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1. Potamogeton robbinsii Oakes Fig. 2, Map 2 



Abundant in deep water and slow streams. The type 

 locality is Cherry Pond, Lancaster, New Hampshire. This species 

 is especially distinctive among North American Potamogetons . It 

 is not closely related to any other species and its pollen has a 

 unique surface pattern. It is usually found at greater depths 

 than most pondweeds, and then, sterile. Plants approaching the 

 surface often flower, but seldom set fruit. Only three 

 populations among those documented in New England herbaria were 

 represented by material with mature fruit. Leaves normally have 

 very minutely toothed margins (use strong lens) . P_^ robbinsii 

 forma cultellatus Fassett lacks toothed margins and is uncommon 

 in New England. Range extends from Labrador west to British 

 Columbia, south to New Jersey, Indiana, Alabama, Utah, and 

 California; most abundant in the northeast. 



alkalinity: mean, 26.1 mg/1; range 3.0-103.5 mg/1 

 pH: mean 7.2; range 6.3-8.9 



2. Potamogeton pectinatus L. Fig. 3, Map 3 



Locally abundant in scattered locations along the coast 

 and inland in calcareous lakes, rivers and shallow streams of 

 western New England, uncommon elsewhere. Although this species 

 is the major pondweed for duck food (Metcalf, 1931), its food 

 value in New England is low due to its limited occurrence. 

 Range extends throughout the United States and Canada. 



Rare and endangered plant list: New Hampshire 



alkalinity: mean 91.7 mg/1; range 27.5-231.5 mg/1 



pH: mean 8.0; range 6.5-10.7 



chloride: mean 408.2 mg/1; range 3.3-4095.0 mg/1 



3. Potamogeton f iliformis Pers. var. occidentalis (Robbins) 

 Morong Fig. 4, Map 4 



Known only from two locations in northern Aroostook 

 County, Maine. The nomenclature used follows Cronquist et al . 

 (1977). This robust variety is characterized by inflated 

 stipular sheaths in young plants which are similar to those of 

 P. vaginatus Turcz. These sheaths deteriorate early, hence are 

 lacking on older plants. This was previously reported as P. 

 vaginatus by Hellquist (1977) . Range extends from Nova Scotia 

 west through southern Canada, south to Maine, Michigan, Texas, 

 Colorado, New Mexico, and Arizona. 



alkalinity: mean 103.5 mg/1 

 pH: mean 7.3 



4. Potamogeton f iliformis Pers. var. alpinus (Blytt) Aschers. 

 and Graebner Fig. 5, Map 5 



Locally abundant in shallow calcareous waters and marl 

 springs of Aroostook County, Maine; uncommon at scattered 

 locations in northern New Hampshire and Vermont. This taxon is 



