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.
Flowers - Bright lavender blue, showy, about 2 in. long; from 1 to 3 borne on a short peduncle. Calyx tubular, 5-toothed; corolla butterfly-shaped, consisting of very large, erect standard petal, notched at rounded apex; 2 oblong, curved wings, and shorter, acute keel; 10stamens; style incurved, and hairy along inner side. Stem: Smooth, ascending or partly twining, 1 to 3 ft. high. Leaves: Compounded of 3 oblong leaflets, paler beneath, each on short stalk. Fruit: A few-seeded, acutely pointed pod about 1 in. long.
Preferred Habitat - Dry soil.
Flowering Season - June - July.
Distribution - New Jersey to Florida, westward to Missouri, Texas, and Mexico.
A beautiful blossom, flaunting a large banner out of all proportion to the size of its other parts, that it may arrest the attention of its benefactors the bees. According to Henderson, the plant, which is found in our Southern States and over the Mexican border, grows also in the Khasia Mountains of India, but in no intervening place. Several members of the tropic-loving genus, that produce large, highly colored flowers, have been introduced to American hothouses; but the blue butterfly pea is our only native representative. The genus is thought to take its name from kleio, to shut up, in reference to the habit these peas have of seeding long before the flower drops off.