NAIADACE^. (POND-WEED FAMILY.) 833 



or cordate at base. Peduncles as thick as stems ; spike dense, cylindri- 

 cal, .03 to .05 long; sepals round-rhomtoid ; sides of the turgid nutlet 

 with a deep depression in the middle — June — Stagnant "water. 



* * All the leaves alihe, siilmerged and alternate (except those under the 

 peduncles lohich are nearly opposite), ovate or lanceolate. Stipules free. 



2. P. luceii§, L. 71 Stem branched. Leaves memlranous, pellu- 

 cid, short-petioled, cuneate at base, ovate to ovate-oblong and lanceo- 

 late, .OG to .1 long, .01 to .03 broad, serrate-roughened at margin. 

 Peduncles thicker than stems, thickened above. Spike dense, cylindri- 

 cal, .03 to .03 long; sepals transversely elliptical; nutlets obliquely 

 elliptical, somewhat flattened, when recent with obtuse, slightly keeled 

 margin — Summer — Lake of Yamuni. 



3. P. perfoliatus, L. If Stem branched. Leaves many-nerved, 

 membranous, pellucid, cordate-clasping at base, ovate to ovate-lanceo- 

 late, .03 to .00 long, with roughish margins. Peduncles as thick as 

 stems, longer than the short-cylindrical spike ; sepals slwrt-ovaie ; recent 

 nutlets obovate, compressed, with obtuse margin — Summer — Jordan. 



4. P. ciispu§, L. If Stem forked, somewhat flattened. Leaves 

 membranous, sessile, oblong to oblong-linear, .05 to .08 long, .005 to 

 .01 broad, serrulate, crisp-wavy at margin. Peduncle as thick as stem, 

 three to four times as long as somewhat interrupted spike; sepals ovate; 

 nutlets ovate, compressed, ending in a slender, recurved beak nearly as 

 long as they — Summer — Arabia Petrsea ; Hauran ; Damascus. 



Yar, PIiialen§is, Post. (Bull. Herb. Boiss., L 409.) Leaves 

 scarcely or not at all serrulate; spikes globular to oblong, 7-30-flowered 

 — Lake Phiala {Birl:et-er-Rdm). 



* ''' * All the leaves submerged, grass-lilce, alihe, and {with tlie exception of 

 those subtending the 2}^dtmcles, ichich are nearly opp>osite) alternate. 



Stipules free. 



5. P. Piiiala3 , Post. (Bull. Herb. Boiss., I. 409.) % Stem fili- 

 form, much branched; leaves membranous, pellucid, sessile, capillary, 

 3-nerved, short-mucronate, .03 to .03 long, .001 broad. Peduncles 

 longer than leaves; spike short, 3-4-flowered, interrupted; nutlets 

 scarcely compressed, oblique, rhomboid-orbicular, coarsely tubercled at 

 bacJc, mucronate at the base and apex of the inner margin — June — Lake 

 Ph ial a {Birlet-er-Rdm) . 



* *• * * ^^11 iJiQ leaves submerged, grass-like, alternate, the base produced 



into a sheath adnate to the stipule. 



6. P. pectinatiis, L. If Stem filiform, much branched. Leaves 

 setaceous, obsoletely grooved, acute, 1-nerved, transversely veined. 

 Peduncles elongated ; flowers in remote, somewhat one-sided clusters, 



forming long, slender, interrupted spikes ; sepals somewhat broader than 

 long; nutlets semilunar, somewhat compressed, with obtuse back, and 

 the inner margin straight, ending in a short beak — Summer — Birket- 

 Buswayeh (Lebanon). 



***** All the leaves submerged, and opposite, the lower icithout stipules, 

 the floral one or two with a stipule on one or both sides. 



7. P. clen§ii§, L. 2f Stems cylindrical, forked. Leaves decus- 

 sate, sessile, clasping^ membrano^is, pellucid, elliptical to ovate-lanceolate, 



