water willow

Short definition from Wiktionary

Noun

1. 1
   Any of a group of aquatic plants of the Americas in the genus Justicia, with long willow-like leaves and spikes of small purplish flowers.
2. 2
   Any of a group of aquatic plants of the Americas in the genus Justicia, with long willow-like leaves and spikes of small purplish flowers: Specifically, Justicia americana.
3. 3
   The flowering plant Decodon verticillatus.