Vegetative key to the families
Submerged plants rooted in mud. Leaves submerged or floating on the surface or sometimes the leaf blades held erect above the water surface. Freshwater or marine (Amphibious plants are not included in this group) Either; leaves alternate on an elongated stem (sometimes opposite when subtending flowers); or, leaves tufted on a short stem or arising from a rhizome Leaves compound finely dissected or lobed (sometimes linear and stem-clasping) Burr not formed around the fruits at maturity Florets all tubular or filiform and tubular (Fig. 41) or; florets with ligule present but the ligule less than 3mm