Alligatorweed

picture of alligatorweed closeup of foliage and flower

Alternanthera philoxeroides

Family:
Amaranthaceae

Lifecycle:
Perennial

Native or Introduced:
Introduced

Nutrient Removal Rating:
Low-Medium

Wildlife Value:picture of alligatorweed growth habit

Low

Invasiveness:
High

Rooted or Floating:
Rooted

Site Requirements:
Full sun to part shade

Maximum Water Depth:
6 inches

Plant Description:
Alligatorweed is a perennial aquatic herb that can sometimes be semi-terrestrial. It produces prostrate stems that grow laterally. Under certain conditions, the plant can be highly aggressive - leading to formation of dense, oppressive mats.

Stems are red-green and 1/4 inch in thickness.

Leaves lack petioles and are narrow and elliptical in shape. They are dark green with a lighter green midvein. Leaves are arranged opposite each other on the stem. Leaves are approximately 4 inches long.

Flowers are white and are grouped in spherical spikes that arise from leaf axils. They look similar to the white ball-like inflorescences of clover plants. The flowering season stretches from April to October.

Alligatorweed will grow in most areas where there is significant moisture. Typically it is found in lakes and streams. It may be present in small colonies of large thick mats that can cover entire bodies of water.

Sources:

  • Audlbach-Smith, C.A., deKozlowski, S.J. 1996. Aquatic and Wetland Plants of South Carolina. South Carolina Department of Natural Resources.
  • Flora of North America (see link below),

Additional reading: