a large genus of aquatic herbs found in quiet waters in temperate regions; leaves usually float on the water
例句
用作名词 (n.)
The existence of bract primordium during the early stages in many species of Potamogeton indicates that the absence of bract in mature flowers should be the result of reduction. 在花原基早期发育的过程中苞片原基的存在表明眼子菜属植物成熟花中缺乏苞片是简化的结果。