84 



ZANNICHELLIACEAE 



Leaves all submerged and similar. 

 Leaves lanceolate, oblong or ovate. 

 Leaves not clasping at base. 

 Leaves serrulate only at tip. 

 Leaves serrulate throughout. 

 Leaves clasping or half clasping at base. 



Stipules conspicuous and persistent; leaves half clasping. 

 Stipules short and inconspicuous. 

 Leaves narrowly linear or setaceous. 

 Stipules free from the leaves. 



Without propagating buds or glands. 

 With propagating buds or glands or both. 

 Stems filiform; leaves capillary. 

 Stems much flattened; leaves narrowly linear. 

 Stipules adnate to the leaf or petiole. 



Leaves narrowly linear, 1 mm. broad or more. 



Nutlets 1-keeled or without keel; leaves in terminal clusters. 

 Nutlets 3-keeled; leaves 2-ranked. 

 Leaves capillary, less than 1 mm. wide. 



10. P. lucens. 



11. P. crispus. 



12. P. praelongus. 



13. P. richardsonit. 



14. P. foliosns. 



15. P. piisillus. 



16. P. compressus. 



17. P. latifoUus. 



18. P. robbinsii. 



19. P. pectinatiis. 



1. Potamogeton natans L. 



Common Floating Pondweed. 



Fio-. 173. 



Potamogeton natans L. Sp. PL 126. 1753. 



Stems simple or sparingly branched, 6-15 dm. long. 

 Floating leaves 5-10 cm. long, 2.5-5 cm. wide, ovate, 

 oval or elliptic, rounded or subcordate at base, many- 

 nerved, thick, on petioles a little longer to three times 

 as long ; submerged leaves reduced to bladeless petioles, 

 commonly perishing and seldom seen at the fruiting 

 period; stipules usually over 5 cm. long, acute, 2-keeled; 

 peduncles 5-10 cm. long, as thick as the stem ; spikes 

 cylindric, about 5 cm. long, dense; fruit 4-5 mm. long, 

 narrowly obovoid, turgid, scarcely keeled ; style broad 

 and facial ; nutlet hard, more or less pitted or impressed 

 on the sides, 2-grooved on the back ; embryo forming 

 an incomplete circle, the apex pointing toward the base. 



British Columbia and Nova Scotia to New Jersey, Nebraska, 

 and southern California. Also in Europe and Asia. Transition 

 and Boreal Zones. Type locality: in Europe. 



2. Potamogeton diversifolius Raf. 

 Rafinesque's Pondweed. 



Fig. 174. 



Potamogeton hvbridus Michx. Fl. Bor. Am. 1: 101. 1803, 



not Thuill. " 1790. 

 Potamogeton diversifolius Raf. Med. Rep. IL 5: 354. 



1808. 



Stems flattened or sometimes terete, much- 

 branched. Floating leaves coriaceous, the largest 

 2-5 mm. long, 12 mm. wide, oval or elliptic and 

 obtuse, or lanceolate-oblong and acute ; petioles 

 shorter or sometimes longer than the blade, fili- 

 form or dilated ; submerged leaves setaceous, 

 seldom over 0.5 mm. wide, 2.5-8 cm. long; 

 stipules 6-10 cm. long, obtuse or truncate ; 

 emersed spikes cylindric, 6-10 mm. long, many- 

 flowered, on peduncles 6-14 mm. long, the sub- 

 merged globular, few-flowered, on peduncles 4-6 

 mm. long; fruit cochleate, rarely over 1 mm. 

 long, 3-keeled, the middle keel narrowly winged 

 and usually with 7-12 knob-like teeth on the 

 margin, the lateral keel sharp or toothed ; embryo 

 coiled lJ/2 times. 



In still water, Maine to Florida, and Cuba, west to Texas, northern 

 locality: Carolina. 



Mexico, and ("aliforn-.a. Type 



