r NAIAD ACBAB (PONDWEED FAMILY) 35 



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

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



11. PotamogetonfoliosusRaf. Med. Rep. II. 5: 3.54. 1808. Stem filiform, 

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

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

 l-47flower^d, i on short club-shaped peduncles; fruit roundish-lenticular, the 

 ba,Qk,more or less crested. — ^Mostly in still water, often in stagnant and alkaline 

 ponds; Colorado to Montana, a,nd 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^ 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. Potaniogeton filifonnis 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 spadixj! which is at first inclosed in the shealthing 

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

 two sessile stamens, each with 2 large and separate anther-cells, and 4 small 

 ses^le ovaries. ^ Stigma sessile, depressed. , Fruit small obliquely .ovate, pointed 

 drupes, each raised" oni 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. K. maritima. 



Pedicels 3-6 cm.' long; fruit gibbous at base and strongly curved . . ' 2. R. curvitarpa. 



1. R'uppiia maritima L. Sp. PI. 127. 1753. Leaves linear-capiUary: 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.Tm 

 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. Nels: Bull. Torr. Bot. Club26: 122. 1899. Stems 

 light green, 6 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 3-3 cm. long: drupes black at maturity, oblong, 2 mm. 

 in length, gibbous at ba.se, Jience appearing obliquely placed oh the pedicel, 

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

 tipped with ^ sharp acumination. — 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 wiih' small stipules. Flowers monoecious, axillary; sessile , 

 or nearly so.' Sterile flowers of a single naked staimen 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. 



i. Za;amchellia palustris L. Sp. PI. 969. 1753. Stems 1-.5 dm. long or 

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

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



