C. maculosa of Michigan Flora.

A Eurasian invader first collected in 1911 in an alfalfa field at Hesperia (on the Oceana/Newaygo Co. line); no collector is recorded. Now spread aggressively everywhere: old fields on poor soil, roadsides, disturbed sites, and disturbed places, especially in the northern part of the state, where it takes over open sites.

Our plants are subsp. micranthos (Gugler) Hayek, sometimes called C. biebersteinii DC. Since the introduction of C. diffusa, these two species seem to have hybridized extensively in some areas, blurring the distinctions in the key.