ALISMATACEAE 



1. Pistils in a single ring on a flat receptacle (figs. 1, 2); flowers all 

 perfect, stamens 6. 



1. Alisma 



1. Pistils in a dense globose head (figs. 4E, lOD); flowers perfect or 

 imperfect, stamens more than 6. 

 2. Flowers perfect; achenes plump, conspicuously ridged, not winged 



(fig. 3C); leaf blade never sagittate; roots not septate. 



2. Echinodorus 



2. Flowers imperfect, uppermost flowers mostly staminate (fig. lOA) 



or plants dioecious; achenes flattened, winged, not ridged (figs. 



lOE, 12C, 14D); leaf blade often sagittate; roots septate (fig. 4A, 



6A, 9A). 



3. Sagittaria 



Alisma (Water-plantain) 



Plants of shores and marshes, often submersed in water up to one 

 meter in depth; growing from corm-like rootstalks; leaves all basal, 

 ribbon-like, ovate or elliptical; flowers perfect, borne in a panicle; fruit 

 an achene, borne in a circle on a flattened receptacle. 



Key to Species 



1. Leaves submersed and ribbon-like (fig. IB) or if emersed, lanceolate 

 to narrowly elliptic, 0.5-2.0 cm broad (fig. lA); achenes with two 

 dorsal grooves and a central ridge (fig. IE). 



\. A. gramineum 



1. Leaves emersed with ovate to elliptic blades (fig. 2A); occasionally 

 submersed or floating (fig. 2B), up to 15 cm broad; achenes with 

 single dorsal groove (fig. 2F). 

 2. Flowers 7.0-13.0 mm broad; sepals at anthesis 3.0-4.0 mm long; 



petals 3.5-6.0 mm long; fruiting heads 4.0-7.0 mm in diameter; 



achenes 2.2-3.0 mm long. 



2a. .4. plantago-aquatica var. americanum 



2. Flowers 3.0-3.5 mm broad; sepals at anthesis 2.0-2.5 mm long; 



petals 1.0-2.0 mm long; fruiting heads 3.0-4.0 mm broad; achenes 



1.5-2.0 mm long. 



, . . . . 2h. A. plantago-aquatica var. parviflorum 



