1a. ssp. arvensis

Branches of the inflorescence moderately to densely pubescent with spreading, gland-tipped hairs toward the tip, rarely also sparsely to moderately pubescent with minute, branched, cobwebby hairs. Involucre with a central stripe of moderate to dense, spreading, gland-tipped hairs, rarely also sparsely to moderately pubescent with minute, branched, cobwebby hairs toward the base. 2n=54. July–October.

Introduced, uncommon, known only from the city of St. Louis (native of Europe, introduced widely in North America). Gardens.

Plants of ssp. arvensis tend to differ from those of ssp. uliginosus in being overall somewhat more robust, with slightly larger lower leaves and slightly larger heads, but the differences are not so marked that they can be circumscribed easily in a key. Steyermark (1963) reported this subspecies from Jackson County, but no specimens could be located during the present study to confirm its presence there. The St. Louis occurrence is based on a single historical collection from the grounds of the Missouri Botanical Garden.