Common waterplantain  (Alisma plantago-aquatica)

Common waterplantain, a perennial aquatic broadleaf plant, can behave as an annual in California rice and wild rice fields. It is found throughout California, except in the Mojave and low deserts (Sonoran) and the Great Basin region up to 5200 feet (1600 m). Common waterplantain grows in shallow water and exposed mud in and around wetlands, streams, rice and wild rice fields, and ponds. It is particularly a problem in rice fields where the stand is sparse and cold water enters. Although seeds are the most common source of new plants, plants are able to regenerate from the bulbous base, creating problems where fields have been inadequately plowed. Beneficial to wildlife, common waterplantain is usually only considered a weed in controlled aquatic systems and rice fields.

Habitat

Wetlands, streams, rice and wild rice fields, and ponds.

Seedling

Cotyledons (seed leaves) are football to lance shaped, about 2-1/2 to 3 times as long as broad, with long stalks that are often reddish-tinged. They usually float on the water surface. Immature leaves are bladeless or have very reduced blades. Seedlings may be confused with upright burhead because their cotyledons also float on the water. However, young burhead plants are usually covered with water and have stalkless leaves, whereas seedling waterplantain leaves are stalked.

Mature plant

Mature common waterplantain grows in clumps with most leaves rising above the water surface and some floating. Leafless flowering stems grow to about 4 feet (1.2 m), extending well above the leaf blades that can grow to over 1-1/2 feet (0.5 m) tall. Leaves are variable in shape, from lance to egg shaped. Leaf blades are about 2 to 8 inches (5–20 cm) long and have parallel main veins and transverse tiny veinlets.

Flowers

Flowers bloom from June through July. The flowering stem is much taller than the leaves and has four or more whorls of flowers that attach at the stem joints (nodes). Beneath each node are 2 to 3 papery, leaflike structures (bracts). Flowers have three white (rarely pink) petals with rounded tips and smooth or jagged edges. Three to ten flowers comprise a whorl.

Fruits

The fruiting head consists of a dense ring of one-seeded fruit (achenes). Achenes are strongly compressed, longer than wide, have rounded backs, and a short beak on the opposite side.

Reproduction

Reproduces mostly by seed, but to a limited extent reproduce from side shoots.

Related or similar plants

• Upright burhead, Echinodorus berteroi

More information

• Broadleaf ID illustration
• Calflora's distribution map
• For agriculture: UC IPM Pest Management Guidelines