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Embryo hooked, annular, or cochleate, the radicular end pointing downward.—Herbs of fresh, or one in brackish, ponds and streams, with jointed mostly rooting stems, and 2-ranked leaves, which are usually alternate or imperfectly opposite; the submersed ones pellucid, the floating ones often dilated and of a firmer texture.

Embryo straight, the radicular end downward.—Slender branching herbs, growing under water, with opposite and linear leaves, somewhat crowded into whorls, spinulose-toothed, sessile and dilated at base.

Cotyledons long and narrow, incumbently folded transversely, i.e., the cleft extending to the radicular side of the curvature.

The radicular extremity points towards the micropyle, while the cotyledonary extremity is pointed towards the base of the ovule or the chalaza.