PONDWEED FAMILY 25 



long; peduncles 4-7 cm. long; spike interrupted, with 2-12 flowers in each whorl; 

 fruit ovoid, 2-3 mm. long, nearly 2 mm. thick, not keeled; stigma sessile. Ponds 

 and lakes: Que N.Y. Mich. Wyo. Alta. Je-Au. 



18. P. interior Rydb. Stem slender, branched, 3-6 dm. long; leaves linear, 

 3-15 cm. long, about 1 mm. wide, obtuse, with a strong midrib and raised or 

 re volute margins; peduncles 3-7 cm. long; spike interrupted; fruit obliquely 

 ovoid, 2-grooved on the back; stigma subsessile; free portion of the stipules 2-4 

 mm. long. P. marinus occidentalis Robbins. Ponds and lakes, especially in 

 alkali water: Ont. N.M. Utah Nev. Plain Submont. Jl-Au. 



19. P. pectinatus L. Stem slender, much branched, very leafy, 3-10 dm. 

 long; leaves setaceous, attenuate at the apex, 3-15 cm. long, 0.1-0.5 mm. wide, 

 sometimes nerveless; stipular sheath 1-2 cm. long; free portion 3-8 mm. long; 

 peduncles filiform, 5-20 cm. long; spike interrupted, with several whorls of flow- 

 ers; fruit obliquely ovoid, 3-4 mm. long. Fresh, salt, or alkali waters: N.B. 

 Fla. L. Calif. Alaska; Eu. Plain Submont. Jl-S. 



20. P. Robbinsii Oakes. Stem stout, widely branching, sometimes rooting 

 at the nodes, 5-10 dm. long; leaves linear, acute, crowded in 2 ranks, 7-12 cm. 

 long, 2-6 mm. wide, auricled at the point of union with the stipules; stipular 

 sheath about 1 cm. long; free portion of the stipules 1-2 cm. long, mostly lacerate; 

 peduncles 3-10 cm. long; spike interrupted, flowering under water; fruit obovoid, 

 about 4 mm. long, 3 mm. thick, 3-keeled, the middle keel sharp. Ponds and 

 lakes: N.B.N.J Mich. Ida. Ore. B.C. Plain. Jl-S. 



2. RUPPIA L. 



Slender water plants, widely branched and with capillary stems, filiform 

 alternate 1-nerved leaves, with membranous sheaths. Peduncles spadix-like, 

 filiform, at first very short, at last generally much elongated and spirally coiled. 

 Flowers consisting of 2 sessile anthers, and 4 pistils, sessile at first, in fruit long- 

 stipitate. Fruit small, more or less obliquely ovoid drupes. 



Sheaths 610 mm. long; drupe about 2 mm. long or less. 



Drupe very oblique; beak 0.5-1 mm. long. 1. R. maritima. 



Drupe scarcely oblique, almost beakless. 2. R. pectinata. 



Sheaths 20-40 mm. long; drupe 3-4 mm. long. 3. R. occidentalis. 



1. R. maritima L. Stem slender, filiform, whitish; leaves 2-10 cm. long, 

 0.5 mm. or less wide; sheaths 6-8 mm. long, with a short free tip; peduncles in 

 fruit sometimes 3 dm. long; drupes about 2 mm. long; beak almost straight or 

 curved. R. curvicarpa A. Nels. In brackish or salt water, along the coasts: 

 Newf. Tex. Alaska L. Calif.; occasionally in the interior, Sask. Mex.; Eur- 

 asia and S. Am. Plain Je-Au. 



2. R. pectinata Rydb. Stem intricately branched and very leafy, with 

 very short internodes; leaves filiform, 3-6 cm. long, 0.5 mm. or less wide; sheaths 

 7-10 mm. long, seldom with a small rounded tip; peduncles 3-5 cm. long, in 

 fruit recurved, but apparently not in a spiral; drupe about 1.2 mm. long, with 

 an almost sessile stigma. In brackish ponds : Yellowstone National Park, Wyo. 

 Utah Wash. Calif. Submont. Mont. 



3. R. occidentalis S. Wats. Stem comparatively stout, 3-6 dm. long, with 

 very short internodes and fan-like clustered branches; leaves 7-20 cm. long, and 

 0.3 mm. wide or less; sheaths with distinct free tips, often overlapping each 

 other; peduncles sometimes 5 dm. long; stipes about 25 mm. long; drupes ovoid 

 or pyriform, scarcely oblique; beak short, straight. In saline ponds: Neb. 

 B.C. Alaska. Plain Submont. Jl-Au. 



3. ZANNICHELLIA (Mich.) L. 



Slender branching aquatics, with opposite filiform leaves and sheathing mem- 

 branous stipules. Flowers monoecious, sessile, naked, usually both kinds in the 

 same axil; the staminate ones consisting of a single 2-celled anther, borne on a 

 pedicel-like filament, the pistillate ones of 2-6 sessile pistils in a cup-shaped in- 

 volucre. Fruit nut-like, obliquely oblong, flattened, with a short slender beak, 

 T ibbed or toothed on the back. Seed orthotropous. 



