자라풀과 Hydrocharitaceae

1. 심피는 6~15 개이며 태좌가 튀어나온다.

2. 꽃은 양성이며 줄기에 포복경이 없다    ·······························································································40. 물질경이

2. 꽃은 단성이며 줄기는 땅속으로 뻗어간다  ······························································································41. 자라풀

1. 심피는 보통 3 개이지만 간혹 2~4 개 또는 5 개이며 태좌는 약간 튀어나온다.

3. 잎은 나선상으로 배열한다.

4. 꽃은 양성(간혹 단성)이며 수꽃은 떨어져서 나오지 않고 밑씨는 도생한다 ······················································올챙이솔속

4. 꽃은 단성이며 수꽃은 떨어져서 나오고 밑씨는 직생한다 ··········································································38. 나사말

3. 잎은 윤생한다     ···························································································································39. 검정말

올챙이솔속 Blyxa THOUARS

1. 줄기는 길게 자라고 가지가 갈라진다. 잎은 길이 3~5cm 이고 너비 1.5~3mm 이며 꽃자루가 없다 ·························· 36. 올챙이솔

1. 줄기는 극히 짧다. 뿌리에서 돋은 잎은 길이 5-30 cm이고 너비 4~5mm이며 꽃자루는 다소 자란다.

2. 종자에 꼬리가 없다  ················································································································· 37. 올챙이자리

2. 종자는 양끝에 꼬리 같은 돌기가 있다  ······························································································37+. 올챙이풀