Plant of the Week
Range map of Justicia americana. States are colored green where the species may be found.
Whole plant. Photo © 2012 David D. Taylor.
Close up of flowers. Photo © 2012 David D. Taylor.
Plants in habitat. Photo © 2012 David D. Taylor.
American Water Willow (Justicia americana (L.) Vahl.)
By David Taylor
American water willow is in the Acanthaceae (Acanthus) family. This family contains about 2,500 species worldwide that range from herbs to shrubs and small trees. Most are tropical. Members of this genus are most common in the tropics, but a few are found in the United States. This species is found from Texas, Oklahoma, Kansas, Iowa, and Michigan east to New York and Vermont, south to Florida. It also occurs in northern Ontario and Quebec.
American water willow grows from slender rhizomes which over time can produce large colonies of about 90 square meters (1,000 square feet) or more. Stems may be 50 - 100 centimeters (1.6 - 3.3 feet) high. The leaves are simple, about 8 - 16 centimeters (3 - 6 inches) long and about 8 - 25 millimeters (1/3 - 1 inch) wide. Flowers are produced in small clusters on stalks from the axils of leaves. They are white and purple and about 1.3 centimeters (1/2 inch) across. There are prominent bee guidelines in the center of the flower. Flowering begins in June and may continue to September depending on location.
The common name comes from a resemblance of the leaves to willow leaves and the fact that it grows in water. Typical habitat is in shallow riffles (at least summer time) in large streams and rivers. It is usually abundant in these locations. It is pollinated by bees and butterflies.