Flora of New Zealand Series

Californian thistle

Rhizomatous perennial often forming large patches. Stems branched above, with multicellular eglandular and fine cobwebby hairs below, becoming glabrous above, (20)-40-100-(150) cm tall, ribbed, not winged or sometimes with a spiny wing 0-1-(2) cm long decurrent from lf bases. Lvs lanceolate, pinnatifid, green above, pale beneath, (2)-4-15 × 1-5 cm, glabrous or with cobwebby hairs; lobes deltoid to lanceolate; prickles pale, 5-10 mm long. Capitula narrowly ovoid to cylindric at flowering, erect, 1.5-2-(2.5) × 0.7-1.5-(2) cm, in cymes or cymose panicles; peduncles 5-40 mm long. Outer involucral bracts lanceolate, cobwebby-ciliate; apex acuminate, with weak spine 1-(2) mm long, suberect. Inner involucral bracts linear, ciliate; apex acute, not spinous, erect. Corolla usually pale purple or mauve, sometimes white, 12-18 mm long; lobes c. 3 mm long. Style slightly exserted beyond corolla lobes. Achenes pale, cylindric, 3-4 × 1-1.5 mm; pappus 20-25 mm long, shorter in ♂; cilia on pappus bristles 2-3 mm long.

N.: Northland, Auckland, Bay of Plenty, Gisborne, Volcanic Plateau, Taranaki, Manawatu, Wellington; S.: Nelson (Nelson Lakes National Park and Karamea), Marlborough, Canterbury, Otago, Southland, Fiordland; St.

Eurasia 1878

Waste land, roadsides, pastures, cultivated fields, gardens, grassland, sand dunes, occasionally on screes, stony stream banks and tussock grassland to c. 1500 m.

FL Dec-Feb-(Apr) FT Dec-Apr.

C. arvense is almost completely dioecious; ♀ plants do not produce viable pollen, but ♂ plants occasionally set a few seeds. The breeding system of a N.Z. population was described in detail by Lloyd, D. G. and Myall, A. J., Ann. Bot. 40 : 115-123 (1976).

Californian thistle is a widespread and troublesome weed in N.Z. (Plate 1). It is known in many countries as creeping thistle. C. arvense has also been referred to in N.Z. as Carduus arvensis and as Cnicus arvensis.