NAJADACEAE (PONDWEED FAMILY) 



71 



i. Mature spikes 1.5-3.5 cm. long (if rarely longer, with float- 

 ing leaves 10-18-nerved). 

 Foliage and spikes strongly suffused with red ; 3 or 4 



carpels of each flower usually ripening . . . 5. P. 

 Foliage and spikes greenish ; 1 (rarely 2) carpels ripening 10. P. 



h. Mature fruit 1.5-2 mm. long 3. P. 



a. Leaves all submersed and similar j. 

 j. Leaves lanceolate, oblong or broader k. 

 k. Leaves sessile or short-petioled, not clasping I. 



1. Leaves finely and sharply serrulate 18. P. 



I. Leaves entire, but sometimes with puckered or undulate, not 



serrulate, margins m. 

 m. Mature spike 3.8-5.5 cm. long. 



Fruit distinctly 3-keeled 11. P. 



Fruit with rounded, scarcely keeled sides . . . . 12. P. 

 m. Mature spike shorter n. 



n. Spike more than 1 cm. long. 



Foliage and spikes strongly suffused with red ; 8 or 4 car- 

 pels of each flower usually ripening . . . 5. P. 

 Foliage and spikes greenish ; 1 (rarely 2) carpels ripening 10. P. 



n. Spike 4-7 mm. long 17. P. 



k. Leaves clasping or half-clasping o. 



o. Leaves half-clasping, elongate, with rounded cucullate tips ; 

 stipules conspicuous and persistent ; fruit sharply keeled 



alpinus. 



heterophyllus. 



polygonifolius. 



angustifoUus. 

 lucens. 



alpinus. 



heterophylhta. 



mysticus. 



13. P. praelongus. 



16. P. buplewoides. 

 epihydrus. 



4. P. 



o. Leaves cordate-clasping, if elongate with tapering plane tips ; 

 stipules inconspicuous or soon reduced to shreds; fruit 

 rounded on the back or obtusely keeled p. 

 p. Leaves undulate or crisped, with 3-7 prominent nerves ; fruit 



3.5-4.5 mm. long. 



Stipules 1-2 cm. long, persisting as shreds; leaves lance- 

 attenuate 14. P. Richardsonii. 



Stipules short and inconspicuous ; leaves from suborbicular 



to oblong-lanceolate 15. P. perfoliatus. 



p. Leaves flat, scarcely crisped, with 1 prominent nerve; fruit 

 2.5-3.2 mm. long; stipules, when developed, short and 



inconspicuous 



j. Leaves linear to setaceous q. 



q. Leaves ribbon-like, 2 mm. or more wide, with a broad coarsely 



cellular-reticulate space each side of the midrib .... 



q. Leaves narrower, if occasionally 2 mm. wide, without a broad 



cellular-reticulate space r. 



r. Leaves free from the stipules, or, if slightly ad n ate to them, 

 bearing globose subsessile or short-stalked spikes in their 

 axils s. 

 s. Fruit flat, cochleate ; the globular spikes borne in the axils of 



the principal leaves. 

 Peduncles equaling or exceeding the spikes . . . . 32. P. 



Peduncles shorter than the spikes 83. P. 



s. Fruit plump; spikes terminal or borne on the uppermost 



branches t. 



t. Principal leaves more than 1 mm. broad u. 

 u. Leaves with very many fine nerves. 



Spikes many-flowered, in fruit 1.5-3 cm. long . . 19. P. 

 Spikes 4-8-flowered, in fruit 5-8 mm. long . . .20. P. 

 u. Leaves with 3-7 nerves . 



v. Mature fruit 3.5-4.5 mm. long. 



Stipules 0.5-1 cm. long; leaves acute; spikes capitate 21. P. Hillii. 

 Stipules 1.2-2 cm. long ; leaves obtuse, mucronate ; 



spikes subcylindric-ovoid 22. P. obtusifolius. 



V. Mature fruit 2-3 mm. long w. 

 w. Bases of the leaves bearing translucent glands ; fruit 



hybridus. 

 dimorplws. 



zosterifoUiks. 

 acutifolius. 



plump, obscurely or bluntly keeled. 

 Leaves 5-7-nerved ; stipules 1-2 cm. 1 



long 



28. P. 

 25. P. 



Friesii. 

 pusillus. 



Leaves 3-nerved ; stipules less than 1 cm. long 

 w. Bases of leaves glandless ; fruit flattened, with a thin 



keel or crest (80) P.foUo8W,\.niagaren8i8. 



t. Principal leaves less than 1 mm. broad OD. 

 x. Plant bearing winter-buds formed by the hardened ends of 

 branches closely invested by imbricated leaves and 

 stipules y. 

 y. Winter-buds borne primarily on very short axillary 



branches. 



Leaves of the winter-buds widely divaricate . 

 Leaves of the winter-buds loosely ascending 

 y. Winter-buds borne at the tips of elongate branches. 

 Leaves bristle-form, with very fine slender tips . 

 Leaves flat or revolute, acute or short-acuminate. 

 Leaves rigid, revolute ; winter-buds 1-2 cm. long 

 Leaves soft ; winter-buds about 1 cm. long 



26. 



27. 



lateralis. 

 Vaseyi, 



28. P. gemmiparus. 



25. 



strictifotiits. 

 pusillus. 



