achene

Carl Linnaeus was not kidding when he chose the name Ambrosia for it: achene, its nutritious fruit, provides lots of calories to wildlife.

From Scientific American ● Sep. 9, 2011

Perennial, smooth; sheaths naked; leaves heart-shaped or slightly halberd-shaped, pointed; racemes interrupted, leafy; the 3 outer calyx-lobes strongly keeled and in fruit winged; achene smooth and shining.—Moist thickets, common.

From The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee by Asa Gray

Leaves linear to oblong-lanceolate; heads many, crowded; scales close, obtuse or the uppermost mucronate; achene smooth.—Low grounds, Ohio and Ky. to Dak., and southward.

From The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee by Asa Gray

Culms slender or filiform; tubercle narrower, acute, beak-like, sometimes half as long as the achene.

From The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee by Asa Gray

Culm continuous and sharply 4-angled; achene finely reticulated, with a conical flattened distinct tubercle.—Shallow water, central N. Y. to Mich., and southward; rare.

From The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee by Asa Gray