Aquatic plants are those that live and grow in water bodies. Like their terrestrial counterparts, they play various essential roles in supporting aquatic ecosystems. Aquatic plants are chief sources of oxygen in underwater environments, both freshwater and saltwater bodies alike. They are also a source of food to local fishes and animals; in addition to which they provide shelter and safe nesting spaces to the various underwater inhabitants. The presence of a healthy population of local aquatic plants helps stabilize underwater slopes and anchor soft sediments, along with removing unwanted suspended particles and nutrients. Plants such as marine macro-algae have significant demand in the food and hydrocolloid industries and are extensively cultivated around the world.
Based on the positioning of their roots and leaves, aquatic plants are broadly divided into four main groups- algae, floating plants, submerged plants, and emerged plants.
- Algae: Algae are photosynthetic predominantly aquatic organisms that lack true roots, stems or leaves. They belong to the kingdom Protista and thrive in oceans. In addition to their roles as oxygen suppliers, they serve as the base of the oceanic aquatic food chain, providing nourishment to various aquatic lifeforms ranging from fishes and turtles to whales. These floaters contribute to the human world in being an important source of crude oil, and are in great demand in pharmaceutical and food industries.
- Floating-Leaved Plants: These plants lack any attachment to the floor of the aquatic ecosystem; instead they float on the surface and possess roots which absorb water. The leaves are firm and flat in order to absorb water.
- Submerged Plants: Submerged plants are rooted to the floor and are completely submerged underwater. They have thin, narrow and flaccid leaves, most of which do not break the water surface. Examples are pondweed, coontails and hydrophila.
- Emerged Plants: Like submerged plants, emerged plants are also rooted to the bottom. However, they differ in that most of the vegetaions grows above the surface of water. Their stems are stiff and firm, and they are in need of constant sunlight for optimum growth. Examples include cattails and knotweeds.
While they have a wide range of ecological benefits, many aquatic plants like water hyacinths are invasive species that derange local fauna and are commonly seen as pests.