Flower:

Stalked flowers are whorled in open clusters on many branches coming off the main stem. Individual flowers are ¼ to 1/3 inch across, 3 pale pink to purplish petals with a spot of yellow-green at the base. In the center are 6 yellow-tipped stamens surrounding a ring of up to 20 green pistils.

Behind the flower are 3 green to brown sepals up to about half as long as the petals. At the base of a whorl of flowers are 3 papery bracts shorter than the flower stalks. When plants are under water, flowers are self-pollinating and do not open (cleistogamous).

Leaves and stems:

Plants are aquatic, growing in shallow water, but also on shores or becoming land-locked when water recedes. Leaves can take on different forms depending on the water level—submersed, floating or emersed—but all are in a basal rosette. Submersed and floating leaves are thin, ribbon-like, up to 3 feet long, up to about ½ inch wide, and stalkless. Emersed leaves are long-stalked with a lance-linear to narrowly lance-elliptic blade up to about 2½ inches long and ½ inch wide. Flowering stems are erect and smooth.

Fruit:

Fruit is a ring of seeds 1/8 to ¼ inch in diameter that turns from green to brown as seeds mature. Seeds are 1.8 to 2.7 mm long, oval to round, with a pair of shallow grooves flanking a ridge along the outer edge, and a curved tip on the inner edge, remains of the style forming a short, erect beak.

Notes:

There are 3 species of Water-plantain in Minnesota, Alisma gramineum being the least common. According to the DNR, aquatic plant surveys conducted at over 2,000 lakes over the past 20+ years have only located 16 populations of this species, none of the few recorded pre-1960s have been relocated, and it is not expected many more will be found. The species is at risk from habitat degradation from a variety of sources, including pollution, recreational activities, shoreline erosion and agricultural run-off. Alisma gramineum was listed as a Special Concern species in 2013.

It is distinguished from the other Alisma species in Minnesota by its narrower leaves, pinkish flowers, and ribbon-like leaves when submersed (note: the aquarium plant database Barr Report has an image of submersed leaves). A. subcordatum and A. triviale both have much larger leaf blades (to 7 inches long, 3 inches wide), lack different submersed leaves even when growing in shallow water, and have consistently white flowers. Water-plantain flowers are also similar to Arrowhead, but Arrowhead flowers are much larger—½ to 1 inch across.