NAJADACEAE (PONDWEED FAMILY) 



71 



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

 ing leaves 10-lS-nerved). 

 Foliage and spikes strongly suffused with red ; 3 or 4 



carpels of each flower usually ripening 

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



h. Mature fruit 1.5-2 mm. long 



a. Leaves all submersed and similar j. 

 j. Leaves lanceolate, oblong or broader k. 

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



/. . Leaves finely and sharply serrulate 



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 



Fruit with rounded, scarcely keeled sides .... 

 . Mature spike shorter n. 

 .. Spike more than 1 cm. long. 



Foliage and spikes strongly suffused with red ; 3 or 4 car- 

 pels of each flower usually ripening 

 ' (rar 



5. P. 

 10. P. 

 3. P. 



alpinus. 



heterophyllus. 



polygonifolius. 



18. P. crispua. 



11. P. 



12. P. 



angustifoHus. 

 lucens. 



alpinus. 



heteropliyllus. 



mysticus. 



16. P. buplewoides. 

 epihydrus. 



4. P. 



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



n. Spike 4-7 mm. long 



k. Leaves clasping or half-clasping o. 



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



stipules conspicuous and persistent ; fruit sharply keeled . 13. P. praelongus. 

 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. JRichardsonii. 



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 adnate to them, 

 bearing globose subsessile or short-stalked spikes in their 

 axils .v. 

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



the principal leaves. 

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



Peduncles shorter than the spikes 33. P. dimorphus. 



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



branches t. 



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

 it,. Leaves with very many fine nerves. 



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

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

 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. ffillii. 

 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 



plump, obscurely or bluntly keeled. 



Leaves 5-7-nerved ; stipules 1-2 cm. long . . 28. P. Friesii. 

 Leaves 3-nerved ; stipules less than 1 cm. long . 25. P. pusillus. 

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



keel or crest (30) P. foliosus, v. niagarensis. 



t. Principal leaves less than ] mm. broad x. 

 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 



y. 



Leaves of the winter-buds loosely ascending 

 Winter-buds borne at the tips of elongate branches. 



Leaves bristle-form, with very fine slender tips . 



Leaves fiat or re volute, acute or short-acuminate. 

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

 Leaves soft ; winter-buds about 1 cm. long 



26. P. 



27. P. 



lateralis. 

 Vaseyi. 



28. P. gemmiparus. 



strictifolius. 

 pusillus. 



'24. 



'25. 



