This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds.
Time of bloom: July to August.
Seed-time: September to October.
Range: New England to Florida, westward to Michigan and
Indiana. Habitat: Moist, open ground; pastures and meadows.
The roots of Wild Senna are spreading, contorted, woody, and black, mostly horizontal, but yet gathering nourishment from the depths through a mass of stringy feeding fibers, also black. With such a food reserve, no wonder it is able to send up yearly such a quantity of growth above ground; for each plant is a collection of many woody stalks, three to six feet tall, erect, slender, pale green, round, smooth, or slightly grooved at base; when young, both stems and leaf-stalks may be slightly hairy. Leaves alternate and set rather far apart, pinnately compound, with five to nine pairs of smooth, oblong leaflets, dark green above and paler below, the edges entire and the midvein extending beyond the rounded tip in a bristly point; petioles short, yellow, grooved on the upper side, and having a prominent, club-shaped gland set just above the swollen base. Flowers bright yellow, springing in many loose clusters from the upper axils; calyx-lobes five, very narrow and reflexed; five unequal petals, three close together at the top, the two below larger and spreading; ten yellow stamens with filaments of differing lengths, tipped with brown anthers of differing sizes, the three lowermost ones largest. Pods about three inches long, flat, curved, slightly constricted between the seeds, hairy when young but becoming smooth as they ripen, and turning to a dark reddish brown. Seeds flat, dark brown, usually four to eight in a pod, possessed of very long vitality when in the soil. A Wild Senna plant in bloom has a look of elegance, as though it cared for its own fine appearance. Grazing animals leave it undisturbed, or if scarcity of forage drive them to browse its leaves they suffer from "scours" as it has a strong cathartic action. It is one of the medicinal plants, and its leaflets, stripped from their stalks at flowering time and carefully dried, may be sold in the drug market for six to eight cents a pound.
If the plants are few they may be grubbed out, but if plentiful this would be a task for Hercules. Cutting close to the ground at the time of bloom, repeating the operation as the roots send up more stalks, will finally exhaust their vitality; but the treatment must be so persistent as to allow no opportunity for storing fresh nutriment. Dry salt on the cut surfaces will help to check new growth; or the plants may be wholly and promptly destroyed by the use of caustic soda or hot brine about the roots, leaving the ground barren for a season.