IUCN threat status:

Not evaluated

Comprehensive Description

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Description

This native or adventive plant is a summer annual about 2-4' tall and little branched, except for short side stems appearing from the leaf axils. The stems are round or slightly ribbed. They are often speckled with purple and have short white hairs scattered across the surface. The alternate leaves are up to 8" long and 6" across. They are cordate or ovate-cordate with bases that are well-rounded or indented and tips that are broad and blunt. Their margins are shallowly lobed or coarsely toothed, while the upper surface has a sandpapery texture. Each leaf has a long petiole that is often reddish or reddish green and about as long as the leaf blade. The petioles usually have short white hairs. A single spike-like raceme of compound flowers develops from the axil of each upper leaf. These racemes are shorter than the petioles of the leaves, often 1-4" in length. In addition, the central stem terminates in a spike-like raceme that is similar to the racemes of the leaf axils. Because Common Cocklebur is monoecious, each raceme produces several male compound flowers along its upper half, while several female compound flowers occur in the lower half.  The male compound flowers are about ¼" across, consisting of numerous staminate florets that have stamens with prominent white anthers. Each male compound flower occurs on a short pedicel and is slightly rounded at the top, while at the base there are 1-3 series of white floral bracts. After shedding their pollen, the male flowers quickly fade away. The female compound flowers are up to 1½" long and 1" across. Each female compound flower contains 2 pistillate florets, which are nearly enclosed by a prickly floral bract with a bur-like appearance. The female compound flowers are initially green, but turn brown as they mature and are slow to detach from the racemes. They are sessile or have short petioles. The surface of the floral bract is covered with curly white hairs, while the prickles are hooked at their tips. At the apex of each bur, there are a pair of spines that are longer and more stout than the prickles. At the base of each spine, there is a small opening for the divided style of a female flower. These styles are inconspicuous and wither away in a short period of time. The blooming period occurs during the late summer or early fall, although some plants may bloom a little earlier or later. Pollination is by wind and there is no floral scent. Each female flower within the bur-like bract produces a single oblong seed that more or less tapers to a point at each end. The seeds are often covered with dark membranes. One of the seeds in each bur has the capacity to germinate the following year, while the the germination of the second seed is delayed for at least 2 years. The root system consists of a taproot that is stout and rather woody. This plant reproduces by reseeding itself, and often forms colonies. Cultivation

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© John Hilty

Source: Illinois Wildflowers

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