pickerelweed, common name for the Pontederiaceae, a family of chiefly tropical perennial aquatic herbs found in freshwater. The pickerelweeds (genus Pontederia ) range north into temperate regions, including most of the E United States and Canada. The water hyacinth ( Eichhornia crassipes ), a native of tropical America, has spread widely and is so prolific that it has clogged many waterways in the S United States and in other areas, including Java, Australia, and the Great Lakes region of E Africa. It is sometimes cultivated in tanks and ponds for its ornamental foliage and blue-violet flowers. The pickerelweed family is classified in the division Magnoliophyta, class Liliopsida, order Liliales.