whorl-leaf water milfoil
A specific aquatic plant, Myriophyllum verticillatum. Botanical term; in everyday contexts, the katakana name is used.
A lot of whorl-leaf water milfoil is growing in the pond.
Katakana spelling is common for this plant name; usually written in kana.
Kanji form is rare; the word is usually written in kana.
The name フサモ likely derives from 房 (ふさ, 'tassel, tuft') and 藻 (も, 'algae, water plant'), referring to the plant's whorled leaf arrangement. The exact historical derivation is uncertain.