Northern Prairie Wildlife Research Center
Tickseed Sunflower (Bidens aristosa)
- Family: Aster (Asteraceae)
- Flowering: August-October.
- Field Marks: Bidens are recognized by their flat fruits with a pair of barbed awns at the tip. Bidens aristosa differs from all other species of the genus with yellow rays by its coarsely toothed or lobed leaflets, its ciliate fruits and the presence of 8-12 outer bracts subtending each head.
- Habitat: Wet meadows, wet prairies, marshes, roadside ditches, cultivated fields, fallow fields.
- Habit: Annual herbs with a taproot.
- Stems: Erect, smooth or slightly hairy, up to 4 feet tall.
- Leaves: Opposite, pinnately divided into 5 or 7 lobes or leaflets, each segment coarsely toothed or lobed, up to 3 inches long, up to 1 inch wide, usually hairy on the lower surface.
- Flowers: Many crowded together into a head, the outer yellow and flat, the inner yellow and tubular, forming a disk, with several heads per plant, each head subtended by 8-12 leafy bracts.
- Sepals: 0.
- Petals: Some yellow, united to form flat rays up to 1 inch long and up to 1/2 inch wide, others yellow, 5-lobed, united below into a tube.
- Stamens: 5.
- Pistils: Ovary inferior.
- Fruits: Achenes flat, ciliate, black or yellow-black, and 1/4 inch long, with two small, stiff barbed awns at the upper end.
- Notes: The fruits of this species adhere to the coats of animals and to clothing and are dispersed in this manner.
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