13. Potamogeton Lucens L. Shining Pondweed. Cornstalk-Weed

Fig. 186

Potamogeton lucens L. Sp. PI. 126. 1753.

Stems thick, branching below and often with masses of short leafy branches at the summit. Leaves all submerged, elliptic, lanceolate or the uppermost oval, shining, acute or acuminate and cuspidate, or rounded at both ends and merely mucronulate, sessile or short-petioled, 2 1/2'-8' long, 8"-2o" wide, the tips often serrulate; stipules 1'-3' long, 2-carinate, sometimes very broad; peduncles 3'-6' long; spikes 2'-2 1/2' long, cylindric, very thick; fruit about 1 1/2" long and 1 1/4" thick, roundish, the face usually with a slight inward curve at the base; apex of the embryo pointing transversely inward.

In ponds, Nova Scotia to Florida, west to California and Mexico. Local. Also in Europe. Sept.-Oct.

So ZANNICHELLIACEAE. Vol. I.

14. Potamogeton Praelongus Wulf. White-Stemmed Pondweed

Fig. 187

Potamogeton praelongus Wulf. in Roem. Arch. 3: 331. 1805.

Stems white, fiexuous, flattened, much branched, growing in deep water, sometimes 8° long. Leaves all submerged, oblong or oblong-lanceolate, semi-amplexicaul, bright green, 2'-12' long, 1/2'-1 1/4' 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"-2 1/2" long, 1 1/2"-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 Jersey, 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 L. Clasping-Leaved Pondweed

Fig. 188

Potamogeton perfoliatus L. Sp. PI. 126. 1753. Potamogeton perfoliatus lanceolatus Robbins in A. Gray,

Man. Ed. 5, 488. 1867. Not Blytt 1861. Potamogeton perfoliatus Richardsonii A. Bennett, Journ.

Bot. 27: 25. 1889. Potamogeton Richardsonii Rydb. Bull. Torrey Club 32:

599. 1905. Potamogeton bupleuroides Fernald, Rhodora 10: 46. 1908.

Stems slender, much branched. Leaves all submerged, orbicular or ovate, sometimes lanceolate, obtuse or acutish and minutely serrulate at the apex, cordate-perfoliate at the base, 5"-20" long, 3"-12" wide; peduncles1 1/4' long, usually erect or slightly spreading; spikes 8"-12" long, often flowering and fruiting under water; fruit obliquely obovoid, 1 1/4"-2" long, \\" thick, obscurely 3-carinate on the back, the face slightly curved outwardly toward the top, the sides with a shallow indentation which runs into the face; style nearly facial; embryo 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.