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Xanthium strumarium

rough cocklebur

Asteraceae Americas (origin uncertain)

Deer Resistant

Native to North America

SunFull Sun

WaterMedium

Overview

Xanthium strumarium is a coarse summer annual reaching 1.5-4 feet (0.5-1.2 m) tall, occasionally to 6 feet (1.8 m), with a stout, often purple-spotted branching stem. Leaves are alternate, broadly triangular to heart-shaped, 2-6 inches (5-15 cm) long, with toothed or shallowly lobed margins and a rough, sandpapery surface on both sides. The plant is monoecious: small greenish male flower heads cluster at the branch tips above clusters of female heads in the leaf axils. Female heads develop into hard, woody burs 0.5-1.5 inches (1.3-3.8 cm) long, covered in hooked prickles and tipped with two beaks, each bur holding two seeds. The burs cling to fur and clothing and float on water, carrying the seed far from the parent. Seedlings and seeds contain carboxyatractyloside and are toxic to livestock, particularly pigs and cattle, when eaten in quantity. Plants die at first frost, leaving the burs on dry stems through winter. Germination occurs over an extended period, so seedlings appear from spring into summer.

Native Range

Of uncertain origin, most likely native to the Americas, now naturalized on every continent except Antarctica. Grows in disturbed soils along riverbanks, floodplains, agricultural fields, and roadsides from sea level to about 5,500 feet (1,675 m).

Suggested Uses

Not cultivated; it occurs as an agricultural and floodplain weed. The mature burs are sometimes collected for dried arrangements. It has no managed garden use and is regarded as a weed across its range.

How to Identify

Identified by triangular, sandpapery leaves on long stalks and hard, two-beaked burs 0.5-1.5 inches (1.3-3.8 cm) long covered in hooked prickles. The stem is often spotted or streaked with purple. Distinguished from Xanthium spinosum by the absence of three-pronged yellow spines at the leaf bases.

Appearance

Size & Dimensions

Height1'6" - 4'

Width/Spread1' - 3'

Colors

Flower Colors

green

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~12 weeks

Summer Fall

Flowers from July through October, triggered by shortening day length. Wind-pollinated male heads shed pollen for 2-4 weeks above the inconspicuous female heads. Burs mature in fall and persist on dead stems into the following spring.

Detailed Descriptions

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

clay loam sand silt

Drainagemoist

Water & Climate

Water Needs

Medium

Care & Maintenance

Care Guide

Grows as a summer annual in full sun on moist, fertile, disturbed soils and tolerates periodic flooding. Seeds germinate across a wide range of conditions, with the two seeds in each bur often sprouting in different years, which spreads emergence over time. No cultivation is practiced; in crops and pastures it is controlled by removing plants before the burs harden. The toxic seedlings are most hazardous to livestock at the two-leaf stage. Plants are killed by the first hard frost.

Pruning

Not pruned in the ornamental sense. Removing plants before the burs mature limits both seed dispersal and the buildup of long-lived seed in the soil. Cut plants regrow weakly from the base where soil moisture stays high.