pondweed

Short definition from Wiktionary

Noun

1. 1
   Any of several plants that grow in ponds or similar aquatic conditions: Potamogeton, a diverse and worldwide genus
2. 2
   Any of several plants that grow in ponds or similar aquatic conditions: Elodea, found in North America
3. 3
   Any of several plants that grow in ponds or similar aquatic conditions: Azolla, of cosmopolitan distribution
4. 4
   Any of several plants that grow in ponds or similar aquatic conditions: Aponogeton, in Africa, Asia and Australasia
5. 5
   Any of several plants that grow in ponds or similar aquatic conditions: opposite-leaved pondweed, Groenlandia densa, only plant of its genus, found chiefly in the Mediterranean region.
6. 6
   Charales, an order of green algae