Nuisance Aquatic Plant ID
Common Nuisance Water Plants in Missouri Ponds and Lakes
Filamentous algae--also called "moss" or "pond scum"--forms green, cottony masses that are free-floating or attached to rocks, debris or other plants. These masses consist of fine, green filaments that have no leaves, roots or stems. They often form dense, floating mats that make fishing or swimming impossible and can easily clog water intake screens.
Chara (Chara spp.)
Chara is easily identified by its crisp, gritty texture, musky odor and gray-green, needlelike structures that resemble leaves. These curious underwater plants are actually large algae, growing in a form that makes them look like more advanced, flowering plants. The grittiness comes from a thick coating of lime, which the plants extract from the hard, alkaline water in which they are commonly found.
Chara is undesirable in ponds and lakes because it carpets the bottom and crowds out other species.
Coontail (Ceratophyllum demersum)
Coontail is rooted to the bottom but sometimes forms large, tangled masses which float freely in the water. The stems can reach 6 feet or more, with much branching. The leaves are grouped in whorls around the stems, and each leaf is needlelike, forked once or twice and covered with small thorny projections. Coontail is usually completely underwater and feels stiff and brittle.
The common name of this plant comes from the crowded upper leaves, which make the stem tip appear bushy like the tail of a raccoon.
Several other plants with narrow leaves resemble coontail. Make sure that the leaves are needlelike, have thorny projections and are forked only once or twice.
Water Milfoil (Myriophyllum spp.)
Below the waterline, the leaves of the water milfoils are divided into threadlike segments and look almost like feathers. Above the water, they are blade-like with serrated edges. The rooted stems may be up to 6 feet long.
Missouri has two native species of water milfoil and one or two that are introduced. The introduced species, especially Eurasian milfoil, can cause serious problems in Missouri ponds and lakes.
Naiads (Najas spp.)
Naiads are slender, narrow-leaved plants that grow completely underwater and are rooted to the bottom. The leaves have finely toothed edges and occur in pairs or whorls. Each leaf base forms a sheath around the stem. A key characteristic is the presence of tiny, greenish flowers at the bases of the leaves.
These plants may be hard to distinguish from some of the narrow-leaved pondweeds and other similar plants. Note that naiads never have broad, floating leaves or conspicuous flowers or seed heads.
Missouri has two or three species of naiad. The most common nuisance species is southern naiad, shown in the accompanying photo.
Pondweeds (Potamogeton spp.)
All pondweeds have underwater leaves scattered on long (up to 6 feet), flexible stems that are rooted to the bottom. Some have floating leaves, which usually have a different shape than the underwater leaves.
Among the species, the leaves range from large, round and leathery to small, needlelike and delicate. The small, greenish flowers are borne on a spike which extends above the water for wind pollination, then sinks below the surface. Pondweeds can spread by rhizomes (modified underground stems), winter buds, seeds or fragmentation, depending on the species.
Missouri has 10 species of pondweed. Some are not considered problem plants, but it is a good idea to control the spread of any pondweed in a pond or lake. Several species tend to grow rampantly and invade deep water. The three species shown here are the pondweeds most often reported as problems in Missouri ponds and lakes.
- Variable-leaf pondweed (P. diversifolius)
- American pondweed (P. nodosus)
- Leafy pondweed (P. foliosus)
Duckweeds and Watermeal
Each duckweed plant is a green, floating disc less than 1/4 inch across; several plants fit easily on a fingertip. They occur singly or connected in groups. Some duckweeds have hair-like roots that dangle into the water. Watermeal is the smallest duckweed; each plant is about the size of a pinhead. Missouri has seven species of duckweeds and two of watermeal.
Duckweeds spread quickly, especially when nutrients such as nitrogen and phosphorus are plentiful. A single Lemna minor plant can reproduce itself about every three days; at this rate, a square inch of this species could cover an acre in 55 days.
Dense duckweed growth will block out sunlight, which all plants need to produce oxygen. This can reduce dissolved oxygen levels and destroy the pond's natural balance. Duckweed mats often develop on old, nutrient-rich ponds, and those contaminate with feedlot runoff or sewage.
Water Shield (Brasenia schreberi)
The oval, floating leaves of water shield may reach 4 to 5 inches in length and resemble small water lily leaves. Unlike the water lily, however, water shield does not have a large, showy flower and its leaves are without a split or cleft.
The most outstanding feature of the water shield is the thick, jellylike covering on the young stems, buds and lower leaf surfaces. Underwater parts have a reddish or purplish tinge.
Water shield is one of the worst plant pests in ponds and lakes. It spreads rapidly by rhizome growth, and can cover the surface of a pond in a few years. It is difficult to control.
Water Lily (Nymphaea spp.)
Water lilies are among the most beautiful of all water plants. They have large, round leaves (8 to 16 inches across), each with a single V-shaped notch. The leaves may be floating, elevated above the water surface or submerged, depending on water level fluctuations. Their large, showy flowers are typically white to pink and do not have the central disc found in the yellow flowers of the American lotus. Leaves and flowers are attached to flexible underwater stalks that rise from thick, woody rhizomes (modified underground stems) on the pond or lake bottom.
American Lotus (Nelumbo lutea)
Despite its ornamental qualities, American lotus should not be introduced into most fishing ponds. Lotus spreads rapidly in shallow water and can completely cover a 1-acre pond in three to four years.
The yellow blossoms, some as big as a dinner plate, rise several feet above the water on long stalks. The blue-green leaves are completely round and may be up to 2 feet wide, with the stem attached in the center. Unlike water lily leaves, those of American lotus do not have a cleft. The young leaves float, and the larger, older leaves, like the flowers, stand erect on long stems above the water's surface.
In the center of each flower is a seed-bearing structure resembling a shower head called a receptacle. The receptacle starts out soft and yellow, but as the petals fall and the seeds mature it becomes hard, dried and brown. Although American lotus regularly produces seeds, it spreads mainly through thick rhizomes that grow along the pond bottom.
Cattails (Typha spp.)
The three cattail species in Missouri all have the same trademark appearance: tall plants with narrow, upright leaves emerging from a thick base, and a central stalk bearing a brown, sausage-shaped flower spike. They spread from thick, fleshy rhizomes and from the thousands of fluffy seeds released when the flower spike disintegrates.
Too many cattails are undesirable because they crow out other plants and tend to gradually fill in old shallow ponds where water depths are less than 2 feet. This happens because old cattail growth accumulates around the pond's edge, collecting soil and providing a rooting medium for terrestrial plants. Cattails grow rapidly--in six months, a single plant can cover an area 10 feet in diameter--so they can quickly close up a small pond.
Cattails should be removed from dams and spillways. On dams, they encourage burrowing by muskrats; on spillways, they can impede the discharge of rainwater after a storm.
Water Primrose (Ludwigia peploides)
This shoreline plant is known best for its bright yellow flowers, which appear from May to October. It is common in Missouri, growing in dense mats in the shallow areas of ponds, lakes and streams. The stems are long and trailing, often creeping out from shore over the water's surface. The leaves range in shape from oval to willowlike, and are arranged alternately on the stem.
A distinctive feature of water primrose is its air roots or "breathing" roots. These white, spongy, floating structures are believed to absorb gases from the air.