Water Hyacinth, Hardiness Zone 8-10 (Eichhornia crassipes). Water hyacinth is a free-floating perennial aquatic plant native to tropical and sub-tropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as 1 meter in height. The leaves are 10–20 cm across, and float above the water surface. They have long, spongy and bulbous stalks. A straight stalk supports a single spike of 8-15 conspicuously attractive flowers, mostly lavender to pink in color with six petals. When not in bloom, water hyacinth may be mistaken for frog’s-bit. The Hyacinth can reproduce by the ability to clone itself. Do to this cloning nature in their native region they are highly invasive. The common hyacinth is known to double their population in a couple of weeks.
Water Lettuce, Hardiness Zone 8-10 (Pistia). It is a perennial with thick, soft leaves that form a rose like shape or rosette. It floats on the surface of the water, its roots hanging submersed beneath floating leaves. The leaves can be up to 14 cm long and have no stem. They are light green, with parallel veins, wavy margins and are covered in short hairs which form basket-like structures which trap air bubbles, increasing the plant’s buoyancy. The flowers are hidden in the middle of the plant amongst the leaves. Small green berries form after successful fertilization. The plant can also undergo asexual reproduction. Mother and daughter plants are connected by a short stolon, forming dense mats. These plants are illegal in some states.
Water-clover, Hardiness zone 5-10 (Marsilea). These small plants are of unusual appearance and do not resemble common ferns. Common names include water clover and four-leaf clover because the long-stalked leaves have four clover-like lobes and are either held above water or submerged. The leaves provide shelter for pond fish and help regulate water temperature.
Water-spangle, Hardiness Zone 7-10 (Salvinia). Native to South America these small, floating plants have become a popular addition to ponds and water gardens across the United States. Water-spangles have creeping stems, branched, bearing hairs on the leaf surface but no true roots. They only grow in calm or still fresh water. These plants are only about an inch long but can grow to about 4 inches. Don’t let their small nature fool you they can cover small ponds in weeks with a dense matt like cover so attention is required to thin its growth. They reproduce through spores and can live in very dry climates and can mature very quickly with a small rain.
Duckweed or water lens, Hardiness Zone 4-10 (Lemnoideae). These plants are a seed bearing, flowering aquatic plant which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Duckweed only have one to three leaves or fronds, and are very small only growing to around an eighth of an inch. Duckweed is highly invasive so be cautious when introducing it into your pond or water garden.