POXDWEED FAMILY 



89 



15, Potamogeton pusillus L. 

 Small Pondweed. Fig. 187. 



Potamogeton pusillus L. Sp. PI. 127. 1753. 



Stems filiform, branching, 3-6 dm. long. Leaves 

 all submerged, narrowly linear. 2-6 cm. long, 

 0.5-1.5 mm. wide, 1-3-nerved, the lateral nerves 

 often obscure, acute or subacute, furnished with 

 translucent glands on each side at tlie base ; winter 

 propagating buds occasional ; stipules short, hya- 

 line, free from the leaves, soon deciduous ; spikes 

 interrupted or capitate, 3-10-flowered ; peduncles 

 0.5-3 cm. long ; as thick as the stem or thinner, 

 erect or recurved ; nutlets smooth or ultimately 

 pitted, distinctly 3-keeled, 1.5-2 mm. long; apex of 

 the embryo incurved and pointing inside of the 

 base. 



In ponds and slow running streams, throughout the 

 northern hemisphere. Common on the Pacific Coast from 

 British Columbia to southern California, in both the Boreal 

 and Austral Zones. Type locality: Europe. 



16. Potamogeton compressus L. 

 Eel-grass Pondweed. Fig. 188. 



Potamogeton compressus L. Sp. PI. 127. 1753. 



Potamogeton sosteraefolius Schum. Enum. PI. Saell. 50. 1801. 



Stems much flattened, sometimes winged, widely 

 branching, often developing propagating buds. Leaves 

 all submerged, linear, 5-20 cm. long, 4-8 mm. wide, 

 grass-like, abruptly pointed, with 3 principal and many 

 fine nerves ; stipules scarious, oblong, very obtuse, soon 

 deciduous, free from the leaves ; peduncles 4-10 cm. 

 long, as thick as the stems ; spikes cylindric, many- 

 flowered, 15-20 mm. long, often interrupted; nutlets 

 smooth, 3-keeled, the lateral keels smaller than the 

 toothed or undulate middle one; embryo a complete 

 spiral, the curved apex pointing inside the base. 



Widely distributed over the cool temperate regions of the 

 northern hemisphere, mainly in the Boreal Zones; on the Pacific 

 Coast it ranges from British Columbia south to Honey Lake, 

 Lassen County, California, but it is not common and has been 

 collected in only a few localities. Type locality: Europe. 



17. Potamogeton latifolius (Robb.) 



jMorong. 

 Nevada Pondweed. 



Fig. 189;. 



Potamogeton latifolius Morong, Mem. Torrey Club. 3: 52. 



1893. 

 Potamogeton pcctinatus latifolius Robb. in S. Wats. Bot. 



King Expl. 338. 1871. 



Stem whitish, branched. Leaves all submerged, 

 linear, 2-8.5 cm. long, 1-1.5 mm. wide, acute or 

 obtuse at the apex ; primary nerves 3-5 with nu- 

 merous reticulated cross nerves ; stipules adnate 

 to the leaf-bases, scarious, the sheath 1-2.5 cm. 

 long, the free part shorter ; spikes cylindric, 2-3 

 cm. long, interrupted below ; peduncles whitish, 

 thinner than the stems, 2.5-8 cm. long ; nutlets 

 smooth, mostly without keels, rarelj^ with one in- 

 conspicuous keel ; embryo a complete spiral, the 

 curved apex pointing inside the base. 



A local species, restricted to northwestern Xevada and 

 northeastern California, in Modoc and Lassen Counties. 

 Transition and L'liper Sonoran Zones. Type locality: 

 Humboldt River, below Humboldt Lake, Nevada. 



