25. Potamogeton Vaseyi Robbins. Vasey's Pondweed

Fig. 198

Potamogeton Vaseyi Robbins in A. Gray, Man. Ed. 5, 485. 1867. Potamogeton Vaseyi var. latifolius Morong, Mem. Torr.

Club, 3: Part 2, 44. 1893.

Stems filiform, widely branching below, and with many short lateral branches above, l°-l 1/2° long, the emersed fertile forms in shallow water, and the more common sterile submerged forms in water from 6°-8° in depth. Floating leaves on the fertile stems only, coriaceous, in 1-4 opposite pairs, oval oblong or obovate, 4"-5" long, 2"-3" wide, with 5-9 nerves deeply impressed beneath, tapering at the base into petioles 3'-4" long; submerged leaves capillary, i'-i 1/2' long; stipules white, delicate, many-nerved, acute or obtuse, 2"-3" long; peduncles 3"-6" long, thickening in fruit; spikes 2 '-3 ' Jong, 2-6-fruited; fruit round-ish-obovoid, about 1" long and nearly as thick, 3-keeled, the middle keel rounded, tipped with a straight or recurved style.

Quebec to Wisconsin, south to southern New York. The plant is furnished with propagating buds. July-Aug.

26. Potamogeton Lateralis Morong. Opposite-Leaved Pondweed

Fig. 199

Potamogeton lateralis Morong, Coult. Bot. Gaz. 5: 51. 1880.

Stems filiform, much branched. Floating leaves on sterile shoots only, coriaceous, elliptic, obtuse, 4"-5" long, 1"-2" wide, 5-7-nerved, the nerves deeply impressed beneath, usually in 1-3 opposite pairs which stand at right angles to the stem, on petioles 3"-10" long; submerged leaves linear, acute, 1'-3' long, 1/4"-1/2" wide, 1-3-nerved, 2-glan-dular at the base, but the glands small and often obsolete; stipules small, hyaline, many-nerved, obtuse, deciduous; peduncles and floating leaves lateral, with a peculiar appearance, widely spreading at maturity, sometimes recurved, thickening in fruit, 4"-15" long; spikes capitate or often interrupted, 3-4-flowered; fruit obliquely obovoid, about 1" long, lenticular, the back much curved and 2-grooved, the face arched and surmounted by the nearly sessile stigma; curve of the embryo Oval, its apex nearly touching its base.

In lakes and slow streams, Massachusetts and Connecticut. Proliferous shoots at the summit of the stem and on the upper branches appear late in the season, as the plants are beginning to decay. July-Aug. A rare and local plant, which, in an incompletely developed state, when it lacks the broad floating leaves, has the aspect of P. pusillus; its affinities are probably with P. Vaseyi and P. diversifolius.

27. Potamogeton Pusillus L. Small Pondweed

Fig. 200

Potamogeton pusillus L. Sp. PI. 127. 1753. Potamogeton panormitanus Biv. Sic. PI. 1806-7. Potamogeton pusillus polyphyllus Morong, Coult. Bot.

Gaz. 5: 51. 1880. Potamogeton pusillus sturrockii A. Bennett in Hook.

Stud. Fl. Ed.3, 435. 1884. Potamogeton pusillus panormitanus Morong, Mem.

Torr. Club, 3: Part 2, 46. 1893.

Stems filiform, branching, 6'-2° long. Leaves all ' submerged, linear, obtuse and mucronate or acute at the apex, 2-glandular at the base, 1'-3' long, about 2" wide, 1-3-nerved, the lateral nerves often obscure, or the leaf apparently nerveless; stipules short, hyaline, obtuse; peduncles usually 3"-9", or rarely 3' long; spikes 3-10-flowered; fruit obliquely ellipsoid, about 1" long and 1/2" thick curved and 2-grooved on the back or sometimes with 3 distinct keels, the face slightly arched, beaked by a straight or recurved style; apex of the embryo slightly incurved and pointing inside the base. Propagative buds occur in greater or less abundance.

In ponds and slow streams, New Brunswick to British Columbia, south to Virginia, Texas and California. Also in Europe. July-Aug. The forms listed in the above synonymy are all more or less distinctly, if inconstantly variable from the type. They are not sufficiently stable to merit specific recognition.

This is the commonest of the completely submerged Pondweeds. It may readily be distinguished from all other species of its group by its boat-shaped stipules which are usually twice as wide as the base of the leaf.