hydrilla; Hydrilla verticillata
A common aquatic plant, often found in ponds and slow-moving water. The scientific name is Hydrilla verticillata.
A lot of hydrilla is growing in the pond.
Papenfussiella kuromo
A species of brown algae. This is a less common, more technical usage.
Kuromo also has a technical usage referring to a brown alga.
Katakana spelling is common for this plant name; usually written in kana.
Kanji spelling is rare; the word is usually written in kana.
The name クロモ literally means 'black algae' (黒藻). The exact derivation is uncertain, but it likely refers to the dark color of the plant.