a deciduous shrub in the rose family lect plants that were new to him, press them and re- (Rosaceae) and is usually from three to six feet tall, cord botanical notes in his journal. In Ovando Val- but can be much taller in some areas. There are two ley, Lewis collected four plants in what he called the common ecotypes, both present throughout its range. “prairi of the knobs.” The “knobs” are the many There are multiple-stemmed, decumbent plants and small, steep hills visible in the topography of the single-stemmed, columnar plants. The decumbent, area. Lewis may have collected more plants, but or prostrate form is more common at higher eleva- four from that day still survive and are in the Lewis tions. The leaves are wedge-shaped with three & Clark Herbarium at the Academy of Natural Sci- lobes, hence the name tridentata that means three- ences in Philadelphia. toothed. The leaves are green on the upper surface One of the plants collected on July 6 was bitter- and appear to be gray-green on the underside. This brush or Purshia tridentata, as it is known to bota- is due to the presence of dense hairs. Bitterbrush has nists and other plant nerds. The original Lewis a long taproot or taproots that can be as long as 18 specimen, now housed in the Lewis & Clark Herbar- feet, as well as a few shallow roots. The flowers are ium in Philadelphia, has a label by Frederick Pursh yellow and very fragrant, helping to attract the insect that reads, “A Shrub common to the open prairie of pollinators needed to perpetuate the species. The the Knobs. Jul. 6th 1806.” Bitterbrush is named in shrub flowers early, while the leaves are just starting to emerge, and often creates quite a show with bril- shelter in bitterbrush. liant yellow in an otherwise somewhat drab land- Rodents, as well as ants, are important for bitter- scape. In our area, the flowers are gone by mid-June brush regeneration and rodent caches of seeds are and the three-parted leaves are the most distinguish- often crucial to the natural regeneration of bitter- ing feature. The same feature applies to big sage- brush. Rodents and ants may stash the entire crop of brush, Artemisia tridentata, but if you are in doubt seed, some of which sprout. It is a mixed blessing, just take a sniff. Bitterbrush does not have the char- however, since rodents also eat the young plants. acteristic “sage” odor of big sagebrush. Probably of greater concern is competition from Bitterbrush grows from British Columbia to New cheatgrass (Bromus tectorum), a non-native, inva- Mexico and throughout the Rocky Mountains and sive, annual grass that is spreading rapidly in bitter- Great Basin, where it is distributed on over 340 mil- brush and sagebrush habitats. Cheatgrass invasion lion acres. Bitterbrush grows on all slopes and as- has increased the amount of fine fuels in big sage- pects, but is usually found on well-drained soils, brush and bitterbrush grasslands, and bitterbrush is from about 3,000 to 10,000 feet in elevation. Pre- not adapted to the more frequent, high severity fires cipitation usually comes as snow and varies from 12 resulting from increased fuel loads. Some studies to 36 inches annually. Bitterbrush is able to survive have demonstrated that cheatgrass may out-compete on rocky and arid sites because of its long taproot bitterbrush after a fire event. and nitrogen-fixing capacity. Young seedlings can Bitterbrush has been withstand very high surface soil temperatures, which used extensively in land aids their ability to regenerate from seed. Although reclamation and can be bitterbrush is adapted to many harsh conditions, it used on harsh sites does not tolerate saline soils. Look for bitterbrush where it aids in soil re- on dry slopes in the valleys, foothills and montane tention and deposits or- forests. In Montana, bitterbrush is often found on ganic matter. In some south-facing slopes with bluebunch wheatgrass, habitats, bitterbrush Idaho fescue and needle-and-thread grass. It is also fixes nitrogen and in- associated with sagebrush, so don’t forget the sniff creases soil fertility. test. Bitterbrush is a good Bitterbrush also goes by the common name ante- choice for native land- lope brush or antelope bitterbrush. It is an important scapes that encourage browse plant and is favored by deer, pronghorn wildlife use, and re- (antelope), elk, moose, mountain sheep and domestic quires little care once it livestock. Mule deer use of bitterbrush peaks in is established on the Purshia tridentata (Bitterbrush) September, when it may compose 91 percent of the site. Photo: Drake Barton diet. Deer mice and kangaroo rats also use bitter- Traditionally, bitterbrush had many medicinal uses brush, and the seed is a large part of their diets. Be- among Native Americans. An infusion of the root cause it is such a favorite, its vigor is often used to was taken for lung problems and coughs. In Mon- gauge the condition of rangeland. If land is over- tana the dry, ripe fruits were used as an emetic. grazed, the bitterbrush will be severely nibbled and Some tribes chewed the leaves to bring good luck stunted. Domestic sheep may be particularly damag- during hunting. The Shoshone, Sacagawea’s people, ing to bitterbrush since they prefer young and small used bitterbrush as a poultice for skin problems, as a plants. Bitterbrush also supports several insect general tonic, and as a cure for gonorrhea. Others populations. Especially important are Pogonomyr- used the outer seed coat to produce a purple dye mex ants, which stash seeds and are one means by used to stain items made of wood and the Navajo which bitterbrush regenerates, and tent caterpillars, made arrows from bitterbrush wood. which often cause bitterbrush to decline. You may As you begin to notice Montana’s plant heritage, have seen the large tents these caterpillars construct don’t forget the man 200 years ago who first brought in the shrub branches. Birds, rodents and ungulates bitterbrush to the attention of western science, and use bitterbrush for cover. Mule deer and pronghorn remember also the importance of preserving bitter- use bitterbrush stands of different heights for cover, brush habitat and curtailing the introduction and and sage grouse and Lewis’s woodpeckers also find spread of non-native plant species.