Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.
1 Lower side of the midvein of the leaves prickly; internodes prickly; leaves coarsely and raggedly serrate, the tooth sinuses often halfway or more to the midvein; plants dioecious; [subgenus Najas]
1 Lower side of the midvein of the leaves smooth; internodes smooth; leaves more finely serrate, the tooth sinuses < 0.2× of the way to the midvein; plants monoecious; [subgenus Caulinia].
..2 Leaf-teeth multicellular, evident at 10× magnification, 5-22 per side; leaves either ascending to spreading, or becoming recurved late in the season; seed-coat pitted.
....3 Style offset to the side of the seed apex; [section Caulinia]
..2 Leaf-teeth unicellular, not or barely evident at 10× magnification, 18-100 per side; leaves spreading to ascending; seed-coat smooth or pitted, the areoles (if present) longer than wide or about as long as wide; [section Americanae].