Native to the Western Mediterranean, three-cornered leek is a bulbous perennial with white spring flowers. It’s also known as stinking onion, for reasons which become obvious when close by. In other countries, it’s known as onion grass or onion weed. Part of the allium family, it’s related to edible and ornamental onions as well as cultivated and wild garlic. However, since its introduction to the UK in the mid-18th century, three-corned leek has spread to become an undesirable invasive plant, forming dense colonies and crowding out native plants. It’s an offence to plant or dispose of it in the wild.