noun
hydrilla; Hydrilla verticillata
A common aquatic plant, often found in ponds and slow-moving water. The scientific name is Hydrilla verticillata.
池にクロモがたくさん生えている。
A lot of hydrilla is growing in the pond.
noun
Papenfussiella kuromo
A species of brown algae. This is a less common, more technical usage.
クロモの一種に、Papenfussiella kuromo と呼ばれる褐藻がある。
One type of kuromo is a brown algae called Papenfussiella kuromo.
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.