A Guide to Weeds in British Columbia

MARSH PLUME THISTLE DISTRIBUTION

Cirsium palustre (L.) Scop. Family: Asteraceae (Sunflower) Other Scientific Names: None. Other Common Names: Marsh thistle. Legal Status: Regional Noxious: Bulkley-Nechako, Fraser-Fort George.

Growth form: Biennial forb. Stems: Slender, erect stems are usually unbranched Flower: Compact and grow 0.3–2.0 m tall. Stems have spiny wings clusters of purple arising from the winged leaf-bases. flowers form at the tip of Roots: Fibrous. the stems. Bracts at the Seedling: No information available. base of the flowers are sticky and tipped with a Similar Species long spine. Exotics: The prominent spiny wings of the Seeds/Fruit: Seeds are stems separate marsh plume thistle from straw-coloured, 2.5–3.5 mm most thistles (Cirsium sp.). Bull thistle long, with a 9–10 mm long (Cirsium vulgare) is a stout, branched tawny pappus (Douglas et biennial whose leaves bear stout, long al. 1998). spines at the tip of the lobes. Leaves: Spiny basal and stem Natives: No native species have stems leaves are deeply segmented with with spiny wings. prominent woody veins (Cranston et al. 2000). Leaves are lightly to densely hairy on the undersides and have winged bases.

Impacts ______Agricultural: Does not invade cultivated areas but can vegetation, reducing wildlife and livestock forage spread in moist pastures. This unpalatable plant values. Colonizes cut-blocks after harvesting and forms replaces desirable forage plants, thereby reducing dense stands that compete with tree seedlings. Tall, carrying capacity. persistent stems can cause snow press and other forms Ecological: Can colonize undisturbed riparian habitats, of mechanical injury to tree seedlings. moist fields, and meadows, where it may replace native Human: No information available.

Habitat and Ecology ______General requirements: Well adapted to moist-to-wet Distribution: Present in the Cariboo, Vancouver openings, including pastures, bog and fen communities, Island, and Omineca agricultural regions. Most cut-blocks, and roadsides. Grows in a range of soil common in the Robson Valley between McBride and types, including forest floor and even gravel, provided Prince George. seepage is present. Although generally shade-intolerant, Historical: Introduced from Europe. it will germinate under the forest canopy. Life cycle: A biennial that germinates in the first year,

102 A Guide to Weeds in British Columbia overwinters as a rosette, then sets seed and dies the Dispersal: Wind and water disperse the light, following year. parachute-like pappus. Ingestion of seeds by birds may Mode of reproduction: By seed. also disperse seeds. Seed production: No information available. Hybridization: None known. Seed bank: No information available.

Management ______Biocontrol: No specific agents available. A seed-eating weevil (Rhinocyllus conicus) has successfully Integrated Management Summary established on marsh plume thistle in the Robson Valley Forest District and experimental trials are Learn to identify this weed. Early detection is currently underway. important to limit establishment of mature plants, seed banks, and large infestations. On Mechanical: In areas that are suitable for use of small infestations, hand-pull seedlings, mowing equipment, mowing before flowering will rosettes, and mature plants before they set prevent seed-set. seed. Where practical, seed disturbed areas to Fire: Effect not known. perennial grasses and forbs to provide cover Herbicides: Research is required to develop a and competition against this weed. herbicide prescription for this species. Cultural/Preventive: On small infestations, hand-pull seedlings, rosettes, and mature plants before they set seed.

References ______Cranston, R., D. Ralph, and B. Wikeem. 2000. Field Douglas, G. W., G. B. Straley, D. Meidinger, and J. Guide to Noxious and Other Selected Weeds of British Pojar, eds. 1998. Illustrated Flora of British Columbia. Columbia. BC Ministry of Agriculture, Food and Vol. 1: Gymnosperms and Dicotyledons (Aceraceae Fisheries and Ministry of Forests. through Asteraceae). Province of British Columbia.

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