Arctium

The very large, coarse-looking leaves of burdock (blades sometimes half a meter long) might remind one of rhubarb. Each head is dispersed as a bur covered with hooked spines. Both of our species are Eurasian natives, the commoner one, at least, familiar as a weed of disturbed places.

1. Mature heads ca. 2.5–4.5 cm broad (including spines), all or mostly on pedicels ca. 2.4–16 cm long, in terminal, corymbiform inflorescences; phyllaries smooth (at most weakly glandular) on margins and green (except for brownish spine-tips).

A. lappa

1. Mature heads ca. 1.5–2.8 (–3.5) cm broad, all or mostly on pedicels ca. 0.5–3 (–4) cm long, in elongate racemose or paniculiform inflorescences; phyllaries minutely serrulate below the middle and often purplish toward the apex.

A. minus

All species found in Arctium

Arctium lappaGREAT BURDOCK 
Arctium minusCOMMON BURDOCK 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 27, 2017. http://michiganflora.net/genus.aspx?id=Arctium.