Southern Wild Senna

Senna marilandica (formerly Cassia marilandica)

southern_wild_senna_flowers_10-6-14.jpg

Photo of southern wild senna showing a flower cluster and a few leaflets.
Southern wild senna is usually found at the edges of woods, at bases of slopes, in open fields, and in thickets, generally in moist situations.
Family

Fabaceae (beans, peas)

Description

Southern wild senna is an erect perennial, normally with a single unbranched stem. Flowers are yellow and occur in short racemes that arise on stems from the leaf axils. The flowers appear to be regular (not pea flower-shaped) and consist of 5 spreading petals of which 2 are larger than the other 3. Blooms July–August. Leaves are compound with 8–10 pairs of oblong to oblong-elliptic leaflets, to 2 inches long, abruptly tapered to a sharply pointed tip. Fruits are legumes (bean pods), flattened, 2½ to 3½ inches long, dark brown or black at maturity.

Similar species: Missouri’s other two Senna species are weedy, less common, and less widespread. Both produce a disagreeable odor when crushed. Sicklepod (S. obtusifolia) is found mostly in our extreme southeast and southwest counties and sporadically north to St. Louis. It has usually 3 pairs of broadly obovate leaflets. Coffee senna (S. occidentalis) occurs mostly in our southeastern lowlands and has 3–5 pairs of ovate to broadly lanceolate leaflets.

Size

Height: 3–8 feet.

southern_wild_senna_10-6-14.jpg

Photo of southern wild senna showing flower cluster and compound leaves.
Southern Wild Senna
Southern wild senna bears yellow flowers in short racemes. There are 8–10 pairs of oblong to oblong-elliptic leaflets.
Habitat and conservation

Grows on banks of streams and rivers, soughs, bottomland and upland prairies, bottomland forests, rich upland forests, bases, ledges, and tops of bluffs, glades, and savannas; also pastures, old fields, fallow fields, roadsides, and open, disturbed areas. It is sometimes grown as a landscape ornamental.

image of Southern Wild Senna distribution map
Distribution in Missouri

Statewide. Scattered south of the Missouri River; less common farther north.

Human connections

Southern wild senna is sometimes cultivated in gardens as a low-maintenance ornamental for its attractive foliage and flowers and its interesting fruits. Several members of this large genus have been used medicinally or as coffee adulterants; others are pasture weeds implicated in livestock poisoning.

There are about 300 species in genus Senna. These include the sources for cassia gum, a thickening agent in foods, and for neutral henna, a yellow hair dye. Senna leaves have been used as a cathartic or laxative since ancient times. Our word "senna" is virtually unchanged from the Arabic word for these plants. Medieval Europeans looked to Arab doctors for medical knowledge, including the idea of using sweet liquids for taking medicines (which is how we got the words "syrup" and "julep").

Ecosystem connections

Bumblebees pollinate wild sennas.

A wide variety of moth and butterfly larvae eat the leaves, but grazing mammals tend to avoid eating this toxic, cathartic plant.

A small gland at the base of the leaf stalks provides nectar to ants, which apparently protect the leaves from herbivorous insects.