Ceratophyllaceae, the Hornwort Family
Submerged aquatics, with whorled, finely dissected leaves and inconspicuous flowers with neither calyx nor corolla.
One species in Michigan Hornwort, Ceratophyllum demersum.
Nymphaeaceae, the Water Lily Family
Aquatic plants, with usually large and floating leaves which are round or elliptical and palmately veined.
| 1a. Floating and emersed leaves centrally peltate — 2. | |
| 1b. Leaves rounded but not peltate, with a deep sinus — 3. | |
| 2a. Leaves round, 3 dm. in diameter or more; flowers very large, pale yellow | Lotus, Nelumbo lutea. |
| 2b. Leaves oval, 5-15 cm. long; flowers small, purple | Water Shield, Brasenia schreberi. |
| 3a. Flowers yellow (Pond Lily) — 4. | |
| 3b. Flowers white or tinged with pink (Water Lily) — 5. | |
| 4a. Leaves more than 1 dm. long | Pond Lily, Nymphaea advena. |
| 4b. Leaves less than 1 dm. long | Pond Lily, Nymphaea microphylla. |
| 5a. Flowers very fragrant; leaves purplish beneath | Water Lily, Castalia odorata. |
| 5b. Flowers not fragrant; leaves green beneath | Water Lily, Castalia tuberosa. |