rough cocklebur | skymeadows

TAXONOMY: The taxonomy of Xanthium strumarium is complex and can be confusing (as indicated by the large number of synonyms listed above). The Plants Database includes the following three varieties of Xanthium strumarium: 1) Xanthium strumarium L. var. canadense (Mill.) Torr. & A. Gray, 2) Xanthium strumarium L. var. glabratum (DC.) Cronquist, and 3) Xanthium strumarium L. var. strumarium.

Two varieties, var. canadense and var. glabratum, occur in Virginia, but have not been distinguished previously on herbarium specimens. Var. canadense is said to be more frequent on the Atlantic coast than inland. The treatment here follows FNA in not recognizing varieties, a practical solution for inherently variable, weedy species. The original range of this cosmopolitan species is now obscure, but it is probably native to our area.

NATIVE STATUS: Native, United States and Canada.

GENERAL BOTANICAL CHARACTERISTICS:

Habit: Rough cocklebur is a summer annual that that ranges in height from 2-4' tall. It is little branched, except for short side stems developing 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.

Leaves: 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.

Flowers: 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.

Fruits/Seeds: 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 two years.

Common cocklebur may also set seed without fertilization of the ovule. Because of self-compatibility and apomixis, local populations are often
genetically very similar. A single, open-grown plant typically produces
400 to 500 fruits.

Roots: The root system consists of a taproot that is stout and rather woody.

REGENERATION PROCESS: Rough cocklebur reproduces by reseeding, Pollination is by wind; rough cocklebur often forms colonies.

The fruits can also cling to the hide of animals. In riparian habitats, fruits on the soil surface may later betransported by animals fall from the plant during the fall or winterclothing of humans and can be dispersed in that manner. Fruits not dispersed by water as they float for up to 30 days. The fruit does not dehisce, and thus seeds germinate within the fruit.

HABITAT TYPES: Rough cocklebur occurs primarily in disturbed, open habitats often with, poorly drained areas. It grows in cultivated fields (especially corn fields), fallow fields, vacant lots, sandpits, and dry washes; degraded meadows that are poorly drained; dried-up mudholes; on beaches and sand dunes (it primarily occupies beaches and dunes in eastern North America and floodplains in the West); the floodplain zone of rivers and ponds, especially riverbeds left barren by receding floodwaters.

Habitat density of rough cocklebur various - in ruderal habitats,

such as agricultural fields, rough cocklebur often occurs in dense
stands, but in natural habitats, such as along shorelines, it often
occurs as scattered individuals.

SITE CHARACTERISTICS: Rough cocklebur prefers full or partial sun, moist to mesic soil, and loamy or sandy soil. Occasional flooding is tolerated if it is not too prolonged and it is tolerant of flooding at all growth stages. Rough cocklebur is tolerant of a variety of soil conditions ranging from moist clay to dry sand but grows best on compact sandy soil that is slightly moist below the soil surface and contains a small amount of organic matter.

SEASONAL DEVELOPMENT: Rough cocklebur typically blooms during the late summer or early fall, although some plants may bloom a little earlier or later.

GENERAL DISTRIBUTION: Rough cocklebur is very widely distributed, ranging throughout all the continuous states and Canadian
provinces of North American, excepting Newfoundland and the northern
Canadian provinces.

SKY MEADOWS DISTRIBUTION: To be determined.

IMPORTANCE AND USES: The flowerheads rely on the wind, rather than insects, to cross-pollinate individual plants. Insects that feed on common cocklebur include the ragweed leaf beetle (Ophraella communa), stem-boring larvae of the sunflower longhorn beetle (Dectes texanus), stem-boring larvae of the sunflower stem weevil (Cylindrocopturus adspersus), five-spotted billbug (Rhodobaenus quinquepunctatus), Thirteen-spotted billbug (Rhodobaenus tredecimpunctatus), stem-boring larvae of several tumbling flower beetles (Mordellistena spp.), larvae of leaf-miner flies (Calycomyza platyptera, Liriomyza trifolii), larvae of the bur-seed fly (Euaresta aequalis), spotted green plant bug (Ilnacora stalii), a leaf-feeding aphid (Capitophorus xanthii), stem-boring larvae of the ragweed borer moth (Epiblema strenuana), and seed-eating larvae of a moth, the pale-headed phaneta (Phaneta ochrocephala). The seedlings and seeds of common cocklebur are highly toxic to mammalian herbivores, including cattle, horses, sheep, and pigs. The foliage of more mature plants is less toxic, although the fatal poisoning of calves has been reported from its consumption. When cattle and horses feed on mature plants with burry fruits and flowers, this can cause obstruction of the gastrointestinal tract if they are eaten in sufficient quantity. White-tailed deer occasionally chomp off the upper half of mature plants before the bur-like flowers develop. Because the burry fruits readily cling to the fur of mammals and the clothing of humans, they are easily transported to new areas, spreading the seeds of this plant. Even though the seeds are regarded as highly toxic, there are records of their consumption by the Franklin ground squirrel, prairie deer mouse, and purple finch.

In the United States, rough cocklebur is a major weed in cotton and
soybean fields. Infestations in soybean fields can cause severe crop
losses, as much as 60 to 75 percent. Rough cocklebur is effectively

controlled by a number of soil- or foliar-applied systemic herbicides commonly used in agricultural fields.

Rough cocklebur is considered a nuisance by livestock producers. The
plant grows in barnyards, pastures, and around farm ponds where it is
commonly encountered by livestock. The spine-covered burs become
entangled in the hides of farm animals. Wool value is decreased if
entangled with rough cocklebur.

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