90 



ZANNICHELLIACEAE 



18. Potamogeton robbinsii Oakes. 

 Robbins' Pondweed. Fig. 190. 



Potamogeton robbinsii Oakes, Mag. Hort. Hovey 7: 



180. 1841. 



Stems slender, branched and sometimes 

 rooting at the nodes. Leaves all submerged, 

 crowded, linear, 8-13 cm. long, 2.5-4 mm. wide, 

 apiculate or acute at the apex, somewhat 

 clasping at base, minutely serrulate through- 

 out, many-nerved ; stipules adnate to the leaf-' 

 bases, the sheath 1-1.5 cm. long, the free por- 

 tion longer ; peduncles 3-10 cm. long, a little 

 more slender than the stem ; spike slender, 1-2 

 cm. long, many-flowered but sparingly fruit- 

 ing; nutlets slightly pitted, 3-keeled, the middle 

 keel more prominent than the lateral ; embryo 

 a complete spiral, the apex pointing toward 

 the base or inside it. 



In still water in the cool temperate region of 

 North America; New Brunswick, British Columbia, 

 and Pennsylvania to the Pacific Coast, where it is 

 sparingly distributed from British Columbia to Honey Lake, Lassen County, Cal 

 Transition Zones. Type locality: Pondicherry Pond, Jefferson, New Hampshire. 



ifornia, in the Boreal and 



19. Potamogeton pectinatus L. 



Fennel-leaved Pondweed. 



Fig. 



191. 



Potamogeton pectinatus L. Sp. PI. 126. 1753. 



Potamogeton colnmbianus Suksdorf, Deutsch. Bot. Monatss. 

 19: 92. 1901. 



Stems slender, 0.5-2 m. long, much branched, the 

 branches repeatedly dichotomous. Leaves very nar- 

 rowly linear or commonly setaceous, attenuate to the 

 apex, 1-nerved with a few transverse veins; stipules 

 adnate half their length, 15-25 mm. long, their sheaths 

 scarious on the margins ; peduncles filiform, 5-25 mm. 

 long ; the flowers in 2-6 verticels ; nutlets obliquely 

 obovoid, rounded on the back, 3-4 mm. long, with two 

 obscure keels ; embryo a complete or incomplete 

 spiral, the embryo pointing toward the base or in- 

 side it. 



\n still, fresh or brackish water, and cosmopolitan in its 

 distribution. On the Pacific Coast it is the most widely dis- 

 tributed and abundant species. Type locality: Europe. 



2. RUPPIA L. Sp. PI. 127. 1753. 



Stems capillary, widely branched. Leaves all submerged, very slender, attenuate, 1-nervef' 

 with membranous sheaths at the base. Flowers on a capillary spadix-like peduncle, naked, 

 perfect, consisting of 2 sessile anthers, 2-celled, attached by the back to the peduncle, having 

 between them several pistillate flowers with sessile peltate stigmas in 2 sets on opposite sides 

 of the rachis, the whole at first enclosed in the sheathing base of the leaf ; in development the 

 peduncle elongates, bearing the pistillate flowers at the end; fertilization takes place at the 

 surface, after which the peduncle coils up. Fruit a sinall obliquely pointed drupe, pediceled ; 

 embryo oval, curved. (Name in honor of Heinrich Bernhard Rupp, a German botanist.) 



A genus of three or four species, growing in salt and brackish water all over the world. Type species, 

 Riippia maritima \^. 



Sheaths of the stipules 10 mm. long or less, the free part shorter. 1. R. maritima. 



Sheaths of the stipules IS mm. long, the free part as long. 2. R. occidentalis. 



