Allium triquetrum bulb cornwall England Enlgish flowers Great Britain natural nature petals spring three-cornered leek white wild boulders cliff clifftop coastline Cornish english granite granitic hard headland hillside ocean plants rocks sea shore tide view water waves aggressive-grower allium-triquetrum Amaryllidaceae blooming blooms bulbous-flowering-plant edible fast-spreading flower-stalks flowering garden green introduced invasive leaves Mediterranean-import onion-weed profusion snowbell stalks three-cornered-leek bay bluebells Hyacinthoides non-scriptum inlet