Aquatic plants are most easily identified by how and where they grow in a wetland environment. While most water plants aid in transforming the waste of animals and decaying plant matter into fertilizer through a process referred to as "the nitrogen cycle"; the varied classifications of water-loving plants have different functions in the pond as well.
Plants left entirely uncontained in a pond fall into the category of free-floating water plants. The exposed roots of these plants dangle into the water while the foliage extends above the water up to 6 inches. Free-floating plants reproduce by sending off "shoots" of baby plants, making most of them prolific propagators in the right conditions.
The ability of these plants to reproduce and spread inhibits algae growth and aids pond clarity by shading the sunlight. Water hyacinth, water lettuce and duck weed fall into this category of free-floating plants.
Floating with Planted Roots
Water lilies, water lotus and other lily-like aquatics are plants anchored into the soil completely submerged in the water with foliage and blossoms extending up to the surface. Like free-floating plants, these plants aid in water clarity by shading the pond. The abundant leaves grow from a tuber called a rhizome that is planted just under the surface of the soil. Roots extend into the soil from the rhizome while the rhizome itself grows longer over time, forming more "eyes" from which leaves and flowers sprout.
Emergent aquatics are also considered "marginals" due to their preference to be placed in just enough water to saturate their roots and no deeper than 6 inches under the surface. The foliage of these plants is extremely diverse, from the enormous heart-shaped leaves of the taro to the delicate ground-cover of Siberian pink cups. Generally, emergent plants line the outer edges of a pond to provide beauty and habitat for non-aquatic wildlife.
Plants that grow under the surface of the water are considered submerged aquatics. Many plants in this category transpire oxygen through their leaves and provide a dense covering for fish to spawn in. Many submerged plants have a "feathery" appearance like Parrot's Feather, Anacharis and Watermilfoil. These plants are typically anchored to the bottom of the pond but do not draw nutrients from the soil through their stems, therefore, submerged plants may indeed grow freely underwater.
At one time in their existence, most ponds encounter an excessive algae problem. Whether the long strands of filamentous algae strangle aquatic life or plankton algae turns the water so green aquatic life cannot survive, algae is a nuisance to most pond owners. However, the slippery, green/brown coating on hard surfaces in the water is also algae. This "beneficial algae" emits oxygen into the water during the day, provides a tasty treat for fish to eat and competes with harmful algae for nutrients.