Alismataceae

Non-woody (herbaceous) aquatic or wetland plants with 3 green sepals and 3 white or pink petals, 6 to many stamens and carpels that are arranged in rings or spirals and not fused, and basal leaves that are often expanded and arrow- or lance-shaped when they project above the water; Arrowheads and Water-plantains. Can be difficult to identify due to considerable variation in leaf shape, often on the same plant, related to environmental conditions.

Flowers and branches bearing white or pink flowers in racemes or panicles near the top of a flower stalk. Individual flowers usually symmetrical in all directions (radially), and somewhat resemble those of buttercups. Pollen-producing structures and seed-producing structures may be on the same flower, or separate flowers on the same plant. Ovaries located above site of attachment of other flower parts (superior), stigma 1 per carpel, tiny. Nectar-bearing structures may be present at the bases of any of the flower parts. Fruit a dense head-like cluster of achenes, rarely capsules. Fruit and fresh flowers often needed for accurate identification.

Simple basal leaves with smooth edges and parallel veins or veins all arising at the base of the expanded portion of the leaf blade. Submerged leaf blades often narrower than those that are above water or floating; leaves above water or floating often arrow- or lance-shaped. Leaf bases or the stalks of expanded leaves often wrap around stem at their bases (sheathing). Stipules absent, hairs usually also absent.

Plants produce white latex, and often have spongy tissue with air spaces.

A small family widely distributed in temperate and tropical waters, with greatest diversity in the Western Hemisphere.