This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
5 petals, 3 forming an upper lip, 2 a lower one; 10 stamens of 3 different kinds; 1 pistil. Stem: 3 to 8 ft. high, little branched. Leaves: Alternate, pinnately compounded of 6 to 10 pairs of oblong leaflets. Fruit: A narrow, flat curving pod, 3 to 4 in. long.
Preferred Habitat - Alluvial or moist, rich soil, swamps, roadsides.
Flowering Season - July - August.
Distribution - New England, westward to Nebraska, south to the Gulf States.
Whoever has seen certain Long Island roadsides bordered with wild senna, the brilliant flower clusters contrasted with the deep green of the beautiful foliage, knows that no effect produced by art along the drives of public park or private garden can match these country lanes in simple charm. Bumblebees, buzzing about the blossoms, may be observed "milking" the anthers just as they do those of the partridge pea. No red spots on any of these petals guide the visitors, as in the previous species, however; for do not the three small, dark stamens, which are reduced to mere scales, answer every purpose as pathfinders here? The stigma, turned sometimes to the right, sometimes to the left, strikes the bee on the side; the senna being what Delpino, the Italian botanist, calls a pleurotribe flower.
While leaves of certain African and East Indian species of senna are most valued for their medicinal properties, those of this plant are largely collected in the Middle and Southern States as a substitute. Caterpillars of several sulphur butterflies, which live exclusively on cassia foliage, appear to feel no evil effects from overdoses.