This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Potamogeton mysticus Morong, Coult. Bot. Gaz. 5: 50. 1880.
Whole plant very slender and delicate, stems irregularly branching above, nearly filiform, terete, 1°-4° long. Leaves all submerged, scattered, oblong-linear, l'-l 1/2' long, 1"-3" wide, 5-7-nerved, obtuse and rarely with minute serrula-tions 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 1/2" wide, obscurely 3-keeled on the back, slightly beaked by the slender, recurved style.
Mystic Pond, Medford, and Miacount Pond, Nantucket, Mass. Aug.-Sept. Apparently a depauperate form of the preceding, and scarcely distinct from it. Perhaps a hybrid.
Potamogeton confervoides Reichb. Ic. Fl. Germ. & Helv. 7:
Stems slender, terete, much branched, the upper branches repeatedly forking, 6'-18' long. Leaves very delicate, flat, setaceous, l'- 2 1/2' long, the broadest scarcely \" wide, tapering to a long hair-like point, 1-3-nerved and often with a few cross-veins, bright green or yellowish; stipules delicate, obtuse, 2'-3" long; peduncles 2'-8' long, erect, somewhat thickened upward; spikes capitate, 3"-4" long; fruit roundish-obovoid, 1"-1 1/2" long and about as thick, the back sometimes a little angular or sinuate, 3-keeled, the middle keel sharp, the face notched near the base, the sides impressed with a shallow indentation which runs into the notch of the face; apex of the embryo nearly touching the base a little to one side.
In cold or mountain ponds, Maine and New Hampshire to New Jersey and Pennsylvania. Aug.-Sept.
Potamogeton crispus L. Sp. PI. 126. 1753. .
Stems branching, compressed. Leaves 2-ranked, linear-oblong or linear-oblanceolate, sessile or semi-amplexicaul, obtuse at the apex, serrulate, crisped, ¥-4' long, 3"-7" wide, 3-7-nerved, the midrib often compound and the outer nerves very near the margin; stipules small, scarious, obtuse, early perishing; peduncles 1'-2' long, frequently recurved in fruit, sometimes very numerous; spikes about ¥ long, appearing very bristly with the long-beaked drupelets when in fruit; fruit ovoid, about 1 1/2" long, 1" or more wide, 3-keeled on the back, the middle keel with a small projecting tooth near the base, the face slightly curved, the style facial and nearly as long as the drupelet; embryo small, its apex pointing directly toward its base. The plant is mainly propagated by peculiar winter buds.
In fresh or salt water, about cities, Massachusetts to Pennsylvania and Virginia. Also in Europe. Aug.