Nelumbo lutea (Willd.) Pers.: American lotus, yellow lotus, water chinquapin. Nelumbonaceae (lotus family).
Native perennial. Dense colonies can be found in still water to 6 ft (1.8 m) deep. Leaf and flower stalks arise directly from spongy rhizomes rooted in the substrate. Milky sap is found throughout the emergent parts of the plant and contains alkaloids similar to the drug-generating compounds common in other species of lotus. The circular leaves float flat on the water when young and later emerge to 3.3 ft (1 m), held up by stout leaf stalks attached to the middle of the underside of the blade. The large, waxy, plate-like leaves, 12 - 28 in (30 - 70 cm) wide, have no notch or indentation; the undersides have prominent ribs. Leaves held above the water surface are shallowly depressed at the center. The extremely showy yellow flowers emerge from a large egg-shaped bud. The flower is many-petaled, fragrant, 4 - 10 in (10 - 25 cm) wide, and carried up to 3.3 ft (1 m) above the water. A large fleshy funnel-shaped receptacle holds the nutlike fruits within pits on its surface; it hardens and turns brown as it dries, and the oval fruits (nuts) become loose within it. This is a very competitive species, able to reduce wildlife habitat diversity and to hinder water flow and access.
Limnobium spongia (Bosc.) Steud.: Frog's bit. Hydrocharitaceae (frog's bit family).
Native perennial. The plant is made up of a rosette of leaves that usually floats freely; older plants can root in mud to form dense mats. Roots lined with hairs emerge at the base of the rosette; daughter plants are produced on slender stolons. In unrooted pre-flowering plants, the rosette of young heart-shaped leaves lies flat on the water surface. Leaf blades are 0.8 - 2 in (2 - 5 cm) long, with slender, flexible leaf stalks. A distinct inflated area of purplish spongy cells on the underside of the leaf blade adds buoyancy; networks of cross veins can be seen between the main veins. At maturity and flowering, leaf stalks are spongy and thicker (but not bulbous), up to 6 in (15 cm) long, with two ridges down their length. The rounded oval leaves are held above the water to 1 ft (30 cm). While these older leaves are thicker and less heart-shaped, cross veination remains. The white flowers are clusters of thread-like petals, held on short stalks at the base of the plant; as the spherical, green-striped berries mature these stalks curve downwards.
Salvinia molesta Mitchell: Giant salvinia, kariba-weed, water spangles. Salviniaceae (water fern family).
Exotic perennial. This plant is a small, oval-leaved fern that floats on the surface of the water; in spite of its small size it can produce extreme water-use problems by reproducing rapidly and creating dense mats to 3 ft (90 cm) thick. Individual, uncrowded, plants consist of two floating leaves and one underwater leaf that looks like a feathery root. The paired floating leaves are small, 0.5 - 1 in (1.25 - 2.5 cm), oval, with a shallow notch at the base and a distinct incised midvein along which the leaf may fold inwards as plants become more crowded. The dense hairs that cover the upper surface of the leaves split into several divisions at their ends and then fuse back together, forming a small sphere of filaments at the tip of each hair; these can be usually be seen without magnification. As colonies expand and become denser, plants produce leaves crowded alternately along a short hidden stem. Small, round, brown, seed-like sporocarps may be produced from underwater parts. Salvinia is a major long-term weed problem in many parts of the world, now being faced in the U.S.
Lemna minor L.: Small duckweed, duckmeat. Lemnaceae (duckweed family).
Native. Individual plants consist of one to several very small (0.1 in; 2.5 cm) smooth oval leaves that lie almost flat on the water surface and float freely. The leaf has a slightly raised midvein on its surface. Roots and flower parts are present but difficult to see. Plant colonies can cover broad areas of calm water in ponds and lakes, and may mass up against shorelines. They can create a nuisance to water flow and aesthetics.
Spatterdock, Cow Lily
Nuphar advena (Ait.) Ait.f.: Spatterdock, yellow water lily, cow lily. Nymphaeaceae (water-lily family).
Native perennial. The whole plant is stout and robust, a denizen of slow-moving shallow water and areas of wet muck. Thick rhizomes grow in the substrate, increasing to 4 in (10 cm) in diameter; they are often rough and marked with crescent-shaped leaf scars. Leaves can be submersed, floating flat on the water, or held above the surface. The large leaf blades have an elongated heart-shape, but are less than twice as long as wide, 6 - 14 in (15 - 35 cm) long and 5 - 10 in (12.5 - 25 cm) wide. Leaves have long rounded lobes at the base; the margins are smooth to wavy. The wide midrib is flat to concave; side veins, parallel to each other, emerge all along its length. The cylindrical spongy leaf stalk grows to 3 ft (90 cm) long; it attaches to the leaf blade at the deep basal indentation or notch. Spherical-looking yellow flowers are borne above water on stout stems up to 6 ft (1.8 m) long. The cupped petals surround a flat yellow disk that becomes the top of a ridged, green or yellow, pot-shaped fruit. Leaves, flowers, and fruit differ from the related Nymphaea waterlilies.
Exotic perennial. Forms extensive, dense, floating mats of robust plants interconnected by spongy stolons. Plants can reach up to 3.3 ft (1 m) in height but are usually found at 9 - 12 in (22.5 - 30 cm) tall. The numerous roots with their large stout root hairs are easily seen by pulling a plant out of the water; these roots do not anchor in the substrate. The leaf blade is short, leathery, broadly oval to circular, and parallel-veined; it is held upright on a spongy leaf stem with a swollen to bulbous midsection that gives the plant buoyancy. Showy clusters of orchid-like lavender flowers are held above the water on stout stalks; the flower has a yellow dot in the upper petal. Stem runners or stolons emerge from plants at the water surface and generate daughter plants that multiply in turn. Rapid vegetative reproduction and its impenetrably dense biomass make this species a major noxious weed. It destroys native aquatic habitat and interferes with all water uses. Although plants may be used as livestock forage or compost, and have provided fiber material in the tropics, water hyacinth has nuisance status everywhere it has been introduced. When comparing this plant with Limnobium spongia, note the showy purple flower, swollen leaf stalks, and absence of spongy cells on the underside of the leaf in water hyacinth.
Pistia stratiotes L.: Water lettuce, water bonnets. Araceae (arum family).
Perennial, possibly exotic. This floating, unattached plant consists of a large open rosette, 18 in (45 cm) or more in width, made up of coarse leaves and numerous feathery roots; it produces horizontal stolons that give rise to daughter plants. The light- to yellow-green leaves are stalkless, and wider at the blunt to slightly rounded top than at the base. Leaves are covered with short, dense, velvety hairs; parallel veins run down the leaf in shallow grooves, giving the leaf a striped or rippled look. Inconspicuous flowers are borne centrally in a leaf-like structure. This plant can increase rapidly in numbers and biomass, becoming weedy over large areas; it causes major problems with water flow and water use in lakes, rivers, and canals.
Wolffia columbiana Karst: Watermeal. Lemnaceae (duckweed family).
Native perennial. This light-green floating, rootless, plant is smaller than the duckweeds (Lemna spp.); it can cover areas of still water and may be mistaken for algae. The leaves are broadly oval, with a flattened, unridged, surface. They are 0.05 in (1.5 mm) wide/long; 25 - 50 leaves can fit on a drop of water. Plants feel gritty or mealy when rubbed between the fingers. The leaves are uniformly green, unlike other Wolffia species, whose leaves may appear to have lighter and darker areas or scattered white dots. Plants multiply by the growth of new leaves 'budding' from ends of existing leaves. Often found among duckweeds; sometimes in pure stands.
Brasenia schreberi Gmel.: Water shield, dollar bonnet. Cabombaceae (water-shield family).
Native perennial. This plant can grow in water up to 6 ft (1.8 m) deep; it produces floating leaves that can overlap and may completely cover surface areas. Long leaf stalks emerge alternately from a short underwater stem or creeping rhizome rooted in the substrate. Leaf blades are smooth, very broadly oval, up to 4.75 in (12 cm) long; they do not have any notch or indentation. The leaf stalk attaches to the center of underside of the blade. The underwater parts of the plant, including the underside of the leaf and the leaf stalk, are reddish-purple and slimy, covered with a thick mucilaginous coating. Conspicuous flowers, each a cluster of reddish-purple flower parts 0.75 in (2 cm) long, are held singly above the water on stout stalks.
Nymphaea odorata Ait.: White or fragrant waterlily, pond-lily. Nymphaeaceae (water-lily family).
Native perennial. Cylindrical rhizomes in the substrate produce leaf and flower stalks in calm to slowly flowing water. The floating leaves are round to oval in shape, 6 - 12 in (15 - 30 cm) wide, with a triangular notch cut out almost to the center. The resulting basal lobes look more right-angled than rounded. The leaf stalk joins the blade at the apex of the notch and multiple veins fan out from this point. The underside of the leaf is usually reddish-purple. The showy, very fragrant, multi-petaled flowers, 3 - 6 in (7.5 - 15 cm) across, float on the surface; they close at night and in low light. This waterlily differs from spatterdock in the shape of the leaf, particularly the lobes, and in veination pattern, along with flower appearance. It can cover large surface areas but stands are rarely dense enough to cause problems.