PONDWEED FAMILY. 

 14. Potamogeton praelongus Wulf. White-stemmed P.mdwecd. ! 



1'i'lanuiffflnn praelongns Wulf. in Roem. Arch. 3: 

 331. 1805. 



Stems white, flexuous, flattened, much 

 branched, growing in deep water, sometimes 8 

 long. Leaves all submerged, oblong or oblong- 

 lanceolate, semi-amplexicaul, bright green, 2'- 

 12' long, yi'-i%' wide, with 3-5 main nerves; 

 stipules white, scarious, obtuse and commonly 

 closely embracing the stem ; peduncles 3 / -2o / 

 long, erect, straight, about as thick as the stem; 

 spikes i'-2 / long, thick, cylindric ; fruit dark 

 green, obliquely obovoid, 2 // -2^ // long, ij^"- 

 2" thick, the back much rounded, often with the 

 upper curve nearly as high as the style ; the 

 middle keel sharp ; style short, obtuse, facial. 



X' iva Scotia to British Columbia, south to New Jer- 

 sey. Minnesota and California. Also in Europe. 

 Fruits in June and July, and usually withdraws its 

 stems beneath the water as soon as the fruit is set. 



15. Potamogeton perfoliatus I,. Clasp- 

 ing-leaved Pondweed. i Fig. ; 

 Potamogeto* perfoliatm* I.. Sp I'l i^. 1733. 



Stems slender, much branched. leaves all cub- 

 merged, orbicular or ovate, sometimes lanceolate. 

 usually obtuse and minutely serrulate at the apex, 

 cordate-perfoliate at the base, 5'-i5' long, 3" 

 wide; peduncles \}+' long, usually erect or slightly 

 spreading ; spikes 8"-i2" long, often flowering 

 and fruiting under water ; fruit obliquely obovoid, 

 i '4 "-i)4" long, i" thick, obscurely .v-carinate on 

 the back, the face slightly curved outwardly to- 

 ward the top. the sides with a shallow indentation 

 which runs into the face; style nearly facial; em- 

 bryo slightly incurved or with its apex pointing 

 directly toward the base. 



In ponds and *tn-am-. Ni fnutulland lo BritUh 

 Columbia, south to Florida and California. AUo in 

 Europe and Asia. July -Svpt 

 Potamogeton perfoliatus Richardsonii A. Bennett. Britten's Jour: l| -<>. l88>. 



Polanio^t'ton f>t'rfoliaius\-a.r. lanceolatns Robbins in A. Gray. Man. IM 



Leaves \' -\%' long, 4"-8" wide at the broadened amplexicaul base. -i mward 



at the apex, i3-23-nerved. Fruit somewhat larger than that of tin- t\ long and \\ 



thick. Lake Champlain to Oregon, south to Delaware, Nebraska and i 



16. Potamogeton Mysticus Morong. Mystic 



Pond Pondweed. (Fig. 157.) 

 P>tai'\ycton .'\frsiu-its Morong, Coult. Bot. Gaz. 5: 50. 



Whole plant very slender and delicate, stems irregu- 

 larly branching above, nearly filiform, terete, i-4 long. 

 Leaves all submerged, scattered, oblong-linear, \ f -\%,' 

 long, \"-$" wide, 5-y-nerved, obtuse and rarely with 

 minute serrulations near the apex, abruptly narrowed at 

 the base and sessile or partly clasping; stipules obtuse, 

 about 6" long, hyaline and with many fine nerves, mostly 

 deciduous, but sometimes persistent and closely sheathing 

 the stem; spikes few, capitate, 4-6-flowered, borne on 

 erect peduncles i / -2 / long; immature fruit obovoid, less 

 than i" long, about W wide, obscurely 3-keeled on the 

 back, slightly beaked by the slender, recurved style. 



Mystic Pond, Medford, and Miacount Pond, Nantucket, 

 Mass. Aug-Sept. 



