Lakes are productive freshwater ecosystems that, just like most terrestrial biomes on land, contain a wide variety of living organisms. Some of their most important components are photosynthetic and are thus able to generate oxygen and nutrients under adequate sunlight. These include algae, cyanobacteria, phytoplankton, and, of course, plants. Plants form the backbone of self-sustaining lake systems and are extremely important for ecological balance.
In the lakes of North America, great and small, freshwater plants are found at several depth levels or zones. They are usually most abundant along sunlit bottoms, where their stems grow toward the water’s surface, and along the margins and edges, where the depth level is variable. Their position relative to the lake is associated with the roles they play in keeping it healthy and free of toxins.
For example, those along the shoreline can help prevent erosion whereas those on the lake floor may be important oxygenators. Freshwater plants are especially beneficial when they are present in controlled densities and when their vectors for spread are minimized. In the Great Lakes region, invasive plants are unfortunately becoming more common. To increase your awareness whenever you visit one of North America’s lakes, both native and invasive species are included in this list.
1) Coontail (Ceratophyllum demersum)
Made remarkably popular by the aquarium industry, this common aquatic plant is known for being a rapid grower in high-nutrient bodies of freshwater. Given enough sunlight, water flow, and moderate temperatures ranging from 15 – 30˚C (59 – 86˚F), its bright green stems can grow as tall as 10 feet (3 meters). A single healthy plant is capable of producing numerous side shoots, giving it a bush-like appearance.
Usually found in the submergent marsh zone or in emergent zones that flood frequently, coontail or hornwort is distinguished by its whorls of threadlike and feathery leaflets. It is chiefly spread via fragmentation, which occurs when segments of its stem break off and eventually root into fertile substrates.
Coontail is also capable of excreting biochemicals that may inhibit the growth of native plants. These chemicals, coupled with the plant’s capacity for vegetative spread, make it remarkably competitive. If you grow this species in your pond or aquarium, it would be prudent to take extra measures to prevent its entry into public waterways.
2) Common waterweed (Elodea canadensis)
Also known as the Canadian pondweed, this submerged waterweed is a low-maintenance perennial. It thrives best in cool temperatures and under full sun exposure. Segments of mature plants can survive as free-floating specimens, though they may eventually take root once they come into contact with the appropriate substrates. When found in optimal densities, they aid in keeping the water clear and free of excess nutrients.
The common waterweed is able to stay green throughout winter. Its shoots can persist even under a layer of ice! Come summer, fertile shoots may produce tiny flowers with up to 3 white petals each. Arguably the skinniest of aquatic flowers, they are borne on tubes that grow up to 30 cm (12 inches) long yet remain just 1 mm (0.04 inches) in width. The unique blooms are usually found on the surface of calm waters, where they may eventually develop into capsule-like fruits.
3) Eurasian watermilfoil (Myriophyllum spicatum)
One of the most infamously invasive aquatic plants found throughout North America, M. spicatum is a perennial species with a chiefly submerged habit. It has choked many waterways and has outcompeted dozens of native aquatic plants in some of the most productive lake systems. Its mature colonies are often referred to as infestations. Their dense canopies can block out sunlight, oxygen, and water flow, transforming lakes into stagnant bodies of water.
Introduced into the continent via the aquarium trade, ballast water, and other forms of aquatic transport, the Eurasian watermilfoil can produce stems that grow to 20 feet (6 meters) long. Despite its preference for shallow water (1 – 10 feet or 0.3 – 3 m deep), it can grow further inward in lakes as it can tolerate a depth of up to 33 feet (10 meters). This species is set apart by its reddish stems and feather-like leaves, which are arranged in whorls of four leaves each.
4) Curly-leaf pondweed (Potamogeton crispus)
The curly-leaf pondweed is just one of many Potamogeton species found throughout North America. In its native range, which extends throughout most of Asia and Europe, it is often found growing in standing freshwater bodies. The best growth rates have been observed in calcareous and slow-moving pools, where its submerged stems can grow to about a meter (3 feet) long. Its ability to survive in relatively poor conditions has allowed it to be competitive in American waters.
This perennial herb is characterized by flattened shoots, from which its wavy-edged leaves arise in an alternate orientation. The leaves may differ in color according to season. Young ones tend to be bright green before they take on an olive green to brownish hue. Blooms, which appear as short and spiky inflorescences, jut through the water’s surface. Although this pondweed does flower, its most effective means of spread is via rhizomatous growth.
5) Pickerelweed (Pontederia cordata)
An emergent aquatic plant, pickerelweed is often found along the margins of lakes, ponds, rivers, and streams throughout its native range. It is capable of persisting in flooded shorelines due to adaptations in its stems (equipped with lacunae), which shuttle oxygen into its root system. In its microhabitat, where water levels naturally fluctuate throughout the year, it grows best in fertile soil and under full sun.
Pickerelweed draws many pollinators to lake shorelines because of its alluringly colored inflorescences. Appearing in late summer, the purple flowers arise from gracefully upright stalks, beckoning bees and butterflies. Once seeds are produced, the floral stalks bend in the opposite direction to submerge the ripe fruits. This species can also reproduce via rhizomes, but it is not generally known for being troublesome.
6) Arrowhead (Sagittaria latifolia)
The arrowhead is a lovely marginal herb, earning its name from the three-tipped shape of its large leaves. Its importance to several Native American communities is evident in that it has many other names, such as Indian potato, katniss, duck-potato, and wapato. This plant’s tubers are highly edible and can be eaten either raw or cooked. In terms of taste, they have been likened to chestnuts and potatoes.
The emergent shoots of arrowhead tend to form colonies along the curved shorelines of lakes, rivers, and ponds. They arise from relatively strong roots, which can keep the plant anchored when weather conditions are harsh enough to create waves. They can also tolerate high phosphate levels and may even thrive under a high nutrient load. The size of a mature plant is highly variable, with the oldest specimens of healthy populations reaching several meters tall!
7) Greater bladderwort (Utricularia vulgaris)
As its common name suggests, the shoots of U. vulgaris are equipped with tiny, gas-filled sacs which function as air bladders. These maintain the free-floating nature of this permanently rootless species. The specialized leaves, which are mostly submerged, occur alternately and resemble the appearance of fine twigs along a branch. Forked and threadlike, their filaments are attached to a central stalk.
One of the most interesting characteristics of this freshwater plant is its capacity to trap tiny organisms. Because it is able to metabolize these organisms, it is considered a carnivorous species! The mechanism by which it traps small animals is a specialized door on its trap bladders. Dotted with sensitive hairs, these doors can quickly open and close to suck in and ensnare unsuspecting insects, zooplankton, and more!
8) Eelgrass (Vallisneria americana)
Also referred to as tape grass or wild celery, eelgrass is an aquatic plant that can grow along the shorelines of waterbodies with a mild to considerable current. Its deep roots keep it anchored as its flattened leaves move in the direction of water flow. The leaves help filter out particles and nutrients from moving water, while the roots aid in shoreline stabilization.
Many animals are able to benefit from the nutritious parts of this plant. In particular, the West Indian manatee (Trichechus manatus) can live on a diet of eelgrass and other similar aquatic herbs. They can feed on a large amount of eelgrass each day, digging up the plant’s roots and bringing up loosened substrates in the process.
Fortunately, eelgrass beds can quickly become replenished due to their capacity to spread via underground runners. These beds are known for being able to tolerate saline conditions and for serving as a refuge to many other small animals.
9) Sago pondweed (Stuckenia pectinata)
With leaves and tubers that are favored by a wide range of waterbirds, sago pondweed is ecologically beneficial in controlled numbers. Populations aren’t necessarily troublesome in clean waters, but they can become a nuisance in polluted systems. A high nutrient load is tolerated by this species, giving it a competitive edge. Its rapid spread is also enabled by fragmentation and rhizome growth.
Sago pondweed is distinguished by its thin and linear leaves, which can measure up to 6 inches (15 cm) long but maintain a width of just 0.5 inches (1.3 cm) wide. The submerged leaves afford protection to many macroinvertebrates, which also benefit from the particles that may grow on the plant’s surfaces. In turn, these small animals attract larger vertebrates, facilitating a complex food web.
In areas where great masses of sago pondweed choke freshwater systems, their colonies may need to be controlled. Management is usually done through the combined use of herbicides, biological treatments, and physical removal.
10) Common spatterdock (Nuphar advena)
The common spatterdock is also known as the yellow pond lily or cow lily due to its similarity to the more popularly grown waterlilies. It is slightly different from typical waterlilies as its leaves often occur on emergent petioles, meaning they are held a few inches above the water’s surface. Although this species is not classified as a floating plant, some leaves may remain on the surface. A closely related spatterdock (also found in North America), N. variegata, tends to have more floating leaves.
Spatterdock colonies are found in protected areas with clear water. Their leaves have smooth margins and measure about 6 – 12 inches (15 – 30 cm) long. A cleft divides each leaf into two lobes, where veins faintly mark the smooth surface and extend toward the edge of the blade. Solitary blooms occur on their own emergent floral stalks. They are often seen peeking through the gaps for some sun in between the larger leaves.
11) Rushes (Juncus spp.)
Rushes are closely related to grasses and sedges, with which they are often confused. One of their key differences lies in floral morphology, so it may be quite difficult to distinguish these families from one another outside of the bloom period. Pay close attention to their stems, which have a rounded cross-section. These differ from the triangular stems of sedges and the knobby, hollow stems of grasses. Keep in mind that ‘sedges have edges, rushes are round, grasses have knees that bend to the ground’.
Commonly found in wet areas, many rushes grow as marginal aquatic plants. Their roots can persist in substrates that are submerged under a few inches of water. The shoots grow in an upright manner and are usually emergent. They create a protected environment and increased surface area on which many hatchlings and juvenile fish are able to feed.
Some of the most common rushes in the lake systems of North America include soft rush (J. effusus), toad rush (J. bufonius), Baltic rush (J. balticus), and path rush (J. tenuis). Due to their ease of care and textural features, they make for ideal plants around outdoor water features.
12) Water stargrass (Heteranthera dubia)
Although water stargrass is chiefly found as a submerged freshwater plant, mature specimens may dot river and lake margins as well as exposed shorelines. This perennial species has variable features which differ based on water conditions and genetic variation. Even the force with which water bathes the plant influences the shape and size of its leaves. Stem morphology is likewise affected by the plant’s position relative to water.
Generally, H. dubia is distinguished by its yellow, star-like blooms which appear from July to October. Each of these persists for just one day, opening up their linear petals in the morning and wilting at dusk. The leaves of submerged water stargrass usually resemble ribbons and have parallel venation. They can grow up to 6 inches (15 cm) long in optimal conditions.
13) Common duckweed (Lemna minor)
Considered one of the smallest flowering plants on Earth, the common duckweed is a freshwater species that creates floating colonies. To accurately identify this species and tell it apart from other types of duckweed, you may need a magnifying glass! With leaves that seldom grow to more than 8 mm (0.3 inches) long, this plant remains on the water’s surface not just because of its diminutive size but also due to the presence of air pockets.
Common duckweed can be a bane or benefit to the lake systems they inhabit. While well-balanced conditions and ample shading help control populations, an influx of nutrients can cause total colonization of the water’s surface. When present in healthy densities, duckweed effectively reduces algal growth and prevents toxic nutrient buildup. As a result, it has been proposed as a biological agent for wastewater recovery and wetland remediation.
14) Cattails (Typha spp.)
One of the first images that come to mind when one thinks of plants around a pond, the humble cattail comes in about 30 flowering species. Also known as reed or bulrush, these wetland staples tend to be dominant wherever they are found. They form considerably-sized populations along the margins and edges of ponds, lakes, and streams. In some cases, their rapid growth and spread can be problematic as they compete with other native plants.
In North America, some of the most common cattail species include the broadleaf cattail (T. latifolia), narrowleaf cattail (T. angustifolia), and southern cattail (T. domingensis). Interestingly, a hybrid between the first two aforementioned species is known for being a rapid spreader and has shown potential for invasiveness. Formally referred to as Typha x glauca, this hybrid taxon is especially problematic in the Midwest.
15) Water lilies (Nymphaea spp.)
The most popular of all ornamental freshwater plants due to their attractive floating leaves and bright blooms, water lilies come in hundreds of eye-catching cultivars and wild forms. The species that are most common in the lake systems of North America are N. odorata and N. tuberosa. The white-flowering lilies produce sweetly-scented blooms and are beneficial to ornamental ponds.
Perennials that chiefly spread via rhizomatous growth, water lilies attract many pollinators (especially bees and beetles) to wetlands and garden ponds. Their large fronds provide protection to countless small animals while aiding in temperature regulation and the reduction of algal growth. Many aquatic and terrestrial herbivores that feed in the shallows benefit from their nutritious components. These plants grow best in moderate temperatures, shallow water, and full sun exposure.
16) Purple loosestrife (Lythrum salicaria)
Purple loosestrife is a flowering perennial that favors moist conditions along the borders of lakes. It can also grow as an emergent plant because its shoots can tolerate being submerged in a few feet of water. Mature plants can grow as tall as 9 feet (2.7 meters) in optimal conditions. They may look quite stunning in colonies, but don’t be fooled! This species is known for being invasive – just a single root clump can generate multiple fertile stems.
A cross-section cut through the stems of purple loosestrife reveals that they are square in shape. Leaves numbering in threes arise as whorls along the length of the stem. The densely packed blooms, which come in pink to purple hues, appear along the axils of the terminal leaf whorls. They attract bees, butterflies, and beetles, some of which may heavily feed on the leaves and buds. These insects have thus been used as a biological means of minimizing this plant’s spread.
17) Common reed (Phragmites australis)
A type of grass that is arguably one of the tallest and fastest-spreading of its kind, the common reed is an aggressive plant. In warm regions of North America, the stems of this invasive species may easily grow to about 13 feet (4 meters) tall or more. Moreover, they arise from horizontally spreading runners which set down new roots every few feet. Mature plants can generate shoots as far as 16 feet (5 meters) away from the primary root clump within just a single year.
The common reed is capable of thriving as an emergent plant in up to 3 feet (1 meter) of standing water. Its leaves can create floating mats that eventually overgrow wetlands. Because of its tolerance for moderate salinity levels, its colonies (better known as reed beds) may extend toward estuarine zones. In the absence of livestock to feed on their growing shoots, common reeds are more likely to exhibit uncontrollable growth.
18) True sedges (Carex spp.)
Sedges are grass-like perennials. The genus to which they belong is one of the vastest and most widely distributed among all flowering taxa. With anywhere from 1,000 – 2,000 species, many of which are under taxonomic debate, they are quite common in North America. In the US, some of the most common sedges in lake systems include the water sedge (C. aquatilis), Bebb’s sedge (C. bebbii), lake sedge (C. lacustris), and tussock sedge (C. stricta).
Typically characterized by triangular and non-hollow stems, sedges produce linear leaves that partly function as sheaths. The sheaths are tightly fused around the stems, all three sides of which are capable of producing leaves. Sedge flowers arise as small and spiky clusters, which may resemble the appearance of fireworks at the peak of explosion!
