noun, noun which may take the genitive case particle 'no'
algae; waterweed; seaweed; duckweed
Broad term for aquatic plants and algae, from microscopic algae to large seaweeds and freshwater duckweed. Often used in compound words.
池の水面に藻が浮いている。
Algae is floating on the surface of the pond.
海岸に打ち上げられた藻を集めた。
We collected the seaweed washed up on the shore.
海藻 specifically refers to marine algae or seaweed, while 藻 is a broader term that includes freshwater algae and duckweed.
水草 is a general term for aquatic plants, including vascular plants, whereas 藻 typically refers to algae and similar non-vascular organisms.
The kanji 藻 is a phono-semantic compound with 艹 (plant) and 喿 (sound). The reading も is the native Japanese word for algae and aquatic plants.