- 6 - 



6. Submersed leaves 0.1-0.6 mm wide, tapering to a long 

 point (fig. 6B) , lacunae not abundant; middle stem 

 leaves 190-500 times as long as broad; free portion 

 of stipule 3 or more times as long as the fused 

 portion; floating leaves (fig. 6A) , 3-7-veined, 

 the apicies acute. 

 5. Pjj_ bicupulatus 



6. Submersed leaves 0.5-2.0 mm wide, not long tapering; 

 lacunae abundant (fig. 8C) ; middle stem leaves 

 less than 190 times as long as broad; free portion 

 of stipule not more than twice as long as fused 

 portion; floating leaves 5-15-veined, the apicies 

 acute or obtuse (figs. 7A, 8A) . 



7. Tips of submersed leaves obtuse (fig. 7E) ; 

 fruit 1.3-2.2 mm wide, lateral keels scarcely 

 developed (fig. 7D) , or rarely well developed 

 (fig. 7C) , beak lacking. 

 6. Pj^ spirillus 



7. Tips of submersed leaves acute (fig. 8B) ; 

 fruit 1.0-1.5 mm wide, lateral keels well 

 developed, minute beak present (fig. 8D) . 

 7. Pjj^ diversifolius 



1. Plants with stipules completely free (figs. 14C, 15D, 18B) . 



8. Submersed leaves linear, with parallel margins, 0.1-10.0 

 mm wide (figs. 9A, IIC, 12A) . 



9. Lacunae prominent in submersed leaves (figs. 9D, 

 lOB) , 2-10 mm wide; floating leaves often present; 

 fruit with keel 0.2-1.2 mm broad. 

 8. Pj^ epihydrus 



9. Lacunae not prominent in submersed leaves, 



(except in some specimens of P^^ pusillus var. 

 tenuissimus ) , 0.1-3.2 mm wide; fruit with keel less 

 than 0.2 mm broad. 



10. Floating leaves absent. 



11. Rhizome long and creeping (fig. IIA) ; 

 peduncle 15-24 cm long (fig. HA); leaves 

 thread-like (fig. 11A,C) , 0.1-0.5 mm wide. 

 9. Pj^ confervoides 



11. Rhizome short or lacking; peduncle 0.3-10 



cm long, often curved (figs. 13A, 14A) ; 



leaves usually not thread-like (figs. 



12-19) [except in P^ pusillus var. 



gemjniparus (fig. 20)], 0.1-3.2 mm wide. 



12. Nodal glands absent (fig. 14C) . 



13. Leaves 15-25-veined (fig. 12B) , 



