Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Genus: Xanthium
Species: X. spinosum
Binomial name: Xanthium spinosum
Synonyms: Xanthium spinosum var. ambrosioides, Xanthium spinosum var. heterocephalum, Xanthium spinosum var. inermeBe
Common names: Bathurst burr, Spiny cocklebur, Prickly burweed,
Xanthium spinosum is a species of flowering plant in the aster family. It is known worldwide as a noxious weed of pastures, croplands, waterways, grasslands, waste areas, roadsides and disturbed sites. It is native to parts of South America. In New Zealand, it is found growing in fertile soils of the northern and eastern areas of the North Island. It is found in only a few scattered areas in the South Island.
Xanthium spinosum is an erect, much branched annual herb producing a slender stem up to 1-2 metre tall. It is lined at intervals with very long, sharp, straight, yellowish spines which may exceed three centimetres in length and may divide into two or three separate spines
The alternately arranged leaves (>12 cm long and >30 mm wide) and are borne on stalks (petioles) up to 30 mm long. The lower leaves are usually irregularly three-lobed, or occasionally with five lobes, with the middle lobe much larger than the others. However, on upper leaves the side lobes may be insignificant or absent, thereby giving the leaf blade an elongated (lanceolate) shape. The leaf upper surfaces are dark green and shiny with prominent whitish-coloured veins, while their undersides are pale green or whitish in colour with a dense covering of downy hairs.
The plant produces small, creamy green male and female flower heads in December, January, February, March, April. The female heads developing into burs one or 1.5 centimetres long and covered in thin spines. The burs contain two seeds, one which germinates the first year, and the second the next year. The spiny burs are easily dispersed to new areas when they become attached to animals, clothing and vehicles, and objects, or float along watercourses, or in contaminated agricultural produce. Plants die off in early winter after producing burs.
Bur damage to sheep's wool reduces its value and they also break shearing combs. The plant’s spines damage the feet of stock. The plants, especially new seedlings, are toxic to livestock.
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