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 - Yellow, 1/2 in. long or less, usually only 2 or 3 on a long peduncle. Calyx 5-toothed, slightly 2-lipped; corolla papilionaceous. Stem: 3 to 10 in. high, weak, hairy. Leaves: Alternate, simple, oval to lance-shaped; stipules arrow-shaped above and running along stem. Fruit: An inflated oblong pod 1 in. long, blackish, seedy.
Preferred Habitat - Dry, sandy, open situations.
Flowering Season - June - September.
Distribution - New England and Minnesota to the Gulf of Mexico.
These insignificant little yellow flowers attract scant notice from human observers accustomed to associate their generic name with some particularly beautiful relatives from the West Indies grown in hothouses here. But did not small bees alight on the keel and depress it, as in the lupine, next of kin (see p. 22), there might be no seeds to rattle in the dark inflated pods that so delight children. (Krotalon=a Castanet.)