Partridge Pea is an annual and usually only noticed along the path edges as it does not grow over 2 1/2 feet high and young plants can be as short as 4 inches with a single flower as some of the photos below indicate. The stem often branches making the plant as wide as it is tall, which causes larger plants to sprawl. Stems are green and smooth, except young stems may have fine hair.
Leaves are pinnately compound with 8-15 pairs of unstalked leaflets, each entire, lance shaped and tipped with a sharp bristle. The leaf has a pair of awl shaped stipules at the base of its stalk and on the stalk is a small gland, either sessile or with a very short stalk. Leaves are sensitive to daylight and fold the leaflets toward each other with darkness.
Flowers occur from the leaf axils, not terminal stems, sometimes 2 to 4 together, on long slender stalks, quite showy, up to 1 1/2 inches wide with 5 bright yellow petals that are about equal size. Three to four however have red at the base. With the petals spreading open, unlike the typical pea family flower, the reproductive parts are visible. There are ten stamens of unequal length with purple anthers on 6, yellow on 4. The style is greenish-white. Beneath the petals are 5 green linear sepals from a very short calyx.
Seed: Fertile flowers mature into a flat straight pod that is green and slightly hairy, turning dark brown and smooth at maturity at which time they split with a twisting action which can fling the seeds away from the plant. Seeds are heavy for such a small plant - about 250 to the ounce. They require at least 10 days of cold stratification for germination plus scarification and a legume inoculum helps. Otherwise plant in the fall without any treatment and let nature do the work.
Toxic: See bottom of page.
Habitat: Partridge Pea requires full to partial sun and drier upland sites. It is invasive if not controlled and toxic to animals.
Names: Partridge Pea was formerly classified in the genus Cassia, as one of the Sennas where it was named Cassia chamaecrista L. The older name of Sensitive Pea is based on the leaflets being sensitive to daylight as explained above. The genus name, Chamaecrista (and the former species name) is now used for plants that have sensitive leaves and pods that suddenly split to eject the seed. The word is from two Greek words - chamae, meaning 'low growth' and crista for 'crested'. The species, fasciculata, refers to a bundle of nerve fibers, referencing the sensitiveness of the leaflets.
The author names for the plant classification are : While no longer in the classification chain, the first to tackle the species was Linnaeus in 1753. His work was revised by ‘Michx.’ which refers to Andre Michaux (1746-1802), French botanist who made many exploring expeditions in the U.S. collecting and cataloging many species. Two important works were the Histoire des chênes de l'Amérique septentrionale (1801 - Oaks of North America), and the Flora Boreali-Americana (2 vols., 1803, published posthumously) In this last work was his classification of Partridge Pea. Both Michaux and Linnaeus assigned the name Cassia chamaecrista. Michaux's son Francois, traveled with him and the father’s notes were later used for the 3-volume North American Sylva. Michaux's work on this species was updated by ‘Greene’ in 1897, arriving at the current name. This was Edward Lee Greene (1843-1915), American botanist who wrote Landmarks of Botanical History, named or re-described over 4,400 species of plants in the American west and was the first Professor of Botany at the University of California.
Above: A plant showing the arrangement of leaves and flowers rising from the leaf axils. Drawing by William Curtis.
Below: 1st photo The flat seed pods, this example from very late August. 2nd photo - Flowers: Note the red at the base of the petals.
Below: 1st photo - The long leaf showing the paired leaflets. Note the bristly tips. 2nd photo - Note the small reddish leaf stalk gland and the pair of awl shaped stipules at the base of the stalk.
Notes: Eloise Butler first noted Partridge Pea's presence in the Garden when she saw the blooms in 1911. She reports planting seeds on Sept. 10, 1913 and 20 plants on Aug. 3, 1914, more plants in Sept. 1918, '24, and '32; seeds in '26 & '27. Martha Crone sowed seeds in 1945, '48, '53, and the plant was listed on her 1951 inventory of plants in the Garden at that time. Partridge Pea is native to certain counties of Minnesota along the Mississippi River from the Metro area south and also along the south side of the Minnesota River and several adjacent counties. This is the limit of its northern exposure. In the U. S. it ranges from the central plains eastward. Not known in Canada. It is considered weedy in certain states as it can become invasive in pastures and open areas.
Eloise Butler wrote of this plant: "The beauty of the large flower of clear, bright yellow is enhanced by a purplish brown eye formed by the stamens and the blotching of some of the petals. The delicate, fresh, green leaflets of the compound leaf close together when touched and also for protection from cold at night." Published Aug. 13, 1911 in the Minneapolis Sunday Tribune.
Toxicity and Use: Partridge Pea is the bane of pastures. George (Ref.# 6b) reports that Partridge Pea is strongly cathartic to browsing mammals, causing sickness, not only with fresh plants but with winter fodder that had Partridge Pea growing with it when harvested and stored. Mrs. Grieve (Ref.#7) reports that leaves and seeds of this plant can be used for medicinal purposes much like the those Sennas of the genus this plant was formerly assigned to.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"