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This plant is a summer annual about ¾-2½' tall that branches occasionally. The stems are light green, terete, stellate-pubescent, and spiny. The sharp spines are 4-10 mm. long., yellow, and straight. Alternate leaves occur along these stems that are 1-3½" (2.5-9 cm.) long and ¾-3" (2-7.5 cm.) across. These leaves are deeply pinnatifid with obtuse lobes that sometimes develop smaller secondary lobes; their margins are toothless and very undulate (both horizontally and vertically). These lobes are irregularly shaped, although they tend to be obovate or broadly oblong. The upper leaf surface is medium green and mostly glabrous, except for scattered short hairs, while the lower leaf surface is pale green and stellate-pubescent. Along the central vein of the lower leaf surface, there are often scattered spines that resemble those along the stems. The petioles are ½-3" long, mostly pale green, and stellate-pubescent; their upper sides are flat to slightly concave, while their lower sides are convex. The lower sides of the petioles also have spines that resemble those along the stems. Sometimes the lower petioles become pale reddish purple with age. The upper stems terminate in short racemes of flowers. There are about 3-10 flowers per raceme, although some flowers may abort. Each flower is about 1" (2.5 cm.) across, consisting of yellow corolla with 5 ovate-triangular lobes, a short-tubular green calyx with 5 linear-lanceolate teeth, 5 stamens, and a pistil with a single style. Both the body and lobes of the calyx are stellate-pubescent; the body of the calyx, which encloses the ovary, is also densely covered with spines that resemble those of the stems and other parts of this plant. The stamens are dimorphic


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© John Hilty

Source: Illinois Wildflowers

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