any aquatic annual or perennial plant of the genus Heteranthera of the pickerelweed family (Pontederiaceae), consisting of about 10 species, distributed primarily in tropical America. The broad or ribbonlike leaves of these plants have leafstalks that form sheaths around the long stems. Some species of Heteranthera grow below the water; others float or are rooted on muddy stream banks and lakeshores. Water star grass (H. dubia) is widely distributed throughout North America; it has yellow star-shaped flowers.