Senna marilandica aka American Senna

Senna marilandica lives for many years. It belongs to the pea family, Fabaceae. People call it wild senna or Maryland senna. It comes from the central and eastern United States. Its range runs from Massachusetts and New York to Florida and Texas. It grows in open woods, wet meadows, and disturbed ground. It also grows by rivers, in pastures, and along roads. Plant sellers may still use its old name, Cassia marilandica.

This plant grows fast and stands upright like a shrub. Garden plants reach 4–6 feet [1.22–1.83 metres] tall. Reports give widths of 3–6 feet [0.91–1.83 metres]. Some garden accounts give a narrower spread of 3 feet [0.91 metres]. Its stout, pale green stems have fine hairs near their tops. The dull green leaves grow in an alternate pattern. Each pinnate leaf has pairs of oval leaflets with smooth edges. Sources report four to twelve pairs per leaf. The stems die back to ground level after the growing season.

Yellow flowers grow in groups along the upper stems. Most accounts give July and August as the bloom months. Chicago Botanic Garden says blooms last into October. Each flower has five petals and dark brown stamens. The petals fade toward white as they age. The flowers have no scent and offer pollen, not nectar. Flat seedpods hang down and turn dark brown to black in fall. They stay on the dead stems and add winter interest. Each pod holds ten to eighteen seeds, each in its own section.

Full sun gives the best show of flowers. Part shade also works. Grow it in moist soil that drains well. Rich loam suits it, but sand and clay also work. It copes with heat, humid air, and brief floods. Once plants take root, they can cope with drought. Rich, moist soil can cause tall stems to lean or flop. Published hardiness ranges differ, from USDA zones 4–7 to 4–10. Missouri Botanical Garden lists zones 4–9. It needs little care. Reports list no major pest or disease problems.

Wild senna suits the back of borders and native plant gardens. Bumblebees gather its pollen. Quail and doves eat its seeds. Sulphur butterfly caterpillars eat the leaves and flower buds. Ants, flies, and ladybird beetles visit nectar glands near leaf bases. Plants For A Future lists no known edible uses or hazards. Sources record uses as medicine. These include using leaves and pods as a laxative. Those records do not show that it is a food plant.