Crotalaria spectabilis (Showy Rattlebox)

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Crotalaria spp.

rattlepods

Fabaceae

Pantropical; centre of diversity in sub-Saharan Africa

Attracts Pollinators Drought Tolerant

Native to North America

SunFull Sun

WaterLow · drought-tolerant

HardinessZones 9–12

Overview

Crotalaria spp. is a genus of roughly 700 species of herbaceous plants and shrubs in the legume family (Fabaceae), distributed across tropical and subtropical regions worldwide, with the greatest concentration in Africa. Plants range from 1–10 feet (0.3–3 m) in height, with simple or trifoliate leaves and upright to spreading stems. Flowers are pea-shaped, 0.4–1 inch (1–2.5 cm) long, and borne in terminal racemes; most species are yellow, sometimes marked with brown or purple veining. The common name rattlepod refers to the inflated, papery seed pods, 1–2 inches (2.5–5 cm) long, in which loosened seeds rattle when the dried pod is shaken. Several species, including C. juncea (sunn hemp), are grown as green-manure and cover crops because they fix atmospheric nitrogen through root nodules. All parts contain pyrrolizidine alkaloids that are toxic to livestock and humans when ingested, causing cumulative liver damage; this limits the use of most species near grazing animals. Foliage is typically mid-green and herbaceous, dying back in species from seasonal climates. Most members require full sun and well-drained soil and tolerate low fertility, though species native to wetter regions need consistent moisture. The genus spans short-lived annuals, herbaceous perennials, and woody shrubs, so growth form and longevity vary considerably between species.

Native Range

The genus is pantropical, with its centre of diversity in sub-Saharan Africa and additional species native to tropical Asia, Australia, and the Americas. Crotalaria spp. occupies grasslands, savannas, and disturbed ground from sea level to montane elevations.

Suggested Uses

Crotalaria spp. species are grown as green-manure and nitrogen-fixing cover crops in rotation systems, particularly C. juncea. Some shrubby species are planted in tropical and subtropical borders for their yellow racemes. The genus is also used in soil-stabilisation and revegetation plantings on degraded ground.

How to Identify

Identify Crotalaria spp. by its pea-shaped yellow flowers in terminal racemes and the inflated, bladder-like seed pods 1–2 inches (2.5–5 cm) long that rattle when dry. Leaves are simple or divided into three leaflets and arranged alternately along the stems. Stems are often ribbed and covered in short appressed hairs.

Appearance

Size & Dimensions

Height1' - 10'

Width/Spread1' - 5'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Most species flower through the warm season, from late spring into autumn in subtropical climates and across much of the year in the tropics. Individual racemes open progressively from the base upward over several weeks. Pollination is carried out chiefly by bees, after which the rattling seed pods develop and dry on the plant.

Detailed Descriptions

Flower Description

Yellow, sometimes marked brown or purple

Foliage Description

Green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

loam sand

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

tender

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Grow Crotalaria spp. in full sun and well-drained soil of low to moderate fertility; most species tolerate sandy, nutrient-poor ground because of their nitrogen-fixing nodules. Water needs are low to moderate, with species from seasonally dry regions tolerating drought once established and those from wetter habitats needing steadier moisture. In regions where plants are grown as annual cover crops, seed is sown after the last frost. Plants grow rapidly in warm conditions and may be cut and turned into the soil before flowering when used as green manure. All parts are toxic if eaten, so the genus is kept away from pasture intended for livestock. In frost-prone areas, tender species are killed by cold and treated as annuals.

Pruning

Cover-crop species are mown or cut to the ground before seed set and turned into the soil. Shrubby perennial species can be cut back after flowering to keep a compact form and remove the spent pods. Annual species need no pruning and are cleared at the end of the season.