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 ; 8 or 4 



carpU of each flower usually rim-nine . . 5. P. alplnwt. 



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

 A. Mature fruit 1.5-2 mm. long ....... 8. P. potygoni/oliut. 



a. Leaves all submersed and similar j. 

 j. Leaves lanceolate, oblong or broader k. 

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



1. leaves finely and sharply serrulate ...... 18. P. crittput. 



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



serrulate, margins m. 

 m. Mature spike 8.s>-5.5 cm. long. 



Fruit distinctly 3-keeled ........ 11. P. anyuttifoliut. 



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



m. Mature spike shorter n. 

 n. Spike more than 1 cm. long. 



Fol'.age and spikes strongly suffused with red ; 8 or 4 car- 



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



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

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



k. Leaves clasping or half-clasping o. 



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



stipules conspicuous and persistent ; fruit sharply keeled 

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



18. 



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. perfoliatut. 



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

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

 inconspicuous ......... 16. P. bupleur&idet. 



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 . . . 4. P. epihydrut. 



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 *. 

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



the principal leaves. 

 Peduncles equaling or exceeding the spikes . . . . 82. P. hybridv*. 



Peduncles shorter than the spikes ...... SB. P. dimorphut. 



t. 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-rfowered, in fruit 1.5-3 cm. long . . 19. P. eosterifcliu*. 

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

 u. Leaves with 3-7 nerves v. 

 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, mncronate; 



spikes subcylindric-ovoid ..... 22. P. obtutifoliut. 



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

 w. Bases of the leaves bearing translucent glands ; fruit 



plump, obscurely or bluotly keeled. 



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

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

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



keel or crest ..... (80) P.folionts, v. niagarennt, 



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

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

 branches Hosrly invested by imbricated leaves and 

 stipules y. 

 y. Winter-buds borne primarily on very short axillary 



branches. 



Leaves of the winter-buds widely divaricate . . 26. P. lattrulit. 

 Leaves of the winter-buds loosely ascending . . 27. P. Vasfyi. 

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



Leaves bristle-form, with very fine slender tips . . 28. P. gemmiparvt. 

 Leaves flat or revolute. acute or short-acuminate. 



Leaves rigid, revnlute : winter-buds 1-2 cm. long . 24. P. ttrictifoliut. 

 Leaves soft ; winter-buds about 1 cm. long . . 26. P. putilliu. 



