Flower:

Racemes of 1 to 4 pea-shaped flowers on branching stems in the upper plant, alternating with and opposite to the leaves. Flowers are about 1/3 inch long, yellow, with a broad, nearly round erect petal at the top (the standard) that is barely notched at the tip, and 2 shorter lateral petals extending out over the green keel. The calyx holding the flower is short-stalked, 5-pronged, the prongs as long as or longer than the petals, and covered in long white hairs. Only a few flowers may be open at a time.

Leaves and stems:

Leaves are 1 to 3 inches long, to 2/3 inch wide, lance to elliptic, toothless, covered in long white hairs on both surfaces, rounded to pointed at the tip, stalkless or short-stalked. Stems are erect and branching, densely hairy, green to purplish. Where the raceme stalk meets the stem is a joined pair of leafy appendages (stipule) about ½ inch long, extending down the stem and each side 1-pronged at the tip.

Fruit:

Fruit is an inflated, oblong pod to 1¼ inch long at maturity, initially light green, ripening to purplish black.

Notes:

Rattlebox is not commonly encountered, only present in a few Minnesota counties as we are on the northern fringe of its natural range. It is listed as a Special Concern species in Wisconsin and was designated as such in Minnesota in 2013 due to its low populations and the dwindling prairie and savanna habitats this species calls home.