12 



to Ontario, Michigan, Wisconsin, and British Columbia, south to 

 Florida, Oklahoma, Texas, Washington, and California; Mexico, 



alkalinity: mean 60.0 mg/1; range 12.0-102.5 mg/1; (16) 



pH: mean 7.8; range 6.7-10.2; (16) 



9. Myriophyllum exalbescens Fern. Fig. 6, Map 10 



Scattered in alkaline regions of New England with the largest 

 populations in Aroostook County, Maine, western Vermont, and 

 western Massachusetts. This taxon has long been included as a 

 variety under Myriophyllum spicatum L. in the United States. While 

 both species occur in New England, the native M. exalbescens 

 appears to be on the decline in areas where non-native M. spicatum 

 occurs. Aiken et al. ( 1979) indicate a good character to distinguish the 

 two species is that the vegetative stem apices of M. spicatum. appear 

 tassel-like and are usually red, while those of M. exalbescens are 

 knob-shaped and generally lack the reddish color, except during the 

 time of winter bud formation. Range extends from Newfoundland 

 and southeastern Labrador west to Alaska, south to Nova Scotia, 

 New England, West Virginia, Michigan, and northwestern Kansas. 

 Plants collected south of the 0°C isotherm are likely to be M. spicatum 

 (Aiken, 1981), thus records from Texas, New Mexico, Arizona, and 

 southern California need reexamination. 



alkahnity: mean 57.4 mg/1; range 13.5-123.5 mg/1; (19) 



pH: mean 7.8; range 6.8-9.8; (18) 



Proserpinaca (Mermaid Weed) 



Submersed in shallow waters or emergent along shores of ponds, 

 lakes, and streams; growing from slender creeping roots; leaves alter- 

 nate, pinnatifid to serrate; flowers sessile in leaf axils, solitary or 2-5; 

 fruit 3-angled, 3-seeded, nut-like. 



Key to Species 



1. Leaves of emersed plants serrate or serrate to deeply pinnatifid to 

 pectinate (fig. 7A,B); submersed leaves divided, (fig. 7A). 



1. P. palustris 



1. Leaves of emersed plants all pectinate (to divided), never serrate 

 (fig. 7D); submersed leaves divided (fig. 7E). 

 2. P. pectinata 



