Illinois pondweed – Potamogeton illinoensis
Illinois pondweed is a submersed plant that has both submersed and floating leaves. Rooted to the bottom, it grows in shallow or deeper waters. Illinois pondweed grows equally well in swift-flowing rivers or quiet lake margins. This common native grows throughout Florida and blooms from spring to fall. In the field, Illinois pondweed may first be noticed by its floating leaves, and erect, green spikes of flowers or seeds. The leaves are more or less elliptic in shape, and are much longer than they are wide. They typically grow to 8 inches long. The leaves are on long leaf stems, or petioles. Illinois pondweed flowers are on spikes that are 1 to 3 inches long. The spikes are held above the water on thick, fleshy stalks. The flowers are small and green, and arranged in whorls along the length of the spike.
This native plant has
- long, narrow submersed and floating leaves
- leaves are elliptic and pointed
- produces thick spikes of greenish flowers, which are held above the water.
Illinois pondweed is a common submersed plant. Illinois pondweed grows equally well in shallow ponds, lakes, and slow-movieng rivers from the peninsula west to the central panhandle of Florida (Wunderlin, 2003). It blooms from spring to fall.
Illinois pondweed has two primary leaf shapes: the floating leaves are more-or-less elliptic in shape, and are much longer than they are wide; typically to eight inches long. The leaves are on long leaf stems or “petioles”. The submersed leaves are about the same size, but are more lance-shaped. Submersed leaves have pointed tips and pointed bases. Illinois pondweed’s greenish flowers are on spikes that are one to three inches long.
For brief control information, see Efficacy of Herbicide Active Ingredients Against Aquatic Weeds by K. Langeland, M. Netherland, and W. Haller.