10 Naiadaceae 



Flowers perfect. 



Perianth of 4 distinct segments. 1. POTAMOGETON. 



Perianth none. 2. RDPPIA. 



.Flowers monoecious or dioecious. 



Fresh-water plants ; flowers monoecious. 



Leaves entire. 3. ZANNICHELLIA. 



Leaves spiny-toothed on the margins. 4. NAIAS. 



Marine plants. 



Flowers monoecious ; carpels ovoid. 5. ZOSTERA. 



Flowers dioecious; carpels heart-shaped. 6. PHYLLOSPADIX . 



1. POTAMOGETON L. PONDWEED. 



Perennial herbs. Leaves alternate or the uppermost 

 often opposite, often of 2 kinds, submerged and float- 

 ing, the floating elliptic or ovate, the submerged linear. 

 Spikes sheathed by the stipules in the bud. Peduncles 

 axillary, bearing small perfect flowers. Perianth segments 

 4, herbaceous concave, valvate in the bud, short-clawed. 

 Stamens 4, inserted on the claws of the perianth segments ; 

 anthers sessile. Ovaries 4, sessile distinct 1-celled, 

 1-ovuled, attenuate into a short erect or recurved style. 



* With floating and submerged leaves. 



1. P. natans L. Stems 1-1.5 m. long, simple or sparingly 

 branched; floating leaves thick ovate-elliptic to lanceolate, 

 rounded or subcordate at base, 4-8 cm. long, mostly shorter than 

 the petiole; submerged leaves reduced to phyllodes or bladeless 

 petioles; peduncle as thick as the stem, 4-8 cm. long; spike 

 dense, 4 cm. long; fruit turgid, 4 mm. long, narrowly obovoid; 

 nutlet pitted on the sides, 2-grooved on the back. 



Bear Valley, San Bernardino Mountains. Not known within our limits. 



2. P. lonchites Tuckerm. Stems 1-2 m. long, much branched ; 

 floating leaves rather thin, elliptic, pointed at both ends, 5-10 

 cm. long; submerged leaves linear-lanceolate, 10-15 cm. long, 

 4-20 mm. wide, rounded at base or tapering into a petiole; stip- 

 ules 2-8 cm. long, free from the leaves; peduncles thickening 

 upward, 4-6 cm. long; spikes dense, 2-4 cm. long; fruit 4 mm. 

 long, obliquely obovoid, sides smooth, 3-keeled on the back. (P. 

 fluitans Roth. ?) 



Occasional in ponds in the valley region. 



