Submersed Plants

 
Species: Heteranthera dubia (Jacq.) MacMillan, water star-grass
Family: Pontederiaceae

Water star-grass is an attractive underwater plant, with small star-shaped yellow flowers that float or rise just above the water surface. The dark green leaves are long, grass-like, and arranged alternately on long branching stems. These plants frequently grow into large tangled masses in shallow water or stranded along shorelines.

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Leaf: Narrow (2-6 mm wide), 10-15 cm long, deep green, grass-like leaves lack a distinct midvein. The base of the leaf is joined to a tubular sheath which wraps around the stem. The sheath has a membranous extension, rounded at first, but becoming divided with age. 

Stem: The slender, branching stem is round or slightly flattened in cross section. The stem grows to 2 m, is more or less limp, and often forms profuse roots at the nodes.

Flower: Bright yellow, tubular flowers have 6 "petals" (tepals) that form a star and rise just above the water surface. The flower tube is long and narrow and the tepals are 5 mm long. Flowers sometimes don't open, self-pollinating in the bud instead. Water star-grass flowers infrequently in the Pacific Northwest.

Fruit: The fruits are oval capsules up to 1 cm long, containing several longitudinally ridged seeds.

Root: The roots are fibrous and grow from rhizomes. The stems often form roots at the nodes.

Propagation: Water star-grass spreads from seeds dispersed by water and from rooted stem fragments.

Importance of plant: Waterfowl eat the foliage. Water star-grass provides fish cover and good habitat for invertebrates and the grass-like leaves especially appeal to ducks.

Distribution: North and Central America. In Washington, water star-grass is found mostly in the central and eastern part of the state. 

Habitat: Water star-grass grows in shallow water up to 1 m deep, including slow streams, rivers, lakes, and ponds. It can survive on mud banks and is tolerant of alkaline water.

May be confused with: Non-blooming, narrow-leaved pondweeds (Potamogeton spp.), such as flat-stem pondweed (P. zosteriformis), sago pondweed (P. pectinatus), or flat-stalked pondweed (P. friesii). Water star-grass can be distinguished from the pondweeds by the lack of a prominent midvein in the leaves.

Photographs: Heteranthera dubia closeup showing flowers

Line Drawings: Heteranthera dubia


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