ALISMACEAE. 17 



Family 14. ALISMACEAE. 



Aquatic or marsh herbs with fibrous roots, scape-like stems and 

 basal long-petioled leaves; inflorescence a raceme or panicle; 

 flowers regular, perfect, monoecious or dioecious, pedicelled ; the 

 pedicels whorled and subtended by bracts; sepals 3, persistent; 

 petals 3, deciduous; stamens 6 or more; ovaries numerous or 

 rarely few, 1-celled, usually 1-ovuled; carpels becoming akenes 

 in fruit; endosperm none. 



Carpels in a ring upon a small flat receptacle; leaves 



ovate (in ours). 28. Alisma, 17. 



Carpels crowded in many series upon a large convex re- 

 ceptacle; leaves sagittate (in ours). 29. Sagittaria, 17. 



28. ALISMA. 



Perennial or rarely annual herbs with erect or floating leaves; 

 inflorescence a panicle or umbel-like panicle; flowers perfect, 

 small, numerous, on unequal 3-bracted pedicels; petals small; 

 stamens 6 or 9; ovaries few or many, more or less in one whorl 

 on a small flat receptacle. 



Alisma plantago-aquatica L. Water Plantain. Scapes stout, 30-100 cm. 

 tall; leaves all radical, erect or floating, the petioles usually long; the blades 

 ovate or oblong, acute, rounded or subcordate at the base, 5-15 cm. long, 5-7- 

 nerved; flowers in a large panicle composed of 3-6 whorls of branches, these 

 again branched once or twice; flowers on pedicels 1-5 cm. long; petals white, 

 hardly exceeding the sepals; akenes obliquely obovate, compressed, arranged 

 in a circle on the receptacle. Common in ponds and wet places. 



29. SAGITTARIA. Arrowhead. 



Perennial aquatic or marsh herbs with basal long-petioled 

 leaves; flowers monoecious or dioecious, borne near the summits 

 of the scapes in whorls of 3, the staminate usually uppermost; 

 petals usually conspicuous; stamens usually numerous; ovaries 

 numerous, crowded in globose heads. 



Petioles short, usually curved; bracts 8-20 mm. long; usually 



terrestrial. 5. arifolia. 



Petioles long and slender; bracts 4-6 mm. long; aquatic. 5. cuneata. 



Sagittaria arifolia Nutt. Terrestrial or rarely aquatic, 10-50 cm. tall; 

 petioles stout, ascending, 10-30 cm. long; blades 6-18 cm. long, sagittate, 

 acute, the basal lobes diverging and usually much smaller than the terminal 

 one; sepals becoming reflexed; petals white; fruiting head globose, 8-15 mm. 

 in diameter; akenes 2 mm. long, obovate-cuneate, much flattened, with a 

 minute erect beak. Common on the margins of ponds and streams. 



Sagittaria cuneata Sheldon. Submerged aquatic; petioles long and slender; 

 blade floating, the lobes narrow; inflorescence scarcely raised above the water; 

 fruiting head 10 mm. in diameter; akenes 1 mm. long. Phiieo Lake, Suksdorf. 

 This is probably only an aquatic form of S. arifolia. 



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