14 



1. Egeria densa Planch. Fig. 6, Map 7 



Rare plant of ponds in New England. This common aquarium 

 plant has been introduced into North America from South America. 

 Cold weather does not seem to adversely affect it once introduced into a 

 pond. Populations are occasionally established at widely scattered 

 areas, reproducing vegetatively. Occurring sporadically from Ver- 

 mont and Massachusetts west to Illinois, Nebraska, Kansas, Oklaho- 

 ma, south to Florida and Texas; Arizona, California, and Oregon. 



Elodea (Waterweed) 



Submersed perennial plant of streams, ponds and lakes; leaves in 

 whorls of 3 (or 2), along the stem; dioecious or monoecious; flowers with 

 3 sepals and 3 petals; staminate flowers with the filaments united into 

 a short column; pistillate flowers raised to the surface by an elongated 

 hypanthium or sessile, but on maturity breaking loose, floating to the 

 surface where buds open and the sepals diverge; fruit leathery, ovoid 

 capsule, few seeded. 



Key to Species 



1. Leaves generally 0.3-1.5 mm wide, pointed at tip (fig. 7B), not dense- 

 ly overlapping toward stem apex (fig. 7A); staminate flowers en- 

 closed in sessile spathes, released, floating to the surface at anthesis. 



1. E. nuttallii 



1. Leaves generally 1.0-5.0 mm wide, blunt at tip (fig. 71), not densely 

 overlapping at tip (fig. 7F); staminate flowers enclosed in stalked 

 spathes, reaching the surface at anthesis by elongation of hypan- 

 thium. 

 2. E. canadensis 



1. Elodea nuttallii (Planch.) St. John Fig. 7, Map 8 



Common in acidic to moderately alkaline water of streams, lakes, 

 and ponds in New England. Range extends from northern Maine and 

 southern Quebec west to Idaho, south to North Carolina, Mississippi, 

 Oklahoma, and New Mexico. 



alkalinity: mean 23.5 mg/1; range 5.0-108.5 mg/1; (38) 

 pH: mean 6.9; range 5.6-8.9; (36) 



