Allium triquetrum is a bulbous flowering plant in the genus Allium (onions and garlic) native to the Mediterranean basin. It is known in English as three-cornered leek, and in Australia and New Zealand as onion weed. Both the English name and the specific epithet triquetrum refer to the three-cornered shape of the flower stalks.
Allium triquetrum produces stems 17–60 cm tall, which are concavely triangular in cross-section. Each stem produces an umbel inflorescence of 4–19 flowers in January–May in the species’ native environment. Each plant has two or three narrow, linear leaves, each up to 15 cm long. The leaves have a distinct onion smell when crushed.