NAIADACEAE (PONDWEED FAMILY) 35 



keeled: apex of embryo incurved and directed obliquely downward. In ponds 

 and slow streams; almost throughout North America, but rare in our range. 



11. Potamogeton foliosus Raf. Med. Rep. II. 5: 354. 1808. Stem filiform, 

 somewhat flattened, freely branching: leaves narrowly linear, 3-5 cm. long, 

 1-2 mm. broad, acute, obscurely 3-nerved; stipules obtuse: spikes capitate, 

 1-4-flowered, on short club-shaped peduncles: fruit roundish-lenticular, the 

 back more or less crested. Mostly in still water, often in stagnant and alkaline 

 ponds; Colorado to Montana, and across the continent. 



12. Potamogeton pectinatus L. Sp. PI. 127. 1753. The slender stems freely 

 branched, 3-8 dm. long; the branches repeatedly dichotomous: leaves tapering 

 to the setaceous apex, 1-nerved, 5-15 cm. long, sometimes capillary and nerve- 

 less; sheaths of the stipules with scarious margins: fruit obliquely ovoid, with 

 a hard thick shell, 3-4 mm. long, not keeled but with obscure lateral ridges on 

 the back, the sides full and convex. In fresh or saline waters; very common 

 in our range; across the continent. 



13. Potamogeton filiformis Pers. Syn. 1: 152. 1805. Resembling narrow- 

 leaved forms of the last species, low and very leafy: peduncles much elongated: 

 fruit much smaller (2 mm. long) and thinner, round-obovate, not keeled upon 

 the rounded back, tipped with the broad sessile stigma. P. marinus. Similar 

 habitat and about the same range as the last. 



2. RUPPIA L. 



Aquatic herbs, growing under water, with long and thread-like forking 

 stems, and slender almost capillary alternate leaves, sheathing at the base. 

 Flowers rising to the surface at the time for expansion, perfect, 2 or more ap- 

 proximated on a slender spadix, which is at first inclosed in the sheathing 

 spathe-like base of a leaf, entirely destitute of floral envelopes, consisting of 

 two sessile stamens, each with 2 large and separate anther-cells, and I small 

 sessile ovaries. Stigma sessile, depressed. Fruit small obliquely ovate, pointed 

 drupes, each raised on a slender stalk which appears after flowering; the 

 spadix itself also then raised on an elongated thread-form peduncle. 



Pedicels 1-3 cm. long; fruit conical-ovoid . . . . . 1. II. maritima. 



Pedicels 3-G cm. long; fruit gibbous at base and strongly curved . . 2. R. curvicarpa. 



1. Ruppia maritima L. Sp. PI. 127. 1753. Leaves linear-capillary: fruiting 

 peduncles capillary, 7-15 cm. long; pedicels 1-3 cm. long: fruit (drupe or nut) 

 conical-ovate, sometimes somewhat gibbous at base and obliquely erect. 

 Shallow bays and in marshes along the Atlantic and Pacific coasts; apparently 

 aiso in salt springs and creeks in the interior. 



2. Ruppia curvicarpa A. Xels. Bull. Torr. Bot. Club 26: 122. ls<)<). Stems 

 light green, G dm. or more in length, capillary and fragile at maturity: leaves 

 variable in length, 3 cm. or more: peduncles long: pedicels several in a cluster, 

 capillary, fragile, from 3-G cm. long: drupes black at maturity, oblong, 2 mm. 

 in length, gibbous at base, hence appearing obliquely placed on the pedicel, 

 increasing slightly in diameter upward to the abruptly bent beak which is 

 tipped with a sharp acurnination. Alkali lakes, southern Wyoming; probably 

 in similar waters elsewhere in the interior table-lands. 



3. ZANNICHELLIA L. 



Very slender and branching, with very narrow or filiform opposite leaves, 

 not sheathing and with small stipules. Flowers monoecious, axillary, sessile 

 or nearly so. Sterile flowers of a single naked stamen with slender filament. 

 Fertile flowers solitary, usually in the same axils, with a cup-shaped mem- 

 branous spathe or perianth; ovaries nearly sessile, becoming more or less stip- 

 itate; stigmas peltate. Fruit an obliquely oblong beaked nutlet. 



1. Zannichellia palustris L. Sp. PL 969. 1753. Stems 1-5 dm. long or 

 more, leafy: leaves 1-7 cm. long: fruit somewhat incurved, often more or less 

 toothed on the back. In fresh- water ponds and slow streams; from New 



