생이가래과 Salviniaceae

1. 뿌리가 없다. 잎은 줄기에 3 장씩 윤생하며 2 장은 물위에 뜨고 1 장은 물속에서 뿌리의 구실을 한다 ······················ 223. 생이가래

1. 뿌리가 있다. 잎은 2 장씩이며 각각 위아래 2 개로 갈라져서 위의 것은 물에 뜨고 밑의 것은 물속에서 포자낭을 생산한다 ··············· 물개구리밥속

물개구리밥속 Azolla LAMB.

1. 뿌리에 뿌리털이 있고 엽면에 작은 돌기가 있다 ·················································································· 224. 물개구리밥

1. 뿌리에 뿌리털이 없고 엽면에 돌기가 뚜렷하지 않다 ········································································ 224+. 큰물개구리밥