Spanish needle

Bidens bipinnata

This plant is a summer annual about 2-5' tall; it is more or less erect and branches occasionally. The stems are green or reddish green, angular, strongly veined, and hairless (or nearly so). The leaves are mostly opposite; their blades are up to 8" long and 4" across, while their petioles are up to 2" long. The leaf blades are double- or triple-pinnate, medium green, and hairless (or nearly so). The segments of the blades are ovate, lanceolate, or oblanceolate with blunt tips and wedge-shaped bottoms; the margins of these segments are irregularly cleft or dentate. Overall, the leaf blades have a fern-like appearance. The upper stems terminate in individual flowerheads on long peduncles. Each flowerhead is about ½" long and ¼" across; it has numerous disk florets in the center and 0-5 ray florets along its upper margin. The disk florets have corollas that are golden yellow and tubular in shape; each corolla has 5 tiny lobes along its upper rim. The yellow ray florets are petal-like; they are about 1/8" (3 mm.) long and oval to oblong in shape. Some flowerheads may lack petal-like extensions of the ray florets altogether. The base of the flowerhead is surrounded by green bracts; the linear inner bracts are much longer (about 1/3" or 8 mm. in length) than the outer bracts. The blooming period occurs during the late summer or early fall. Each flowerhead is replaced by a seedhead that is globoid in shape and spans about 1" across. The long narrow seeds (achenes) spread outward from the center in all directions. Each mature seed is linear in shape, 4-angled, and dark brown; it has 2-4 short awns at its tip. Each tiny awn has downward-pointed barbs. The root system consists of a branching taproot. This plant spreads by reseeding itself.

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