ZANNICHELLIACEAE 



79 



2. Ruppia L.* 

 I. R. maritima L. Atlantic and Pacific coasts of North America, 

 and in saline pools in the interior. 



Throughout the range along the coasts, and up the brackish 

 rivers within the influence of the tides. No definite records from 

 Pa., but probably along the Delaware River below Philadelphia. 



3. Potamogeton [Tourn.] L.* 



A. With floating and submerged leaves. (Floating leaves rarely 

 wanting in Nos. 9, 10 and 11.) 

 Mature submerged leaves linear or linear-lanceolate, 

 never more than 4 mm. wide, sometimes mere 

 phylloidia. 

 The straight apex of the embryo pointing towards 

 the base or outside it. 

 Submerged leaves reduced to phylloidia; 

 floating leaf-blades more than 3 cm. long. 

 Nutlets pitted; peduncles as thick as the 



petioles. 

 Nutlets smooth; peduncles twice as thick 

 as the petioles. 

 Submerged leaves with a proper blade; floating 

 leaves less than 1.2 cm. long. 

 The curved apex of the embryo pointing 

 inside the base. 

 Embryo coiled once, the apex point- 

 ing downward. 

 Embryo coiled 1 J 2 times; the apex 

 transverse or pointing upward. 

 Floating leaf-blades less than 2.5 

 cm. long; submerged leaves 

 without cellular reticula- 

 tion along the midrib. 

 Submerged peduncles 4-6.5 

 mm. long; submerged 

 leaves 0.4-0.9 mm. wide. 

 Submerged peduncles 0.3- 

 1.5 mm. long; submerged 

 leaves 1-1.4 mm. wide. 

 Floating leaf-blades more than 2.4 

 cm. long; submerged leaf with 

 cellular reticulation along the 

 midrib. 

 Mature submerged leaves lanceolate, ovate or elliptic, 

 never linear or more than 4 mm. wide except in 

 forms of P. heterophyllus. 

 Floating leaves 32-many nerved. 



* See footnote, page 76. 



1. P. natans. 



2. P. Oakesianus. 



3. P. lateralis. 



4. P. Vaseyi. 



5. P. diver sif alius. 



6. P. dimorphus. 



7. P. epihydrus. 



8. P. amplifolius. 



