46 Karl M. Wiegand and Arthur J. Eames 



4. S. minimum Fries. 



Muddy shores of ponds and ditches, mostly in neutral soils; rare. June 15-July. 



E. side of Summit Marsh (AT. M. W. & F. P. Mctcalf) ; swale s. side of Slater- 

 ville Swamp ; s. side of Chicago Bog. 



Newf. to Alaska, southw. to n. N. J., Pa., Term., Colo., and Oreg. ; infrequent 

 near the coast. Found also in Eurasia. 



14. NAJADACEAE (Pondweed Family) 



a. Flowers perfect, borne in spikes; anthers 2-4; leaves alternate, or the uppermost 

 ones sometimes opposite. 

 b. Stamens 4; connectives sepaloid ; carpels sessile in fruit. 1. Potamogeton 



b. Stamens 2 ; connectives not enlarged ; carpels stipitate in fruit. 



2. Ruppia 

 </. Flowers unisexual, axillary; anther 1 (2) ; leaves opposite or in 3's. 



b. Pistils 2-6, unsymmetrical in fruit, and undulate or toothed on one side ; leaves 

 entire, not dilated at base. 3. Zannichellia 



/'. Pistil 1, fusiform, regular, not toothed; leaves serrulate, dilated at base. 



4. Najas 



1. Potamogeton (Tourn.) L. 

 a. Ligules distinct from the petiole or leaf base (except sometimes in no. 12) ; 

 floating leaves often present. (2d a, p. 48.) 

 b. Submerged leaves lacking or reduced to the petiole only. 



c. Blade of floating leaves ovate-oval, subcordate ; fruit scarcely keeled, with 



a lateral depression in the nutlet. 1. P. natans 



c. Blade of floating leaves elliptical, tapering at base ; fruit 3-keeled especially 

 when dry, the keels undulate or crenate ; lateral depression in the nutlet 

 not present. 3. P. americanus, 



var. novacboraccnsis 

 b. Submerged leaves present, thin and delicate. 

 c. Submerged leaves broader than linear. 

 d. Base of submerged leaves tapering. 



e. Submerged leaves 2.5-8 cm. wide, 30-40-nerved, recurved ; floating leaves 

 30-55-nerved; fruit large, 4-5.5 mm. long, 3-keeled. 



2. P. amplifolius 

 e. Submerged leaves 3 cm. wide or less, 3-18-nerved; floating leaves, if 

 present, fewer-nerved than in no. 2. 

 /. Submerged leaves elliptic-lanceolate or elliptical, tapering toward each 

 end, very acute or mucronate, not suffused with red ; floating leaves, 

 when present, elliptical ; 1-2 carpels of each flower developing. 

 g. Floating leaves usually present ; fruit more or less 3-keeled. 



h. Floating leaves small, blade 1.5-6 cm. long ; submerged leaves 2-3 

 (6) cm. long, sessile; fruiting spikes 1-3 cm. long; fruit 2.5 mm. 

 long, scarcely keeled ; floating leaves usually obtuse, not really 

 apiculate. 4. P. gramincus, 



var. graminifolius 



h. Floating leaves larger, blade 5-12 cm. long ; submerged leaves 



6-30 cm. long ; fruiting spikes 2.5-7 cm. long ; fruit 3-4 mm. 



long, 3-keeled at least when dry. 



i. Upper submerged leaves on petioles 8-15 cm. long, frequently 



wanting ; floating leaves mostly obtuse, sometimes acute, not 



really apiculate. 3. P. americanus, 



var. novaeboracensis 

 i. Upper submerged leaves on petioles 1-4 cm. long, usually present ; 

 floating and submerged leaves acutish and apiculate. 



5. P. angustifolius 



