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Crotalaria spectabilis

showy rattlebox

Overview

Crotalaria spectabilis is an erect annual legume in the pea family, growing 3-6 feet (0.9-1.8 m) tall and 1-2 feet (30-60 cm) wide on stout, branching stems. The simple, oval to oblong leaves are 2-6 inches (5-15 cm) long, blue-green above and paler beneath. From mid summer into autumn it bears upright terminal racemes 6-16 inches (15-40 cm) long of yellow pea-shaped flowers, each about 0.75-1 inch (2-2.5 cm) long. The flowers give way to inflated, cylindrical pods 1.5-2 inches (4-5 cm) long that turn black and rattle as the loose seeds dry inside, the source of the common name rattlebox. Native to tropical Asia, it was introduced to the southeastern United States as a cover and green-manure crop and has naturalized widely in fields, roadsides, and disturbed ground, where it is now treated as an agricultural weed. All parts, especially the seeds, contain pyrrolizidine alkaloids including monocrotaline, which are toxic to livestock, poultry, and humans and can cause cumulative liver damage. It grows quickly in warm weather and sandy soil, tolerating heat and drought, but it is killed by frost and completes its cycle in one season. It is listed as a noxious or invasive plant in several southeastern states.

Native Range

Crotalaria spectabilis is native to tropical Asia, including the Indian subcontinent and Southeast Asia. It was introduced to North America and has naturalized across the southeastern United States in fields, roadsides, pastures, and other disturbed, sunny ground.

Suggested Uses

Crotalaria spectabilis has been grown as a soil-building cover crop and green manure in warm regions, where its nitrogen-fixing roots and fast summer growth suit rough ground. Its toxicity to livestock and weedy spread limit its use in pastures and managed landscapes. It is grown only where its self-sowing can be controlled.

How to Identify

Look for a tall, erect annual with stout stems and simple blue-green oval leaves 2-6 inches (5-15 cm) long. Upright racemes of yellow pea flowers about 0.75-1 inch (2-2.5 cm) long appear from summer into autumn, followed by inflated black pods 1.5-2 inches (4-5 cm) long whose loose seeds rattle when shaken. The simple, undivided leaves and inflated rattling pods separate it from other yellow-flowered legumes.

Appearance

Size & Dimensions

Height3' - 6'

Width/Spread1' - 2'

Colors

Flower Colors

yellow

Foliage Colors

green

Bloom Information

Bloom Period

~10 weeks

Summer Fall

Yellow pea-shaped flowers open from mid summer into autumn, roughly July to October in warm climates. Each raceme blooms from the base upward over several weeks. Flowering continues until frost ends the season.

Detailed Descriptions

Foliage Description

Blue-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 - 7.0(Neutral)

357912

Soil Types

sand loam

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Crotalaria spectabilis grows in full sun in well-drained sandy or loamy soil with a pH from about 5.5 to 7.0. As a warm-season annual it germinates in spring and grows quickly through summer heat, tolerating poor soil and drought once established. It needs no fertilizer because, like other legumes, it fixes nitrogen through root nodules. The plant self-sows freely and can spread into surrounding ground, which has made it an agricultural weed across the warm Southeast. All parts contain pyrrolizidine alkaloids that are toxic if eaten. Frost kills the plant at the end of the season.

Pruning

Crotalaria spectabilis needs no pruning as an annual. Removing the seedpods before they ripen limits self-sowing and spread into surrounding ground. Plants are pulled or cut down at the end of the season.