7. Bracts pectinate to pinnatifid (fig. 51); winter buds well- 

 formed, clavate, abscissing by early winter and readily 

 dispersed (fig. 5G). 

 6. M. verticillatum 



7. Bracts of upper portion of inflorescence serrate (fig. 5C), 

 somewhat pectinate at waterline (fig. 5D); winter buds 

 developed at the base of the stems or on rhizomes, usu- 

 ally remaining attached. 



1. M. heterophyllum 



6. Bracts usually less than twice as long as pistillate flowers. 



8. Leaves feather-like; middle leaves with 12 or more seg- 

 ments on each side of rachis (fig. 6B); ends of uppermost 

 leaves flat-topped (fig. 6B); stem diameter below inflores- 

 cence thick, up to twice diameter of lower stem; turions 

 not formed. 



8. M spicatum 



8. Leaves not feather-like, often tangled in drying; middle 

 leaves with 11 or fewer segments on each side of rachis 

 (fig. 6F); ends of uppermost leaves rounded (fig. 6F); stem 

 diameter below inflorescence same diameter as lower 

 stem; turions formed in fall. 



9. M exalbescens 



1. Myriophyllum tenellum Bigelow Fig. 2, Map 2 



Common in shallow sandy or muddy margins of ponds and lakes 

 of low alkalinity. This species occurs chiefly in the sterile submersed 

 form, flowering infrequently. Apparently tolerant of some salinity, it 

 has been observed in a coastal pond on Cape Cod, Massachusetts in 

 water with a chloride content of 1201.2 mg/1. The type locality is Fresh 

 Pond, Cambridge, Massachusetts. Range extends from Newfound- 

 land west to Ontario, Michigan, and Minnesota, south to Nova Scotia, 

 New England, Long Island, New York, and eastern Pennsylvania. 



alkalinity: mean 7.2 mg/1; range 3.0-19.5 mg/1; (6) 



pH: mean 6.6; range 5.9-7.2; (6) 



2. Myriophyllum humile (Raf.) Morong Fig. 3, Map 3 



Common, submersed or amphibious, in shallow acid waters of 

 eastern and southern New England. Extremely variable, three eco- 

 logicsd variants have been given nomenclatural recognition at the 

 forma rank. Range extends from Nova Scotia west, sparingly, to 

 Minnesota, south to New England, eastern New York, eastern Penn- 

 sylvania, and eastern Maryland. 

 Rare and endangered plant list: Vermont 



alkalinity: mean 7.0 mg/1; range 2.5-13.0 mg/1; (19) 



pH: mean 6.3; range 5.8-7.0; (19) 



