Wild indigo (Baptisia tinctoria) is a low shrub-like herbaceous perennial, which grows 2 to 3 feet high and has small (approximately a half inch long) yellow pea-like flowers. The gray-green leaves are somewhat clover-like and trifoliate (divided into three leaflets). Perhaps the most widespread Baptisia species in the eastern United States, it occurs in sandy dry areas, open woods and fields from New England to Florida and west to Minnesota. The flowers bloom July through September and are just now starting to give way to small inflated seed pods. These seed pods are green now, but will turn black when ripe, at which point the seeds will rattle around in the pods giving wild indigo another common name: “rattle weed”. It is also sometimes referred to as “horsefly weed” due to the belief that if the plant was attached to a horse’s harness it would repel horseflies.
The inside of one of the unripe seed pods.
Wild indigo, as the name implies, is related to the tropical indigo plant (Indigofera tinctoria) known for blue dye production. Like I. tinctoria, a blue dye can be rendered from the leaves of our local wild indigo. However, the dye is present only in low concentrations and a large quantity of leaves would be required to obtain reasonable quantities.
In addition to its use as a dye, wild indigo is also an important host plant for many species of butterflies and moths. The dusky-winged butterfly (Thanaos brizo) and Io moth (Automeris io) larvae and caterpillars feed on the leaves. It is also important as a food source for both larvae and adult Frosted Elfin (Callophrys irus). Finally, it is the only known food of the larval stage of the wild indigo dusky winged butterfly (Erynnis baptisiae). In the short time I observed this plant in my yard today, I didn’t see any butterflies, but there was one very industrious bumble bee (Bombus sp.) collecting pollen.