Much like no. 9 [Myriophyllum sibiricum Kom.]; stem thickened below the infl to almost double its width farther down, curved to lie parallel with the water-surface, usually branching freely near the water-level; shoot-tip more tassel-like, with internodes mostly 1-3 cm; no turions; lvs with more numerous (mostly 12-20) long, straight segments per side; lower bracts often pectinate and often somewhat exceeding the frs; mericarps 2-3 mm; 2n=42. European sp., widely intr. in N. Amer., tolerant of nitrogenous pollution.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.