Myriophyllum

Myriophyllum (water milfoil) is a group of about 69 types of plants that grow in freshwater. These plants can be found all over the world, but Australia has the most different kinds, with 43 special to that area.

These plants usually have long stems with special tubes for air and leaves that grow in circles around the stem. The leaves are often finely split, but this can vary. Some North American kinds, like M. tenellum, have leaves arranged one after another and look more like tiny scales. In many species, the leaves above the water are different from those below — stiffer, smaller, and sometimes not split at all.

These plants can have flowers that contain both male and female parts, or they can have separate male and female plants. Their flowers are tiny, usually with four parts, and grow where the leaves meet the stem. The fruits of these plants break apart into small sections when they are ready, and they, along with the leaves, can be eaten by birds that swim. These birds likely help spread the plants by carrying seeds or pieces to new places.

Invasion and control

Three types of water milfoil plants have spread quickly in lakes, rivers, and canals in North America. Many areas have created plans to manage these plants.

People have tried different ways to control water milfoil. Some have used special chemicals, while others have tried to block sunlight with water lilies. Machines like lake mowers can help, but the plants can grow back from small pieces. Tools like lake rakes can also be used, similar to doing lawn work. There are even special machines that work automatically.

One effective method uses a small insect that only eats water milfoil. Since around the year 2000, people have also used careful hand-picking to manage these plants. While it’s hard to remove them completely, regular work by trained divers can keep the plants at lower, more manageable levels.

Taxonomy

Scientists studied the family tree of water milfoil plants and found that another small group of plants, once thought to be lost, actually belongs inside water milfoil. This helped organize water milfoil into three main groups.

Some well-known types of water milfoil include:

• Myriophyllum alpinum
• Myriophyllum alterniflorum
• Myriophyllum amphibium
• Myriophyllum aquaticum
• Myriophyllum artesium
• And many more others!