FIELD BOOK OF PONDS AND STREAMS 



Water-plantains and Arrowheads — Alismacece 



These are border-line plants, which are very adaptable to 

 a changing water supply and show a consequent variation 

 in the form of their leaves. The flowers have 3, often con- 

 spicuous, white petals; pistils and stamens may be in the same 

 flower, in different ones on the sam€ plant, or on different 

 plants. 



Broad-leaved arrowhead, Sagittaria latifolia. — Arrowheads 

 grow on wet shores or in shoal waters in company with bur- 

 reeds and bulrushes, pickerel- weed, and water-plantains 

 (PI. X). Broad-leaved arrowheads (Fig. 63) are 6 to 24 

 inches high with dark green arrow-shaped leaves and deli- 

 cate, 3-petaled white flowers which are arranged in whorls 

 of threes with the pistillate or female flowers in the lowest 

 cluster. The shape of the leaves in this and other species 

 varies with the depth of water and, in lakes, with their ex- 

 posure to the action of waves. Plants which grow in deeper 

 water usually have narrower leaves, but narrow and broad 

 leaves are often found on plants only a few inches apart. 

 Arrowheads adapt themselves to either droughts or floods 

 and when submerged they develop narrow ribbon-like leaves. 

 A single plant sometimes has a few narrow grass-like leaves, 

 some broadly ribboned ones, and still others which are arrow- 

 shaped. If a drought has left the plant stranded without water, 

 the narrow water leaves fall off and broad arrow-shaped ones, 

 better suited to work in the air, gradually take their places. 

 Adjustments like these are very common in all the arrow- 

 heads and they live in or out of water with all the ease of frogs. 



Occurrence. — This and other species all grow on the margins 

 of quiet streams or in the protected bays of ponds and lakes. 

 Blooms July-August. Very common throughout the eastern 

 states. 



Animal associates. — Arrowheads are pollinated by water 

 insects, mainly by damselflies and dragonflies which keep 



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