NAJADACEAE. 27 



Potamogeton richardsonii (Benn.) Rydb. Leaves all submersed, lanceo- 

 late, acuminate, cordate and clasping at base, 6-10 cm. long; stipules large, 

 often split into shreds; peduncles rather short, thicker upward; spikes loose, 

 1-1.5 cm. long. 



Very common in lakes and ponds. 



Potamogeton zosterifolius Schumacher. Stems branching, flattened; 

 leaves grass-like, clasping at base, 3-nerved; stipules obtuse; spikes cylindric, 

 12-15-flowered, shorter than the peduncles. 



Quiet waters, rare. 



Potamogeton pusillus L. Stems very slender, flattened, usually much 

 branched; leaves all submersed, narrowly linear, 2-5 cm. long, each bearing 

 two glands at the sessile base; stipules obtuse, early disappearing; spikes in- 

 terrupted, 5-8-flowered. 



Common in still lakes. 



Potamogeton robbinsii Oakes. Stems stout; leaves numerous, all submer- 

 sed, linear or lanceolate, minutely serrulate, 8-12 cm. long, 2-ranked; stipules 

 obtuse; fruit obovoid, sharp beaked, conspicuously keeled. 



In quiet lakes, very local and seldom fruiting; abundant in Lake Cushman, 

 Mason County, Washington. 



Potamogeton pectinatus L. Stems filiform, branched, 30-90 cm. long; 

 leaves narrowly linear, attenuate to the apex, 1-nerved, 2-10 cm. long; ped- 

 uncles slender; flowers in whorls; fruit obliquely ovoid, compressed, turgid, 

 3.5-4.5 mm. long; style straight or nearly so. 



Columbia River, Scouler, Suksdorf; occurs most commonly in brackish 

 water but rare in our limits. 



36. RUPPIA. 



Slender submersed branching herbs growing in salt or brackish 

 water with thread-like stems and with thread-like alternate 

 leaves broadly sheathing at the base; flowers perfect, two or 

 more near each other on a spadix enclosed in the sheathing base 

 of a leaf, later being thrust out; perianth none; stamens 2, ses- 

 sile; ovaries 4, at first sessile, in fruit stalked. 



Ruppia maritima L. Stems slender, much branched, leafy; leaves narrowly 

 linear, 2-8 cm. long; spikes small, 2-8-flowered. 



In brackish shallow water on the seashore. A polymorphous species, of 

 which at least two subspecies occur in our limits. 



Ruppia maritima intermedia (Thed.) Aschers. & Graebn. Carpels ovoid, 

 slightly oblique but not curved, bluntly and inconspicuously beaked. 

 Seattle, Piper. 



Ruppia maritima rostrata Agarclh. Carpels strongly oblique or curved and 

 conspicuously beaked. 



Victoria, British Columbia, Macoun; Seattle, Piper & Smith. 



37. ZANNICHELLIA. 



Submersed herbs; leaves small, opposite, linear; flowers 

 unisexual, in axillary clusters, each composed of one staminate 

 and 2-5 pistillate flowers; staminate flower naked; pistillate 

 flowers enclosed in a funnel-shaped undivided involucre; style 

 short; stigma disk-shaped or bilobed; ovary flask-shaped. 



