above the basal end or between the base and the middle of the opposite side. 



In neutral to acid water of ponds and rivers in Okla. (Waterfall), n.e. Tex. 

 (Bowie Co.), N. M. (Rio Arriba Co.) and Ariz. (Coconino Co.), May-Oct.; 

 throughout much of N. A. 



9. Pofamogeton diversifolius Raf. var. diversifolius. Fig. 39. 



Rhizome freely branching, rooting at the nodes; stem filiform, terete, much- 

 branched; stele of the oblong-type with one or two median bundles; endodermis of 

 0-cells; interlacunar bundles absent; subepidermal bundles absent or occasionally 

 with faint mechanical strands; pseudohypodermis present or absent; submersed 

 leaves narrowly linear, entire, pale-green, mostly 2-6 cm. long, 0.5-1.5 mm. wide, 

 slightly tapering to a sessile base, acute to obtuse at apex; nerves 3, laterals in- 

 conspicuous; midrib usually bordered by 1 to 4 rows of lacunae; stipules delicately 

 fibrous, adnate to the base of the leaf blade; floating leaves coriaceous, elliptic to 

 oval or narrowly obovate, rounded at apex, cuneate or rounded at base; petioles 

 usually shorter than the blades; blades to 4 cm. long and 2 cm. wide; nerves 5 

 to 15; stipules free from the petioles, 6-30 mm. long, delicately fibrous, persistent; 

 peduncles usually slender, often clavate, 1-^ mm. long from the axils of submersed 

 leaves and 2—30 mm. long from the axils of floating leaves, ascending or arching; 

 submersed spikes few-flowered, subglobose; emersed spikes elongate, 5-20 mm. 

 long, in fruit 3-4 mm. wide; flowers sessile or nearly so; perianth suborbicular to 

 broadly rhombic, 0.7-1 mm. long, with a short claw; fruits suborbicular, the sides 

 flattened or slightly concave and often cochleate-sulcate, 1—1.5 mm. in diameter; 

 dorsal keel prominent, alate, 0.2-0.4 mm. wide, undulate or with a few very low 

 teeth; lateral keels low and fine but evident, entire or slightly dentate; beak facial, 

 minute but usually definite; exocarp greenish to brownish, endocarp with loop 

 solid; embryo coil more than one complete revolution; winter-buds may form 

 late in the growing season, being short branches with crowded internodes. 



In pools, tanks and small streams, throughout most of Okla., common in e. 

 Tex. and in the mts. of the Trans-Pecos to Ariz. (Coconino Co.), freely fruiting 

 throughout the summer; mostly in s. U.S. and Mex. 



Var. trichophyllus Morong. Similar to var. diversifolius except submersed 

 leaves flaccid, setaceous or setaceous-linear, 0.1-0.6 mm. wide, tapering to an 

 acute r x, the nerves 1 or obscurely 3; stipules delicate, free or partially adnate 

 to the oase of the leaf blade, deciduous with age; floating leaves lance-elliptic 

 to oval-elliptic, acutish or (if rounded) at least submucronate at apex; blades 

 7-26 mm. long. 1—10 mm. wide; nerves 3 to 9; stipules 3-10 mm. long; peduncles 

 1-4 mm. long from the axils of submersed leaves and 2-30 mm. from the axils 

 of the floating leaves; fruits with dorsal keel entire or with 3 to 12 small teeth. 

 In the same habitats as var. diversifolius. 



10. Potamogeton pulcher Tuckerm. Fig. 40. 



Rhizome pale-buff", often with dark-red spots; stem simple, terete, 1-2.5 mm. 

 in diameter, usually conspicuously dark-spotted; stele with the prototype pattern; 

 endodermis of 0-cells; interlacular and subepidermal bundles absent; pseudo- 

 hypodermis mostly 1 cell thick; submersed leaves of two intergrading types, those 

 of the lower part of the stem semiopaque and oblong with rounded apices, those 

 of the upper part of the stem translucent and lanceolate to lance-linear, with an 

 acutish but not sharp-pointed apex, both types tapering at base to petioles to 35 

 mm. long; blades entire, to 18 cm. long and 35 mm. wide, usually smaller; nerves 

 11 to 21, the outer ones marginal; lacunae 4 to 8 rows on each side of midrib; 

 floating leaves coriaceous, ovate to rotund, rounded to bluntly mucronate at apex, 

 cordate or rounded at base; petioles 4-18 cm. long; blades to 11 cm. long and 

 85 mm. wide, with 19 to 35 nerves; stipules of the submersed leaves decaying 

 early, those of the floating leaves persistent, narrowly triangular, obtuse when 



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