SCHEUCHZERIACEAE (ARROW-GRASS FAMILY) 



2 a Floating leaves 30-50 nerved 



LARGE-LEAVED PONDWEED. (P. amplifblius.) 

 b Floating leaves less than 3o-nerved 3 



3 a Floating leaves 5-7 nerved 



RAFINESQUE'S PONDWEED. (P. diversifblium.) 

 b Floating leaves 9-29 nerved 4 



4 a Submerged leaves narrowly linear, about Vs in. broad, 



bladeless, or sometimes wanting 



COMMON FLOATING PONDWEED. (P. natans.) 

 h Submerged leaves usually lanceolate to linear, T /i in. 



or more broad 5 



5 a Submerged leaves 7-15 nerved; stipules pointed 



LONG-LEAVED PONDWEED. (P. lonchltes.) 

 b Submerged leaves 3-7 nerved; stipules blunt 6 



6 a Floating leaves ovate to lanceolate, 9-20 nerved; plant 



much branched 



VARIOUS-LEAVED PONDWEED. (P. heterophyllus.) 

 b Floating leaves elliptic to obovate, 11-27 nerved; plant 



rarely branched. .. . NUTTALL'S PONDWEED. (P. nuttdllii.) 



7 a Leaves rounded to lanceolate with clasping bases 



CLASPING-LEAVED PONDWEED. (P. perfoliatus.) 

 b Leaves grass-like or bristle-like 8 



8 a Submerged leaves 3-nerved 9 



b Submerged leaves i-nerved, bristle-like n 



9 a Spikes elongated, cylindric 



EEL-GRASS PONDWEED. (P. zosteraefblius.) 

 b Spikes rounded 10 



10 a Leaves with 2 translucent glands at the base, plainly 



3-nerved SMALL PONDWEED. (P. pusillum.) 



b Leaves without glands at the base, obscurely 3-nerved 



LEAFY PONDWEED. (P. foliosus.) 



11 a Branches repeatedly forked; flowers in remote whorls 



FENNEL-LEAVED PONDWEED. (P. pectinatus.) 

 b Branches not forked ; spikes rather cylindric 



RAFINESQUE'S PONDWEED. (P. diversifblius.) 



3 ZANNICHELLIA HORNED PONDWEED. (Z. palustris.) 



4 NAIAS SLENDER NAIAS. (N. flexilis.) 



5 ZOSTSRA EEL-GRASS. (Z. marina.) 



2 SCHEUCHZERIACEAE. Arrow-grass Family. 



t TRIGLOCHIN. 



i a Capsule linear; ovaries 3 



MARSH ARROW-GRASS. (T. palustris.) 

 b Capsule ovoid ; ovaries 6 



SEASIDE ARROW-GRASS. (T. marifima.) 



in 



