Purshia tridentata has an elevation range from about 1,000-2,700 meters and blooms from about April-July and is thus is a bit more widespread and has a bit longer blooming period than Purshia stansburyana which ranges from about 1,200-2,000 meters and blooms from May-June. The two enjoy the same habitats and do have similar looking flowers and leaves. A close look shows differences: P. stansburyana leaves have three lobes at the apex and one more lobe on each side below the apex; P. tridentata (as its name suggests) has just three lobes, and these are at the apex only. The leaves of P. stansburyana commonly have an odd, quinine-like odor that emanates from the white gland dots on the leaf surface. (Click to see). The seeds of P. stansburyana are borne below long, feathery elongated styles (click to see); the seeds of P. tridentata are encased in pyramid-shaped nutlets and the mature style is neither elongated nor feathery. Seeds of both plants are gathered in large numbers by rodents or the wind and some of these clusters sprout in the spring. Click to see the sprouts. The growth form of the two plants is usually quite different and tells you, even from a distance, which plant you are looking at. Purshia tridentata is most often low, twisted, and spreading; it is typically about six feet wide and three feet high with many horizontal and even prostrate, inter-twining gray stems. Purshia stansburyana can be quite wide but it is more upright, often 5-9 feet tall with more vertical and somewhat arching stems and dark, shredded bark.
Purshia tridentata was first collected by Meriwether Lewis on the Lewis and Clark Expedition, July 6, 1806 near Lewis and Clark Pass, Montana. Frederick Pursh, the first to receive, work on, and publish the Lewis and Clark botanical collections, named the plant Tigarea tridentata in his 1814 publication, Flora Americae Septentrionalis, which included much of the known Lewis and Clark botanical collection. In 1817 the plant genus name was deemed incorrect by the eminent Swiss botanist Augustin Pyramus de Candolle; he created a new genus, Purshia, and renamed the plant, Purshia tridentata. (More biographical information about Pursh.) Purshia stansburyana was at first named Cowania stansburyana by John Torrey in 1852, was renamed Cowania mexicana by Jepson in 1925, went through a number of other name changes, and since 1986 has retained the name Purshia stansburyana given it by Henrickson. |
As shown at left, the two shrubs do hybridize; leaves may have the characteristic smell and white scale of P. stansburyana, the hairiness of P. tridentata, and a mix of the leaf shape, height, and width of the two.
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Species present in state and native
Species present in state and exotic
Species not present in state
Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Eradicated
Questionable presence
