Potamogeton PotamogetonaceaE 77 



D. Blades of leaves linear. 

 Leaves ribbonlike, 2 mm or more wide, with a broad, coarsely cellular-reticulate 



space on each side of the midrib, 5-7-nerved; stipules very obtuse 



14. P. epihydrus. 



Leaves narrower, if 2 mm wide, without broad cellular-reticulate spaces along 

 the midrib. 

 E. Blades free from the stipules. 



Leaves more than 7-nerved, 2-5 mm wide; peduncles stout, 1.5-5.5 cm long, 

 1-1.6 mm thick; fruit 3.5-5 mm long, with one strong, usually crested, 



keel on the back 15. P. zosteriformis. 



Leaves 1-7-nerved; fruit not more than 3 mm long. 



Blades 5-7-nerved, usually with a pair of glands at the base, 1.5-3.5 mm 

 wide, usually 2-2.5 mm wide, rounded or short-mucronate at the apex; 

 stipules 7-11 mm long; fruit 2-3 mm long, rounded on the back. 



16. P. Friesii. 



Blades 1-3-nerved (if some leaves 5-nerved, plant not agreeing with the 

 other characters of the preceding species). 

 Leaves 1-nerved (under high magnification 3-nerved) ; fruit strongly com- 

 pressed with the sides almost fiat, 1.6-2.2 mm long. (See excluded 



species no. 32, p. 1024.) P- Vaseyi. 



Leaves 3-nerved, rarely some of them 5-nerved. 



Blades usually without basal glands; peduncles 0.4-3 cm long, clavate; 

 spikes subcapitate, 2-6-flowered, in fruit 2-8 mm long; sepaloid con- 

 nectives 0.4-1 mm long; fruit compressed, 1.8-2.5 mm long, with a 

 thin or acute, undulate or coarsely dentate dorsal keel. 

 Primary leaves 4-10 cm long, 1.4-2.7 mm wide, 3-5-nerved, midnerve 

 with 1-3 rows of lacunae on each side at the base; stipules 0.7-1.8 

 cm long; fruit 2-2.5 mm long, beak broad at the base, 0.2-0.4 mm 

 long; winter buds sessile in the axils or on short (rarely elon- 

 gate) branches 17. P. foliosus var. genuinus. 



Primary leaves 1-7 cm long, 0.3-1.5 mm wide, 1-3-nerved; midnerve 

 without marginal lacunae or with a single row on each side below 

 the middle; stipules 3-11 mm long; fruit green, 1.8-2.3 mm long, 

 beak slender, 0.3-0.8 mm long; winter buds terminating the mostly 



elongate branches 17a. P. foliosus var. macellus. 



Blades usually with a pair of basal glands; peduncles 1-9 cm long; spikes 

 interruptedly cylindric, of 2-5 remote whorls of flowers or sub- 

 globose, in fruit 0.6-1.5 cm long; sepaloid connectives 1-2.5 mm 

 long; fruit plump, 1.9-3 mm long, rounded on the back, dorsal keel 

 obscure. 

 Spikes subglobose, continuous or slightly interrupted, 2-8 mm long in 



fruit ; leaves 3-7 cm long, rounded or acute at the apex 



18. P. pusillus var. mucronatus. 



Spikes cylindric, of 2-5 remote whorls of flowers, in fruit 0.6-1.5 cm 

 long. 

 Stipules strongly fibrous, becoming whitish. 



Leaves mostly rigid, obtuse or abruptly contracted to muci-onate 



tips ; stipules strongly fibrous 



19. P. striotifolius var. typicus. 



Leaves firm, scarcely rigid, very gradually tapering to a slender 



tip ; stipules less strongly fibrous 



19a. P. striotifolius var. rutiloides. 



Stipules scarious-membranaceous or subherbaceous, greenish or 

 brownish. 



Primary leaves 1-3 mm wide 20. P. panormitanus var. major. 



Primary leaves only 0.3-1 mm wide 



20a. P. panormitanus var. minor. 



