Flower:

Slender spike-like raceme 4 to 8 inches long, extending up to 12 inches in fruit, with 15 to 80 short-stalked flowers usually sparsely arranged along the very slender stem. Individual flowers are globular to somewhat oblong-conical, 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.

Leaves and stems:

Leaves are mostly basal, erect to ascending, dark green, up to 12 inches long but usually shorter than the flowering stems, slender, pointed at the tip and semi-circular in cross section with a groove down the middle towards the base. Near the base of the blade is a 1 to 2-inch long sheath, white and membranous, not lobed at the tip. Flowering stems are smooth and often reddish or purplish.

Fruit:

Fruit is a yellowish green, slender capsule about 1/3 inch long on a slender, erect stalk, blunt and broadest at the tip with a long slender taper to the base, appearing to be three parted from a 3 winged axis.

Notes:

Marsh Arrowgrass is relatively uncommon in Minnesota, being mostly restricted to alkaline fen habitats in the western half of the state. It is not a grass at all, though is noted as a graminoid (grass-like) growth habit at USDA, but is distantly related such diverse species as Jack-in-the-pulpit (Araceae family) and pondweeds (Potamogetonaceae). Seaside Arrowgrass (Triglochin maritima) is more widespread and locally abundant, and can be found side-by-side with T. palustris in these fen habitats. Seaside Arrowgrass is easily distinguished by its shear size and more robust structure and can be somewhat distracting of its much smaller and petite relative. Both however produce an objectionably pungent odor when crushed, contain cyanide toxic to livestock, and can often be smelled before they are seen. While one reference notes T. palustris may have up to 80 flowers in a cluster, we've typically seen 20 or fewer on a single stem.