가래과 Potamogetonaceae

1. 꽃은 양성이다.

2. 수술은 2 개이고 약격은 화피처럼 되지 않는다   ··························································································6. 줄말

2. 수술은 4 개이고 약격은 화피처럼 넓어진다 ······························································································· 가래속

1. 꽃은 단성이며 1 가화로서 수술은 1 개이다   ·································································································7. 뿔말

가래속 Potamogeton LINN.

1. 잎의 기부는 턱잎과 붙지 않았고 잎집은 분명하지 않디-

2. 물 위에 뜬 잎이 있다.

3. 물 위에 뜬 잎은 길이 5cm 이상， 너비 2cm 이상이다.

4. 수중엽은 산형이며 꽃이 펼 때 대개 잎새가 없어진다. 씨방은 4 개이다  ····················································8. 대동가래

4. 수중엽은 피침형이며 잎새가 있다.

5. 씨방은 4 개이며 뜬 잎의 잎자루 끝은 넓어져서 불결 같은 가장자리로 된다   ·············································9. 선가래

5. 씨방은 4 개이며 뜬 잎의 잎자루는 물결같이 되지 않는다   ····································································10. 가래

3. 잎은 작고 선형이며 길이 3cm 이하， 너비 12mm 이하이다.

6 열매의 뒷면은 밋밋하거나 둔한 톱니가 있다. 암술대는 짧고 지하경이 없으며 수중 엽은 길이 3-4.5 cm 이다  ·······11. 애기가래

6. 열매 뒤에 닭벼슬 같은 돌기가 있다. 암술대는 가늘고 길며 지하경이 있고 수중엽은 길이 4~6cm 이다   ·············12. 가는가래

2. 잎은 모두 물에 잠겨있다.

7. 잎은 피침형이고 너비 7~30mm이다.

8. 잎자루가 없거나 거의 없으며 둔두 또는 예두로서 돌기가 없다.

9. 잎의 밑부분은 줄기를 감싼다    ·······························································································13. 넓은잎말

9. 잎은 줄기를 감싸지 않는다     ·····································································································앉은가래

8. 잎자루가 있으며 길이 2~7cm 이다································································································14. 대가래

7. 잎은 선형 내지 실같이 가늘고 너비 1-6mm이다.

10. 잎에 톱니가 있고 너비 4~7mm 이며 밑부분은 줄기를 감싼다 ··································································15. 말즘

10. 잎은 밋밋하고 너비 1~3mm이다.

11. 잎은 너비 2~3mm로서 예첨두이고 열매는 길이 3.5mm이며 지하경이 있다  ················································ 16. 말

11. 잎은 너비 1 ~1.5mm로서 예두이고 열매는 길이 1.8mm이며 지하경이 없다··············································· 17. 실말

1. 잎의 밑부분은 턱잎과 붙어서 긴 잎집으로 되었으며 잎은 모두 물속에 들어있다.

12. 잎은 너비 2~3mm로서 둔두이고 잔톱니가 있다 ···················································································18. 새우가래

12. 잎은 너비 1mm로서 예두이고 가장자리가 밋밋하다       ·········································································19. 솔잎가래