8 4 



ZANNICHELLIACEAE. 



VOL. I. 



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, i "-2" wide, s-7-nerved, the nerves 

 deeply impressed beneath, usually in 1-3 opposite 

 pairs which stand at right angles to the stem, 

 on petioles 3"-io" long; submerged leaves linear, 

 acute, i '-3' long, \"-\" wide, i-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."-! 5" long; spikes capitate 

 or often interrupted, 3-4-flowered ; fruit obliquely 

 obovoid, about i" 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 sum- 

 mit 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. diversifolins. 



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. 



Torn 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, i'-3' 

 long, about \" wide, i-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-io-flowered ; 

 fruit obliquely ellipsoid, about i" long and \" 

 thick curved and 2-grooved on the back or some- 

 times with 3 distinct keels, the face slightly 

 arched, beaked by a straight or recurved style ; 

 apex of the embryo slightly incurved and point- 

 ing 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 Cali- 

 fornia. Also in Europe. July-Aug. The forms listed 

 in the above synonymy are all more or less dis- 

 tinctly, 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 distin- 

 guished from all other species of its group by its boat-shaped stipules which are usually twice as 

 wide as the base of the leaf. 



