Maltese centaury

Centaurea melitensis is an erect annual or biennial herb of the daisy family growing 20-100 cm tall with a slender taproot and a stiff, sparingly branched, narrowly winged stem covered with a sparse cobwebby pubescence. Basal leaves are oblanceolate, 5-15 cm long, often pinnately lobed and withered by flowering time; cauline leaves are smaller, lanceolate, entire to slightly toothed, and decurrent down the stem to form conspicuous narrow wings. Inflorescences are small, solitary or clustered capitula 1-2 cm across at the tips of the branches; ray florets are absent, and the disc florets are bright yellow, slender, and tubular. The involucral bracts are armed with stout palmately-radiate spines, the central spine 6-12 mm long and considerably longer than the laterals, a feature that distinguishes the species. Achenes are small, pale, finely striped, and crowned with a short white pappus. A native of the Mediterranean naturalised throughout western North America and elsewhere as a weed, it flowers May to August.