Myriophyllum is a genus of the family Haloragaceae, and it contains approximately 45 freshwater aquatic plants. The name of this genus is derived from two Latin words, where myrio means too many to count, and phyllum means leaf. Most of the plants of this genus have whorl-like leaves that are not of a homogeneous texture. On the upper part of these plants, the leaves are firmer and smaller in size compared to the limp leaves further down. The flowers are commonly small, with four petals, and can be seen above the water surface in ponds.
Species of Myriophyllum, or water milfoil, are found all over North America and generally grow in slow moving, almost still water. Their flowers bloom above water from June until September, while the leaves remain below the surface. These plants can be used as a cellulose feed stock for bio-oil refineries.
One species of water milfoil is the Myriophyllum spicatum, also known as the spiked water milfoil. This species is sometimes considered to be a menacing pest rather than a harmless plant owing to its dominating and over-powering characteristics. It can take over an entire area, leaving no room for other floral plantation. Myriophyllum spicatum is often placed in aquariums as filler. Regular pruning is recommended so that it does not completely fill up the aquarium.
Another species of Myriophyllum is the verticillatum, or whorled water milfoil. This plant spreads over a large area and is found in both the United States and the United Kingdom. It is an invasive aquatic plant that is quite similar to the other invasive species of Myriophyllum, such as Eurasian water milfoil, hybrid water milfoil, and parrotfeather water milfoil. The whorled water milfoil grows in shallow ponds, marshes, and lakes. This species is an excellent oxygenator in ponds, giving protection and respiratory aid to fish spawn.
Parrotfeather, or Myriophyllum aquaticum, is another popular species native to the Amazon River in South America, but can now be found in both warm and cold climate areas. It was introduced to North America in the late 1800s. Though it is usually located in freshwater ponds and streams, this plant has great compromising capabilities and can adapt to fast-moving water conditions. Parrotfeather is often considered attractive and is therefore preferred in cultivation over other species of the genus. It is very easy to cultivate and can be planted through fragmentation as well as intentional planting.