w13 Cocklebur

Cocklebur is native to Europe, Asia, southern Canada, and most of the United States, Mexico and Central America. Cocklebur is now found worldwide. Another species that is less common but widespread across North America is called Spiny Cocklebur (X. spinosum).

Cocklebur is an annual, grey-green plant, growing up to 1.5m. The plant’s structure is coarse and bushy with stems that are erect, branched, and rigid, with purple or black spots, and very rough. The leaves are lobed, triangular or heart-shaped, coarsely toothed, borne on long stalks, and rough on both sides. Leaves are 5cm to 35cm long, and 2 to 20cm wide.

Cocklebur flowers from July to October and the seeds ripen from August to October. The flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by insects. The plant is self-fertilising. Male flowers are small and green and hidden at the top of the plant in round clusters. Female flowers occur in burs on short stalks at the base where the leaf axils meet the stem. Each bur contains two flowers. The male flowers drop quickly, while female burs persist, with 2 blackish achenes.

The fruit produced is an elliptic to egg-shaped two-chambered bur, 1 to 3.5cm long, and is covered with about 400 stiff, hooked spines. Two prickles that are longer and wider than the others project from the tip of the bur.

This weed is commonly found in cultivated fields, waste areas, run-down and abandoned pastures, and road ditches. It is poisonous during the two-leafed stage. The burs often become tangled in the fur of grazing animals, thus aiding distribution of the species. Both seeds and seedlings are toxic to livestock.

The seed may be dried, ground into a powder, and mixed with cereal flours during the making of bread and biscuits.

Allergen Description

Cocklebur allergens have not yet been fully characterised. Xan Ib and Xan VIa have been isolated from Cocklebur pollen as the important allergenic components. Xan Ib was found to be devoid of carbohydrate and had a molecular weight of 103 kDa. Xan VIa was a glycoprotein of molecular weight 17 kDa. The carbohydrate moiety of Xan VIa was found to be associated with allergenicity. (1)

Potential Cross Reactivity

Cocklebur is a member of the Ambrosiinae subtribe, tribe Heliantheae, in Asteraceae, as are ragweeds and marshelders. An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Asteraceae. (2) However, despite this close botanical proximity to ragweeds, it was reported that there is little significant cross-reactivity. (3)

However, an earlier study reported that similar antigenic determinants were found between Short Ragweed and Giant Ragweed, Cocklebur, Lamb's Quarters, Rough Pigweed, Marsh Elder, and Goldenrod. Cocklebur and Giant Ragweed were highly potent in their ability to competitively bind to Short Ragweed IgE. (4)

Clinical Experience

IgE mediated reactions

Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are common following exposure to pollen from Cocklebur; however, few specific studies have been reported to date. (5, 6, 7)

In a study in Westchester County in the state of New York of skin prick tests to 48 aeroallergens in100 patients referred for allergic rhinitis, 65% had a positive SPT to at least 1 aeroallergen. Skin prick test for Cocklebur was positive in 3%. (6)

In a study in the Midwestern USA, evaluating the frequency of sensitisation to cannabis pollen, found that 61% were skin prick positive for cannabis and all subjects were also skin test positive to weeds pollinating during the same period: Ragweed, Pigweed, Cocklebur, Russian thistle, Marsh elder, and Kochia. (8)

The incidence of positive intradermal tests after a negative skin prick test for 24 inhalant antigens was conducted on 133 patients in a study in Michigan, USA. Allergens with positive intradermal wheals after negative prick testing included Cocklebur, Rough marshelder, and Ragweed, all with incidences of 16% to 19%. (7)

Common Cocklebur is an important cause of inhalant allergies in Turkey (5) and India. (9)

Other reactions

Cocklebur is a common cause of contact dermatitis. (10, 11, 12, 13)

Last reviewed: June 2022.