Rayless Marigold (Bidens frondosa)
Also known as Beggar-Ticks or Sticktight. It looks like a big single marigold from which someone has plucked off all the rays. As with Spanish Needles, the hooked seeds stick to animal fur or clothing. The species is variable, and Gray notes that it hybridizes even across genera. This plant grew at the edge of an alley in the South Side flats.
From Gray’s Manual: B. Frondosa, L. (COMMON BEGGAR-TICKS, STICK-TIGHT.) Smooth or rather hairy, tall (2-6° high), branching; leaves 3-5 divided; leaflets mostly stalked, lanceolate, pointed, coarsely toothed; outer involucre much longer than the head, ciliate below; achenes wedge-shaped, 2-awned, ciliate (the bristles ascending except near the summit). —Moist waste places; a coarse troublesome weed, the achenes, as in the other species, adhering to clothing, etc., by their retrorsely barbed awns. Hybrids occur with Coreopsis aristosa and other species. July-Oct.