5. Alismataceae - Arrowhead; marsh and aquatic herbs; leaves basal, erect or floating, petiole long, bases sheathing, blades linear to sagitate or hastate; flowers perfect or imperfect (monoecious or dioecious), in racemes or panicles; sepals 3, separate, green; petals 3, separate, often white; stamens 6 to many; carpels 6 to many, unilocular, one ovule per locule; fruit an achene.