530 FLORA OF TEXAS. 



leaves ovate, cordate, clasping, obtuse, many-nerved, those 

 at the branches and peduncles opposite; spikes lateral and 

 terminal, oblong, densely many-flowered, on stout pedun- 

 cles 2-3 times as long as' the leaves; acJieniiim ohYKiiiely 

 obovate, rounded on the back, short-pointed. Fresh or 

 brackish water. July-September. Stems l°-2° long; 

 leaves 6"-8 ' long. 



P. LUCEKS, L. ? Steins sparingly branched ; leaves lan- 

 ceolate, acute, contracted and sessile at the base, pellucid, 

 5-9-nerved, wavy on the margins; stipules (white) con- 

 nate, rounded on the back ; spikes cylindrical, many-flow- 

 ered, on stout peduncles shorter than the leaves ; achenium 

 (immature) oval, compressed, rounded on the back, short- 

 pointed. Freshwater. August. Stems 2°-3° long; leaves 

 2-3' long, equaling the spikes. 



** Leaves of two forms ; the immersed ones thin and pellucid, the floating ones long- 

 petioled and somewhat coriaceous. 



P. FLUITAXS, Eoth. Stem simple ; leaves many-nerved, 

 the floating ones varying from oblong-lanceolate to ovate, 

 acute at each end, or obtuse or cordate at the base, the 

 others large, oblong, gradually or abruptly short-petioled, 

 undulate; stipules connate and keeled on the back; joe- 

 duncles stout, thickened upward; spikes long, cylindrical, 

 dense-flowered; achenium smootli, 1-3-keeled on the back. 

 Fresh-water ponds and streams. June-August. Leaves 

 2-9' long. 



P. XATAXS, L., probably occurs within our limits, but I 

 have not seen specimens. It may be known by longer- 

 petioled (4-12') leaves, more ^l^n^QY peduncles, and round- 

 ed stijmles and achenia. 



P. HETEROPHYLLUS, Schreber. Stem slender, branching ; 

 floating leaves small, thin, elliptical or oblong-linear, on 

 filiform petioles; immersed leaves long, sessile, linear or 

 lanceolate ; stijmles connate, 2-ribbed ; peduncles thickened 

 upward; spikes narrowly cylindrical; achenium smooth. 



