water-shield
Brasenia schreberi latin

B. nymphoides, B. peltata) has the common name water-shield (also watershield or water shield).

Cabomba caroliniana (fanwort; Carolina water-shield)

Although everyone's mood began to clear along with it, and Jill was as glad as anyone at the prospect of getting dry, still she felt uneasy without their water-shield around them.