Flower:

There are 1 to 3 stalked flower heads at the ends of branching stems. The flower center is round, ¼ to ½ inch across, orange-yellow, made up of tiny disk flowers with 4 or 5 lobes. Ray flowers (petals) are uncommon, though 1 to 5 yellow rays, often short and stubby, may be observed.

Inner bracts surrounding the disk are all equal in size, narrowly egg-shaped, brownish green to yellow. The outer leafy green bracts are unequal in size, 2 to 3 times longer than the head, narrow lance-elliptic to spatula shaped, loosely and irregularly spaced, usually with a few short hairs scattered around the edges.

Leaves and stem:

Leaves are 1½ to 4 inches long, 1/3 to 1¼ inches wide, opposite, mostly unlobed, lance-elliptic with serrated edges or irregularly toothed, a sharp point at the tip, stalkless or tapering at the base to a short winged stalk, hairless or hairy to varying degrees, especially around the edges.

Sometimes lower leaves have one to a few deep lobes towards the base. Stems are erect and can be green or tinged red but usually purple in color, hence the common name Purple-stem Beggarticks. Stems are typically smooth but fine hairs may be present.

Fruit:

The flower heads produce purplish black to brown seeds ¼ to 1/3 inch long that are 4-angled but somewhat flattened. At the top are usually 2 to 4 barbed awns that help it attach to anything that passes by (like my clothes). Barbs are along the angles and often the surface as well.

Notes:

There are several species of Bidens with similar flowers, but they are not so difficult to tell apart once you know the secret.The flowers of Devil's Beggarticks (Bidens frondosa) are most similar, but it has leaves compound in 3s or 5s, and seed with only 2 awns. Three-lobed Beggarticks (Bidens tripartita) also has opposite leaves that are mostly simple, but a broader flower head that is yellow, not orangish, larger, more numerous leafy bracts, and seeds that are mostly all 3-awned. Big Devil's Beggarticks (Bidens vulgata) has 10 to 20 densely hairy leafy bracts around a 1-inch disk.