Plant: perennial, rhizomes ± slender, not thickened at tip; stems erect, 2-8 dm, generally glabrous; nodes short-hairy Leaves: 2-8(10) cm, short-petioled, oblong to lanceolate, lobed to cut especially in lower half, glabrous to puberulent on veins INFLORESCENCE: cyme, axillary, each head-like, subtended by leaves Flowers: calyx 5-lobed, lobes awl-like, short-awned; corolla 2-3 mm, ± = calyx, white; stamens 2, exserted, staminodes 2, minute, club-shaped; style exserted Fruit: nutlets 4, 1-1.5 mm, top rounded, smooth, ± compressed, edge corky-thickened Misc: Moist areas, marshes, streambanks; < 1000 m.; Aug-Sep