The littoral zone refers to the part of a waterbody closest to the shore where light reaches all the way to the bottom. (Courtesy of the Minnesota Dept. of Natural Resources).
Aquatic macrophytes grow in water or in wet areas. Some are rooted in the sediments, while others float on the water's surface and are not rooted to any substrate. Florida has native and non-native (exotic) aquatic macrophytes. Aquatic macrophytes are aquatic plants large enough to be visible to the naked eye. The term is used to distinguish between aquatic plants and algae. The term "aquatic plants" usually refers to aquatic macrophytes, but it can refer to both. (Note: Large visible algae such as Nitella spp. and Chara spp. are included in the category of aquatic macrophytes.)
Aquatic macrophytes are grouped into three general categories:
- submersed aquatic plants
- emersed aquatic plants
- floating and floating-leaved aquatic plants.
Native plants provide food, habitat and shelter for native animals like this Florida softshell turtle.
Submersed plants are macrophytes that grow primarily below the water’s surface. Some species are rooted to bottom sediments and others are free-floating. They come in all shapes and sizes and occur in virtually all Florida waterbodies. Environmental factors such as light, water clarity, temperature, pH, nutrient availability and sediment stability affect where submersed plants will grow.
Tape grass (Vallisneria americana) and hydrilla (Hydrilla verticillata) are rooted in the sediments. Coontail (Ceratophyllum demersum) and bladderwort (Utricularia spp.) are free-floating. Some submersed species (tape grass) produce flowers and are pollinated underwater or at the water’s surface. Sago pondweed (Potamogeton pectinatus) has branches and leaves that spread across the water just below the surface. Fanwort (Cabomba caroliniana) produces flowers that float on the surface. Water milfoils (Myriophyllum spp.) have flower stalks that emerge up to six inches above the water. Some submersed plants have several of these attributes: coontail (Ceratophyllum demersum) is a submersed, free-floating plant that produces tiny flowers pollinated underwater.
Professional management of aquatic plants in Florida is extensive because both native and non-native submersed plants can reach nuisance levels. An abundance of submersed aquatic plants can adversely affect recreational boating, swimming, and fishing; fish and bird populations; commercial navigation; and flood control.
Roles of Submersed Plants in Waterbodies
The importance of submersed vegetation and the amount necessary to achieve specific management goals are subjects of ongoing research and debate. Submersed aquatic plants perform several important functions:
- provide habitat for fish and wildlife
- affect nutrient cycles
- increase water clarity
- stabilize shorelines and sediments
- increase or decrease dissolved oxygen concentrations, depending on abundance and the availability of light
- contribute to muck accumulation
See photos and profiles of submersed plants in Florida.
Emersed plants are rooted in shallow water with much of the vegetative growth above the water.
Emersed plants are rooted in water-saturated soils or submersed soils near the water’s edge. The leaves and stems grow above the water. During low-water conditions, emersed plants can grow in exposed, damp, sediments. Cattail (Typha spp.), maidencane (Panicum hemitomon), and bulrush (Scirpus spp.) are examples of emersed plants. They can grow from the water’s edge to a depth of 1 to 3 meters (3 to 10 feet).
Some emersed plants are large-leaved, with big spikes of flowers: the arrowheads (Sagittaria spp.) and fire flag (Thalia geniculata). Some are small plants, growing inches above the water (Bacopa spp.). Some are viney, rooted in the mud but crawling across the water: water spinach (Ipomoea aquatica). Some are tall and leafy: the native lake hygrophila (Hygrophila costata). Some can fill a large prairie: bur-marigold (Bidens laevis).
Aquatic grasses, sedges, and rushes are also in the emersed-plant category. Among Florida's native giant grasses are sugarcane plume grass (Saccharum giganteum) and giant foxtail (Setaria magna). Shorter grasses, such as maidencane (Panicum hemitomon) and knotweed (Polygonum spp.), grow in shallow marshes and lake margins and are extremely valuable to Florida's fisheries. Sedges include the dominant plant in the Everglades, sawgrass (Cladium jamaicense), and star-rush (Dichromena spp.). Bulrushes include Scirpus spp. and the true rushes of Florida: soft rush (Juncus effusus).
Unfortunately, Florida has many non-native invasive grasses, sedges, and rushes: torpedograss (Panicum repens), paragrass (Urochloa mutica), napier grass (Pennisetum purpureum), and West Indian marsh grass (Hymenachne amplexicaulis).
Emersed plants occur in all Florida waterbodies within a zone from a few feet to hundreds of feet. The zone changes most often in response to changing water levels. When periods of low water are followed by a rapid rise in water level, large sections of emersed plants may be uprooted. Sustained high water can also reduce emersed-plant abundance. In periods of low water, debris from dying emersed plants is a significant factor. Accumulated plant debris can eventually result in the lake becoming shallower, or even transitioning into a swamp or marsh.
Roles of Emersed Plants in Waterbodies
Emersed plants perform many functions in waterbodies:
- provide habitat for wildlife
- provide food (seeds and leaves) for waterfowl
- reduce shoreline erosion
- shed leaves and other plant debris, adding to the sediments. Uprooted plants can form floating islands or tussocks that can pose significant navigational hazards and block access to portions of the waterbody. Tussocks also provide bird and wildlife habitat.
See photos and profiles of emersed plants in Florida.
Free Floating and Floating Leaved Plants
Floating-leaved plants are typically rooted in the bottom sediments with leaves floating on the water surface, like these native fragrant water lilies.
The “floating” category of aquatic macrophytes includes free-floating and floating-leaved plants. Free-floating plants are not anchored in the sediment; they obtain their nutrients from the water. Florida’s native free-floating plants include the world's smallest flowering plant (a duckweed called water meal, Wolffia columbiana); and two larger duckweeds,small duckweed (Lemna valdiviana) and giant duckweed (Spirodela polyrhiza). Other native free-floating plants are bladderwort (Utricularia spp.) and coontail (Ceratophyllum demersum).
The free-floating plant, water hyacinth (Eichhornia crassipes), is a non-native invasive plant in Florida and has been called "the worst aquatic weed in the world" by experts. In many Florida waters, it requires constant management, known as maintenance control to maintain low levels and keep waterways passable. Water hyacinth has invaded the waters of many countries from its native Brazil; and is profiled here. Salvinia (Salvinia spp.) and water lettuce (Pistia stratiotes) are also non-native invasives that form dense mats covering the water surface.
Floating-leaved plants typically are rooted in the sediments and have leaves that float on the water surface. Water lilies (Nymphaea spp.), spatterdock (Nuphar lutea subsp. advena), American lotus (Nelumbo lutea), and water shield (Brasenia schreberi) are examples of floating-leaved plants. They generally grow along the shoreline, lakeward of the emersed plants.
Floating and floating-leaved plants occur in many Florida waterbodies. Rooted floating-leaved plants can grow completely across shallow waterbodies. The roots of floating-leaved plants provide a stable surface for successful fish spawning.
Roles of Floating Plants in Florida Waterbodies
Floating plants and floating-leaved plants perform many functions in waterbodies:
- provide food and habitat for fish and wildlife
- reduce shoreline erosion
- Floating-leaved plant debris contributes to sediment, making a waterbody shallower.
- If periods of low water are followed by a rapid rise in water level, the roots of dead floating-leaved plants (called rhizomes) can float to the surface, block access, and hinder navigation. In many cases, masses of floating rhizomes (especially from the native plant spatterdock, Nuphar advena) can form floating islands that grow large enough to support trees. Water hyacinth and water lettuce may completely cover the surface of a waterbody and cause major problems for fish and wildlife habitat, recreation, navigation, and flood control.
- Floating and floating-leaved plants are not generally considered a human health concern, but they provide breeding habitat for mosquitoes.
- The stems of floating-leaved plants (spatterdock) often contain burrowing insects called bonnet worms that some anglers use for bait.
See photos and profiles of floating and floating-leaved plants in Florida.