Onopordum acanthium L.
cotton thistle
Taprooted biennial. Stems branched above, covered with dense, white felted tomentum, 1-3 m tall, with broad dentate spiny wings 5-18 mm wide. Lvs deltoid to ovate to lanceolate, shallowly pinnatifid, coarsely dentate, grey-green, 20-30 × 15-20 cm, with dense fine felted tomentum above and beneath; prickles marginal, yellowish, spreading, 5-10 mm long. Capitula broadly ovoid, waisted at flowering, erect, 2-4-(5) × 2-4-(5) cm, solitary; peduncles elongating just before anthesis, 5-15-(25) cm long. Involucral bracts linear-subulate, 2-3 mm wide at base, the outer and middle with dense cobwebby tomentum; apex spinous, spreading to suberect. Corolla purple or white, 20-24 mm long; lobes unequal, 5-7 mm long. Style exserted 3-4 mm beyond corolla lobes. Achenes dark, narrowly obovoid to clavate, weakly transversely flattened and 4-angled, rugose, 5-6 × 2-2.5 mm; ribs 4, pale; pappus bristles scabrid, 5-10 mm long.
N.: Wellington (Thorndon); S.: Marlborough (Spring Creek), Canterbury, Otago.
Europe, W. and C. Asia 1880
Waste land, pastures, roadsides, riverbeds, shingle and ballast.
FL Dec-Feb FT Jan-Mar.
O. acanthium is often known as Scotch or heraldic thistle in Britain; in N.Z. the name Scotch thistle is always applied to Cirsium vulgare.
