Flower:

100+ short-stalked flowers along a stout, naked stem in a narrow, spike-like raceme 8 to 16 inches long, often densely clustered at the tip end and more sparsely below. Individual flowers are globular, about 1/8 inch long, with a dense feathery cluster of white to purple hair-like stigmas at the top. 6 fleshy, oval tepals (petals and similar sepals) surround the base and hide the stamens. Tepals are hairless and green to purplish. Each plant has multiple flowering spikes that emerge and grow throughout the growing season. Spikes are usually straight but may bend and twist some, and do not elongate much more in fruit than when flowering.

Leaves and stems:

Leaves are mostly basal, erect to ascending, dark green, toothless, hairless, up to 16 inches long but usually much shorter than the flowering stems, blunt or pointed at the tip, slender and semi-circular in cross section with a groove down the center towards the base.

Near the base of the blade is a ¾ to 1-inch long sheath, white and membranous, often 2-lobed at the tip, hood-like around the next inner blade. Flowering stems are smooth and often reddish or purplish. 

Fruit:

Fruit is green and oblong, about 1/8 inch long, divided into six evident carpels, the margins obscurely winged and the withered styles persistent at tip.

Notes:

Seaside Arrowgrass is relatively common in shallow, brackish to freshwater marshes, open wet prairie and even road ditches throughout the northern 3/4 of Minnesota. It is not a grass at all, though is noted as a graminoid (grass-like) growth habit at USDA, but is distantly related to such diverse species as Jack-in-the-pulpit (Araceae family) and pondweeds (Potamogetonaceae). It is far more common than Minnesota's other arrowgrass, Marsh Arrowgrass (Triglochin palustris), which is mostly restricted to alkaline fen habitats in the western half of the state. Marsh Arrowgrass is much smaller in size and structure and, even when growing side-by-side with its larger cousin, it is often obscured by surrounding vegetation. Both, however, produce an objectionable musky skunk-like odor when crushed, contain cyanide and are poisonous to livestock as well as humans.