OO EE _  _—————— 
PONDWEED FAMILY. 71 
14. Potamogeton praelongus Wulf. White-stemmed Pondweed. (Fig. 155.) 
Potamogeton praelongus 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, %4’-14’ wide, with 3-5 main nerves; 
stipules white, scarious, obtuse and commonly 
closely embracing the stem; peduncles 3/—20’ 
long, erect, straight, about as thick as the stem; 
spikes 1/-2’ long, thick, cylindric; fruit dark 
green, obliquely obovoid, 2’’-214’’ long, 1%4//- 
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. 
Nova Scotia to British Columbia, south to New Jer- 
sey, Minnesota and California. Also in Europe. 
Fruits in June and July, and usually withdraws its t WW) 
stems beneath the water as soon as the fruit is set, oe z 
15. Potamogeton perfoliatus L. Clasp- 
ing-leaved Pondweed. (Fig. 156. ) 
Potamogeton perfoliatus I. Sp. Pl. 126. 1753. 
Stems slender, much branched. Leaves all sub- 
merged, orbicular or ovate, sometimes lanceolate, 
usually obtuse and minutely serrulate at the apex, 
cordate-perfoliate at the base, 5’-15’ long, 3//-12/7 
wide; peduncles 114’ long, usually erect or slightly 
spreading; spikes 8/’-12’’ long, often flowering 
and fruiting under water; fruit obliquely obovoid, 
/114//-1%4’’ long, 1’’ thick, obscurely 3-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 streams, Newfoundland to British 
Columbia, south to Florida and California. Also in 
Europe and Asia. July—Sept. 
Potamogeton perfoliatus Richardsonii A. Bennett, Britten’s Journ. Bot. 27: 25. 1889. 
Potamogeton perfoliatus var. lanceolatus Robbins in A. Gray, Man. Ed. 5, 488. 1867. Not Blytt 1861- 
Leaves 1'-4%' long, 4/'-8'' wide at the broadened amplexicaul base, often curving inward 
at the apex, 13-23-nerved. Fruit somewhat larger than that of the type, about 2'’ long and 1%’ 
thick. Lake Champlain to Oregon, south to Delaware, Nebraska and California. 
16. Potamogeton Mysticus Morong. Mystic 
Pond Pondweed. (Fig. 157.) 
Poatamogeton Mysticus Morong, Coult. Bot. Gaz. 5:50, 1880. 
Whole plant very slender and delicate, stems irregu- 
larly branching above, nearly filiform, terete, 1°-4° long. 
Leaves all submerged, scattered, oblong-linear, 1/—1%4’ 
long, 1/’-3’’ wide, 5-7-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 1’~2’ long; immature fruit obovoid, less 
than 1’ long, about %’’ wide, obscurely 3-keeled on the 
back, slightly beaked by the slender, recurved style. 
Mystic Pond, Medford, and Miacount Pond, Nantucket, 
Mass. Aug-—Sept. 
