WEEKLY LETHAL WEED PROFILE: NODDING THISTLE

A NODDING THISTLE

Alternative Name(s): Carduus nutans subsp. leiophyllus, Musk Thistle.
Family: Asteraceae.

Form: Herb

Origin: Native of Europe and western Asia.

Flowers/Seedhead: Many small flowers (florets) in solitary heads at ends of branches; florets 20–35 mm long. Flowers spring and summer.

Description: Erect biennial thistle to 2.5 m high. Leaves variable, basal leaves in a rosette, green and often with white midveins, 5–40 cm long, 2–7.5 cm wide, earliest leaves not as deeply lobed, later basal leaves as well as stem leaves deeply dissected.

Distinguishing features: Distinguished by spiny winged stems (except just below flower heads) and spiny leaves; leaves hairless or sparsely hairy above and below; bracts around heads hairless, 4–8 mm wide near base, spine-tipped, outer ones reflexed, inner ones spreading to erect; mature heads 2–8 cm wide (including bracts) and erect to slightly nodding; all florets tubular, purple, arising from a hairy receptacle; seeds 4–6 mm long, hairless, topped by numerous simple white bristles (pappus) 15–25 mm long.

Dispersal: Spread by movement of seed.

Confused With: Carduus nutans another nodding thistle with bracts around heads having some hairs and 1.5–3 mm wide near base, and obviously nodding heads.

Notes: First recorded in Queensland near Gympie, but has spread from this area. Only known from Queensland. It appears to grow in warmer areas than C. nutans in Australia. A pasture weed in some areas of south-eastern Queensland and a serious pasture weed in North America.

 

References: Flora of south-eastern Queensland. T. Stanley and E. Ross, Vol. 2, 1986, page 581. The Biology of Australian Weeds. R. Groves et al. (eds), Vol. 1, 1995, pages 29–49.

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