Seven species of arrowheads (Sagittaria) are recorded for Missouri, and all are emergent aquatic plants growing on muddy banks or in shallow water. All but one (an annual) are perennials having either rhizomes, corms (sometimes inaccurately called tubers), and/or stolons (runners). The leaves are basal; the leaf stalks have sheathing bases. The leaf blades that emerge above water vary in shape but are most typically arrowhead-shaped or halberd-shaped, with well-developed basal lobes. Other species have oval, lance-shaped, or narrow, grasslike leaves. The main veins arch from the base of the blade and rejoin at the leaf tip; these veins are connected by finer, angled veins running parallel to one another. Submerged leaf blades are often grasslike or lance-shaped.
The flowers are arranged in whorls on the overall flowering stalk. In many cases, the flowers are unisexual: either male (staminate) or female (pistillate). In these cases, the male flowers are more showy, with 3 white petals and 3 green sepals, and many stamens; the female flowers are usually lower on the stalk, below the male flowers, and resemble green globes with bracts at the base. These nubbins are receptacles that hold a cluster of many densely packed pistils that mature to become flattened, usually wing-edged seeds that are ribbed on the sides.
Of our seven species, three typically have the characteristic arrowhead or halberd-shaped leaves, with large basal lobes, and occur nearly statewide:
- Midwestern arrowhead (or short-beaked arrowhead, S. brevirostra) is one of our common species and is scattered nearly statewide; perennial. It can be distinguished by its large leaf blades and by the bracts at the base of each whorl of flowers, which are ¾–2½ inches long, linear to lanceolate, with a narrowly acute tip. Also, the female flowers are on stalks ½–1½ inches long. Blooms June–September.
- Common arrowhead (or broadleaf arrowhead, S. latifolia) is scattered statewide, more common south of the Missouri River; perennial. A species much used historically for its fairly large, edible corms, it is the one most likely to be called duck potato or wapato. The achenes (seeds) have beaks that spread at a right angle to the body of the achene (not pointing upward). The nodes of the flower clusters have boat-shaped bracts to about ½ inch long, fairly rounded at the tip. Blooms June–October.
- Mississippi or hooded arrowhead (S. calycina, syn. S. montevidensis ssp. calycina) is scattered nearly statewide; it’s the only annual arrowhead in our state. Also unlike our other arrowheads, the flowers comprising the lower whorl of flowers are perfect, having stamens as well as the nubbin-like receptacle formed by a dense cluster of pistils. These perfect flowers are on short, very thickened stalks that curve downward. The white petals have yellow at the base. Sometimes the leaves are lance-shaped and unlobed. Blooms June–September.
Four of our species have leaves that are not arrowhead or halberd-shaped; two of them are uncommon and have limited distributions:
- Sessile-fruited arrowhead (S. rigida) is scattered in Missouri, most commonly in the Ozarks, absent from the southeastern lowlands; perennial. The lower, female flowers, and the fruits that develop from them, are stalkless (sessile); the overall flower stalk bends abruptly at the lowest whorl of flowers. Leaf blades are grasslike to oval, sometimes with a pair of small lobes at the base or arrow-shaped. Blooms May–October.
- Narrow-leaved arrowhead (or lance-leaved, grass-leaved, or grassy arrowhead, S. graminea) is scattered statewide, mostly south of the Missouri River; usually perennial. True to its many names, its leaves are narrow and grasslike. The leaflike bracts attached at the nodes of the flower stalks are fused only in the basal half, with the free portions triangular with an acute tip. Blooms May–September.
- Kansas arrowhead (or plains sagittaria, S. ambigua) is uncommon in southwestern Missouri; perennial. Its leaves are lance-shaped or oval. The filaments of the stamens are glabrous (not roughened) and are not swollen at the base. The leaflike bracts attached at the nodes of the flower stalks are fused only at the base, with the free portions narrow and grasslike to lance-shaped, with an acute tip. Blooms June–August.
- Delta arrowhead (S. platyphylla) is uncommon in the Mississippi Lowlands of the Bootheel, plus one disconnected occurrence in Boone County; perennial. Its leaves are lance-shaped or oval. In this species, as the lower, female flowers develop into globe-shaped clusters of fruits, their stalks thicken and bend downward. The leaflike bracts attached at the nodes of the flower stalks are fused most of their length, with the free portions broadly triangular. Blooms May–August.
Similar species: Water plantains (Alisma spp.) and burheads (Echinodorus) are in the same family, and they have three-petaled flowers that look like tiny versions of arrowhead’s flowers. Water plantains look like gigantic versions of the plantains that commonly appear unwanted in yards. They bear large, elaborately branching stalks of tiny, white, three-petaled flowers. Burheads have clusters of beaked seeds that develop in the fall. Hundreds of these spiny seed heads, held in clusters above the water, make them distinctive.
Leaf length (including the stem): only to about 15 or 20 inches in the smaller species; up to 60 inches in the larger ones.
Distribution varies with species; see descriptions above.
Habitat and Conservation
Arrowheads are emergent aquatic plants that grow along muddy margins of ponds, ditches, sloughs, sluggish streams, and similar habitats. Some species live in marshes, fens, and other wetlands. Some species will flower in dried mud.
Some species, such as Sagittaria latifolia, are commonly used in pond restorations, rain gardens, and other aquatic uses where they can be naturalized. They can be quite ornamental. The flowers are showy, the leaves are interesting, and water birds eat the seeds. They spread by rhizomes and from seeds. Deadhead the spend flowers to prevent unwanted spread from seeds.
The starchy corms (potato-like “tubers”) of some arrowhead species have been baked, roasted, boiled, and even candied. Different species may produce corms of different sizes. Large-leaved species might develop larger corms than species with smaller leaves.
Native Americans valued some arrowhead species for food, drying the corms to eat in winter.
To harvest the corms, you can’t just yank on the plant stalk; it tends to just break off. Historically, Native Americans waded into the water and used their feet and toes to squish around in the muck and release the corms, which float up to the surface. You could try using a rake. The corms are not positioned directly below where the plants are emerging from the water. They develop in a circle in the muck, at varying depths, around where the plants appear to be.
Most people report that uncooked duck potatoes, though edible, are not very tasty. Boiling or roasting them for about half an hour seems to be the trick. Remove the stalk, first, and then peel them after cooking.
The young stalks, tender, uncurling leaves, and tender flower stalks (before they bloom) may be cooked as greens.
The leaves of many arrowhead species typically have arrowhead-shaped leaves. The genus name, Sagittaria, refers to these sagittate leaves and shares its Latin linguistic root with the constellation Sagittarius, the archer.
Some Sagittaria species are commercially important as aquarium plants.
Duck potatoes provide important food for wildlife. Ducks and geese feast on the seeds and/or the submerged corms.
Butterflies, bees, wasps, beetles, flies, and other insects cross-pollinate the flowers as they take nectar and pollen.
Other insects, such as some types of leaf beetles and weevils, aphids, grasshoppers, katydids, and certain larval caddisflies and moths, eat the leaves, stems, and/or rootstocks.
Some mammals, such as muskrat, also eat the plants.
Some aquatic turtles, including snapping turtle, painted turtles, river cooter, and red-eared sliders may eat parts of arrowhead plants.
Plants that grow rooted around the margins of ponds, lakes, ditches, and other sluggish bodies of water play an important role in filtering the water that passes through the soil from higher ground, removing and utilizing nutrients, including artificial fertilizers that might otherwise feed suspended algae that would turn the water green. They also stabilize banks and provide habitat for frogs and lots of other pond-dwelling animals.