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FAMILY KEY 



Leaves alternate 



Plants marine or of estuaries; leaves up to 2 m long, 

 all submersed; flowers imperfect; inflorescence an 

 elongate, flattened spike, surrounded by a sheathing 

 leaf-like spathe at maturity (fig. 1A,B) . 

 Zosteraceae 



2. Plants freshwater or estuarine; leaves much less than 2 

 m long, submersed and/or floating; flowers perfect (2 

 per spike in Ruppia ) ; inflorescence a cylindric spike, 

 enveloped by stipule ( Potamogeton ) or sheathing leaf 

 base ( Ruppia ) during development, becoming exserted at 

 maturity (fig. 9A, 37A) . 

 Potamogetonaceae 



Leaves opposite, occasionally appearing whorled 



Plants perennial, rhizomes common (fig. 38A) ; leaves 

 entire, without broadened bases; flowers and fruits 

 borne on short stalks; fruits bilaterally symmetrical, 

 usually dentate (occasionally minutely spinulose) on one 

 side (fig. 38B) . 

 Zannichelliaceae 



3. Plants annual; rhizome lacking (fig. 39A) ; leaves 

 mostly serrate, with broadened, sheathing bases 

 (fig. 38B, C) ; flowers and fruits sessile; fruits 

 radially symmetrical, smooth. 

 Na j adaceae 



