Arctium minus (Common Burdock)
|Also known as:||Lesser Burdock|
|Habitat:||part shade, shade, sun; dry to moist disturbed soil; fields, ditches, open woods, woodland edges, waste areas, railroads|
|Bloom season:||July - September|
|Plant height:||2 to 5 feet|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Small clusters of short-stalked, thistle-like flower heads at branch tips and arising from leaf axils, usually arranged as a tight raceme or panicle. The 20 to 40 disk flowers in each flower head are pinkish-purple to deep purple, occasionally white, with dark purple-tipped stamens surrounding a long white style. Surrounding the base of the flowers is a dense, broadly egg-shaped to round array of softly spiny bracts (phyllaries), the entire set (involucre) 2/3 to about 1½ inches (1.5 to 4 cm) diameter, sometimes variably covered in cobwebby hairs but usually hairless. Each phyllary is lance-linear with a tiny hook at the tip, the edges often minutely serrated especially near the base, less often fringed with minute glandular or non-glandular hairs. Flower stalks are usually less than 1½ inches long but can be 3+ inches.
Leaves and stems:
Leaves are basal and alternate. Basal and the lowest stem leaves are 1 to 2 feet (30 to 60 cm) long, half or more as wide, heart-shaped at the base, rounded to pointed at the tip, on hollow stalks up to 20 inches (50 cm) long. Edges are wavy and toothless or minutely toothed; surfaces are gland-dotted and variably hairy.
Leaves become smaller and shorter stalked as they ascend the stem, becoming stalkless and less wavy up into the flower clusters. Stems are single, usually much branched, stout but brittle, green or reddish purple, hairless to sparsely hairy.
Burdock is a tenacious weed with a massive taproot that does not respond well to herbicide control, plus it has a persistent seed bank. The hooked phyllaries are reputed to be the inspiration for Velcro™. The fruiting heads persist through winter and walking through a patch in early spring can bring you misery. The leaves are similar in size and shape to rhubarb, causing more than a few people to refer to it as wild rhubarb, though I have it on good authority it tastes nothing like it and you'll be sorry you tried it as a substitute. This is very likely in every Minnesota county, though it has not been recorded in several counties. Well, probably...maybe.
For many years I ignored what I assumed was all Arctium minus, since it was the only Arctium species on the DNR's MNTaxa list (still is as of this writing), and the vast majority of herbarium records were for this species, with fewer than 10 records of the related Arctium tomentosum (Woolly Burdock) and Arctium lappa (Great Burdock) combined. I recently checked observations on iNaturalist and was stunned to see hundreds of A. lappa reports, far more than A. minus. As it happens, all three species are conveniently located at a city park near me and I was able to examine and compare them at various stages. I have since concluded that my past encounters were with A. lappa just as often as with A. minus, perhaps even more, though I question whether all those hundreds of reports on iNaturalist are accurate.
Arctium minus tends to be a smaller plant than the other two; those I saw at the local park and elsewhere were not much more than 3 feet tall at maturity, though Flora of North America states it can reach heights of 9+ feet(!) and environmental factors may affect height. Its flower heads are mostly short-stalked and in pretty tight clusters in the leaf axils and at branch tips, where the other two have longer flower stalks that form a more or less flattish cluster. The flower heads are mostly not more than 1 inch diameter, the hooked phyllaries around the flower head may have a few cobwebby hairs and/or a few teeth or short hairs around the edges. In comparison, the flower heads of A. lappa are much larger, well over 1 inch diameter, and plants well over 5 feet tall are common. The phyllaries of A. tomentosum are usually much more densely covered in cobwebby hairs, have minute glandular hairs along the edges, and most plants I've encountered have been 4 to 5 feet tall.
The size and arrangement of flowers plus phyllary characteristics can lead you towards one of these 3, but without flower or fruiting heads it is less straight forward. One other characteristic to check is whether basal and lower leaf stalks are solid or hollow. A. minus has hollow stalks, A. lappa has solid stalks, and A. tomentosum might be either. A. tomentosum leaves are also said to be generally more densely white hairy on the lower surface where the other two are less densely gray-hairy, but I've found any of these can have white or gray hairy leaves at some point so it is not a very reliable characteristic.
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- Common Burdock plant
- Common Burdock plant
- emerging in spring
- flowers are usually short stalked in tight clusters along the stem
- atypical white flowers
- Arctium minus illustration, ca. 1908
- comparison of Arctium minus and A. lappa leaf stalks
- comparison of Arctium minus and A. lappa flower clusters
- comparison of Arctium minus and A. lappa fruiting clusters
- Arctium minus, A. tomentosum and A. lappa flower heads
Photos by K. Chayka taken in Ramsey County.
Have you seen this plant in Minnesota, or have any other comments about it?