Scientific Family
Fabaceae
Synonyms
Crotalaria chiapensis, C. lupulina, C. triantha
Other common names
rattlebox
rattlesnake weed
Plant type
Forbs and Subshrubs
Origin
Native
Lifecycle
Annual or perennial
Height
To nearly 2 feet
Riparian
No
Small shrub with minutely hairy to smooth stems; green leaves are divided into 3 narrow leaflets that are smooth above with flat, fine hairs below. Clusters of dainty butterfly-like yellow flowers at times tinged with red grow on stalks up to 1 foot long.
Subshrub; erect-ascending from a taproot; leaves trifoliate, leaflets oblong, without hairs above, appressed hairs below; flowers yellow, short-stemmed have a banner, wings and keel and in many-flowered elongated clusters; fruit an inflated oblong pod.
Habitat
Sandy, gravelly or clayey soils on flats, along the margins of washes and roadsides.
Plant Community
Pinyon Juniper Woodlands
Interior Chaparral
Grasslands
Disturbed Areas
Low elevation
4000
High elevation
6000
Flower Characteristics
Each yellow flower has 5 petals. A large petal at the top (banner), a pair of petals below the banner (wings) and between the wings are 2 fused petals (keel). The banner and keel may be streaked with red. The tip of the keel extends beyond the wings.
Flower color
Yellow, may be tinged with red
Flower shape
Irregular
Tubular
Yes
First bloom month
June
Last bloom month
October
Flower clusters
Elongated
Leaf and Stem Characteristics
Stems are smooth or slightly hairy. Compound leaves have a distinctive shape made up of 3 leaflets (trifoliate). Leaflets are oblong, 1/8 to 3/4 inch wide and 2-1/2 inches long, smooth above with a slight whitish waxy coating and flat, fine hairs below.
Leaf type
Compound
Leaf color
Bright green
Leaf shape
Narrow
Leaf margin
Smooth
Leaves clasp
No
Leaf hairs
Leaves & stems
Spines
No
Fruit and Seed Characteristics
Pods are round to oblong shaped, 1/4 to 1/2 inch wide, 1/2 to 3/4 inch long, plump and bladder-like with straight, stiff, sharp, flat hairs and a slender tip. When shaken, the dry brown seedpods make a rattling sound like that of a rattlesnake's tail.
Fruit type
Pod
Fruit color
Green, brown with age
Seeds are yellow to reddish-brown, kidney-shaped, about 1/8 inch long and smooth. When fully dry, the seedpods will suddenly explode open with an audible pop and eject the seeds a fair distance from the plant in a process called "explosive dehiscence".