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Description

This herbaceous plant is a biennial or short-lived perennial; it is about 1-2' tall, branching occasionally. The stems are glabrous and light green; they are terete or somewhat angular. The alternate leaves are usually trifoliate, although some of the smaller upper leaves are simple. The lower leaves often appear to be palmate with 5 leaflets, but this is because each lateral leaflet has been deeply divided into 2 large lobes. In outline, the lower compound leaves are nearly orbicular in outline (up to 5" wide and 5" across, excluding the petioles) while the upper compound leaves are more narrow. The leaflets and large lobes are obovate, ovate, or broadly elliptic in shape, while their margins are coarsely double-serrated and sometimes cleft along their margins. Leaf venation within each leaflet and lobe is pinnate. The upper leaf surface is yellowish green (in bright sunlight) to dark green (in shade) and glabrous. The lower leaves have long petioles, while those of the upper leaves are much shorter. These petioles are light green, glabrous, and slightly sheathed at their bases; they are grooved above and convex below. The upper stems terminate in small umbels or compound umbels of greenish white flowers. Each umbel consists of 1-4 umbellets and spans up to 2½" across. Each umbellet has 2-3 pistillate or perfect flowers and about 2-6 staminate flowers (less often, there will be 7-15 staminate flowers); these flowers form a tight cluster that is irregularly globular in shape. The perfect and pistillate flowers are more conspicous because of their bur-like ovaries. These ovaries are about 3-5 mm. in length, globoid-ovoid in shape, and green; their outer surfaces are covered with hooked prickles (about 1 mm. in length). Each flower has 5 greenish white petals and a green calyx with 5 linear-lanceolate lobes; these lobes are shorter than the prickles of the ovaries. The styles of perfect and pistillate flowers (less than 1 mm. in length) are also shorter than the prickles of the ovaries. Each staminate or perfect flower has 5 short stamens. The blooming period occurs from late spring to mid-summer and lasts about 3 weeks for a colony of plants. There is no noticeable floral scent. Each bur-like fruit contains 2 seeds. The root system is fibrous. This plant spreads by reseeding itself and it occasionally forms colonies.

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

© John Hilty

Source: Illinois Wildflowers

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