Arctium

1	Petiole of basal leaves solid throughout; capitula diam. 3-5 cm; most peduncles 3-10 cm long Arctium lappa
1'	Petiole of basal leaves hollow at least near base; capitula diam. 1.5-2.5(-3) cm; most peduncles sessile or up to 3 cm long Arctium minus