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Xanthium spp.

cockleburs

Asteraceae

The Americas; now worldwide as a weed

Native to North America

SunFull Sun

WaterMedium

Overview

Xanthium spp. is a genus of coarse annual herbs in the daisy family (Asteraceae), native to the Americas and now spread as weeds across temperate and warm regions worldwide. Plants grow 1–5 feet (30–150 cm) tall on rough, branching stems, with large, broad, sandpapery leaves that are lobed or toothed and carried on long stalks. Unlike most of the daisy family, the flower heads are small, green, and without showy rays; separate male and female heads form on the same plant, and the wind carries pollen between them. The female heads harden into woody burs, about 0.5–1.5 inches (1–4 cm) long, covered in hooked spines that catch on fur and clothing and so carry the two seeds inside to new ground. This hitchhiking dispersal has made cockleburs persistent weeds of fields, pastures, and waste places. The seedlings and seeds contain a toxin, carboxyatractyloside, that is poisonous to livestock and people if eaten. Plants complete their cycle in a single season, dying after the burs ripen, and rely entirely on seed to return. Xanthium spp. grows in full sun on disturbed, often damp or seasonally flooded ground.

Native Range

Xanthium spp. is native to the Americas and possibly parts of Asia, and has spread with agriculture to temperate and subtropical regions around the world. Plants grow on disturbed, open ground, including riverbanks, field edges, floodplains, and waste places.

Suggested Uses

Xanthium spp. has no ornamental use and is treated as a weed in most settings. The burs have been studied for their hooked spines, which influenced the design of hook-and-loop fasteners. Some species have a history of use in traditional medicine, despite the toxicity of the seeds and seedlings.

How to Identify

Identify Xanthium spp. by its woody, hook-spined burs about 0.5–1.5 inches (1–4 cm) long, which cling readily to fabric and fur. The large, rough, lobed leaves and coarse upright stems lack the showy flowers of most daisies, the heads being small and green. The burs are the surest identification mark.

Appearance

Size & Dimensions

Height1' - 5'

Width/Spread1' - 3'

Colors

Flower Colors

green

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

Summer Fall

The small green flower heads form in late summer and autumn, with separate male and female heads on the same plant pollinated by wind. There is no petal display. Burs develop after pollination and harden as they ripen, persisting on the dead stems into winter.

Detailed Descriptions

Flower Description

Green, inconspicuous

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 clay sand

Drainageaverage

Water & Climate

Water Needs

Medium

Care & Maintenance

Care Guide

Xanthium spp. is a weed rather than a cultivated plant and grows without care on open, disturbed ground in full sun. It tolerates a wide range of soils, including heavy, compacted, and seasonally flooded ground, and grows across a broad pH range. Seeds can lie dormant in the soil for years and germinate when ground is disturbed, which makes the plant hard to clear once established. Removing young plants before the burs form is the main way to limit its spread. The seedlings are toxic to grazing animals, so the plant is a concern in pastures. Plants die at the end of the season but leave a long-lived seed bank.

Pruning

Xanthium spp. is not pruned, as it is grown by no one and managed only as a weed. Plants are pulled, hoed, or mown before the burs ripen to stop seed forming. Cutting after the burs harden does little, since the seeds can still mature.