Lesser burdock (Arctium minus)

Synonyms: Lappa minor

Common Names: Common burdock, beggar's buttons, bardane, wild rhubarb, small burdock, wild burdock

Description:

Lesser burdock (Arctium minus) is a large, weedy plant in the aster family, native to Europe and western Asia and now common across North America [1][3]. It grows for two years ? a low cluster of big, heart-shaped leaves the first year, then a tall, branching flower stalk the second [2][3]. MISIN tracks it because it takes over disturbed ground, and because its hooked burs cling to fur, clothing, and feathers ? spreading its seeds and, at times, trapping small birds and bats [4][5].

Habit:

In its first year, lesser burdock is a low rosette (a flat ring of leaves at the base of the plant) of very large, heart-shaped leaves ? some up to 2 feet (60 cm) long ? that are dull green on top and whitish and woolly underneath [2][3]. In its second year it sends up a stout, branched, grooved stalk 2 to 6 feet (0.5 to 1.5 m) tall, topped with round, thistle-like heads of pink to purple flowers from midsummer into fall [2][3][4]. After the flowers fade, each head dries into a round, spiny bur covered in tiny hooks ? the classic "sticky ball" that grabs onto clothing and animal fur [2][4].

The rosettes are easiest to find in spring and early summer on bare, disturbed soil; the flower stalks and burs stand out from July through October [2][3]. By late summer and fall the brown burs are obvious, and they are the surest way to know the plant.

At-a-glance cues:

1. Very large, heart-shaped leaves that are whitish and woolly on the underside [2]
2. A tall (2 to 6 feet), branched, grooved stalk in the second year [3]
3. Round, thistle-like flower heads in pink to purple, midsummer through fall [3]
4. Round, hook-covered burs that cling to clothing and fur [2][4]

Leaves:

1. Arrangement: first-year leaves form a low basal rosette; second-year stem leaves are alternate and get smaller up the stalk [2][3]
2. Shape: heart-shaped to broadly egg-shaped, with coarsely toothed or wavy edges [2][3]
3. Surface: dull green and nearly smooth on top; pale whitish-green and woolly-hairy underneath [2][3]
4. Stalk: long ? up to about 20 inches (50 cm) on the largest leaves ? grooved on top and hollow inside [2][3]
5. Size: the largest basal leaves reach about 1 to 2 feet (30 to 60 cm) long [3][4]

Stems:

1. Habit: upright, stout, and branched, 2 to 6 feet (0.5 to 1.5 m) tall, growing from a deep taproot [3][4]
2. Texture: grooved or slightly ridged, hollow inside, and rough with hairs [2][3]
3. Life cycle: no tall stem the first year ? just a low rosette; the flowering stalk appears in the second year [2][3]

Flowers:

1. Color: pink to purple, sometimes white [2][3]
2. Form: round, thistle-like heads about three-quarters to 1 inch (2 to 2.5 cm) across, made only of tube-shaped florets ? no outer petals [3][4]
3. Arrangement: heads set along the upper branches in long, narrow clusters, growing from the leaf joints and branch tips [3]
4. Bracts: each head is wrapped in stiff green bracts tipped with inward-hooking spines ? these form the bur [3]
5. Bloom time: midsummer through fall, about July to October [2][4]
6. Sex: each flower has both male and female parts [3]

Fruit and seeds:

1. Fruit: a round, dry bur about three-quarters to 1 inch (2 to 2.5 cm) across, covered in stiff, hook-tipped bracts [3][4]
2. Seeds: dark brown, oblong seeds about a quarter inch (5 to 8 mm) long, each topped with short bristles, held inside the bur [3]
3. Amount: one plant makes roughly 6,000 to 17,000 seeds, and an isolated plant can produce up to 30,000 [3]
4. Dispersal: the hooked burs cling to fur, feathers, and clothing and are carried far from the parent plant; burs also float on water or blow across snow [3]
5. Spread: reproduces by seed only ? it has no runners or creeping roots [2][3]

Habitat:

Lesser burdock grows on disturbed, open ground ? roadsides, ditch and stream banks, fence lines, pastures, old fields, vacant lots, and the edges of disturbed woods [3][4]. It is native to Europe and western Asia and is now found in nearly every U.S. state [1][3].

It does best in full to partial sun on moist, rich soils, but it also tolerates poor, dry ground [3][4]. It needs bare, open soil to get started, so it shows up where the ground has been cleared, grazed, or dug [3]. Because young plants grow slowly and often take more than one year to flower, it usually does not last on land that is tilled or disturbed every year [3].

Reproduction:

Lesser burdock spreads in just one way ? by seed ? but it is very good at it [2][3]. Its dry, hooked burs are built to hitch a ride: they cling to animal fur, bird feathers, and your clothes, socks, and shoelaces, so seeds can travel far from where they started [3]. Burs also float on water or blow across the top of snow, moving the plant along streams and into new ground [3]. A single plant produces a lot of seed ? roughly 6,000 to 17,000, and up to 30,000 on a large, isolated plant [3].

The plant lives for two years. Seeds sprout in spring ? in Michigan, most come up around mid-April ? and the plant spends its first year as a low rosette [3]. The second year it shoots up a stalk, flowers from midsummer into fall, and sets its burs [2][3]. This timing is the key to control: pull or cut plants before the second-year burs form and dry, and you stop that year's seeds [3]. Seeds in the soil generally stay alive for less than three years, so a few seasons of stopping seed set can draw a patch down [3].

Impact and Damage:

For homeowners, the biggest nuisance is the burs. They cling stubbornly to clothing, pet fur, and livestock, and handling them can irritate the skin and eyes [4]. On farms, the burs tangle into and lower the value of sheep's wool, and if cattle graze large amounts of the plant it can taint their milk [3]. Lesser burdock is also a secondary host for crop problems such as powdery mildew and root rot, along with certain plant-feeding insects and nematodes (tiny soil worms) [3][4].

In natural and disturbed areas, the plant's huge leaves overtop and shade nearby low-growing plants, holding back native growth and opening bare patches of soil that let burdock and other weeds move in [3]. Its most striking impact is on wildlife: the hooked burs can snag and hold small birds ? hummingbirds, warblers, finches, and wrens ? and bats, which often die of exposure or starvation once they are stuck [5]. Over a 20-year study at Delta Marsh, Manitoba, researchers found 11 hummingbirds and several other songbirds trapped on burdock [5]. These deaths are real but scattered, and the overall effect on bird populations is considered small [3]. Lesser burdock is generally not a serious problem in regularly tilled fields, where cultivation keeps it in check [3].

Similar species:

No look-alikes are currently tracked for lesser burdock in the MISIN region, so these comparisons come from published sources. Its closest matches are two other non-native burdocks.

Greater burdock (Arctium lappa) is larger, with bigger flower heads ? up to about 1.5 inches (4 cm) across ? held in flat-topped clusters on long stalks, while lesser burdock's smaller heads sit in long, narrow clusters on very short stalks or none at all. Greater burdock also has solid leaf stalks, not the hollow ones of lesser burdock [3].

Woolly burdock (Arctium tomentosum) has burs that look almost the same but are wrapped in dense, cobwebby white hairs below the hooked tips, giving them a gray, fuzzy look ? unlike the nearly smooth burs of lesser burdock [3].

Monitoring and rapid response:

Signs to watch for:

1. First-year rosettes: large, heart-shaped, wavy-edged leaves with woolly whitish undersides, lying low on bare, disturbed soil ? roadsides, fence lines, pasture edges, old fields ? easiest to spot spring through early summer [2][3].
2. Second-year plants: tall, branched stalks with pink-purple, thistle-like heads from July into fall, followed by round, hooked burs [2][3].

What you can do:

1. Dig or pull rosettes and young plants, taking as much of the deep taproot as you can ? plants resprout if the taproot is left behind [3]. This is easiest in spring when the soil is moist. Since most seeds sprout around mid-spring, clearing plants before they bolt gets ahead of the next batch [3].
2. For tall, second-year plants, cut or mow before the burs form and dry ? this stops seed set. A plant can still make seed if it is cut after flowering, so cut early and repeat through the season [3]. Bag and remove any seed heads or burs instead of leaving them on the ground [2].
3. Wear gloves and long sleeves ? the burs irritate skin and eyes and stick to clothing [4].
4. Take out isolated plants and small outlying patches first, before they seed ? a single plant can make many thousands of seeds [3]. For a natural area crew: work a site over several visits across the season, focus first on plants near trails and water where burs spread on people and wildlife, and clear burs off clothing and gear before leaving so you don't carry seed to a new site [3][5].
5. Clearing burdock where small birds and bats are active lowers the chance of them getting caught in the burs [5].

When to call a professional:

1. Large or long-established stands, deep-rooted plants in hard or rocky ground that keep resprouting, or infestations along water or roadsides where hand removal is not practical [3].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS PLANTS Database. Arctium minus (Hill) Bernh. plants.usda.gov
2. Michigan State University Plant & Pest Diagnostics. Common burdock ? Arctium minus Bernh. canr.msu.edu
3. Nawrocki T (2010). Arctium minus (Hill) Bernh. ? biology profile. Alaska Center for Conservation Science, University of Alaska Anchorage. accs.uaa.alaska.edu
4. North Carolina Extension Gardener Plant Toolbox. Arctium minus. plants.ces.ncsu.edu
5. Hinam HL, Sealy SG, Underwood TJ (2004). "Ruby-throated Hummingbird, Archilochus colubris, entanglements in burdock, Arctium spp., at Delta Marsh, Manitoba." The Canadian Field-Naturalist 118(1). semanticscholar.org

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