2(1). Each pistillate flower with 4 free carpels each of which at fruiting time is 



long-stipitate; submerged aquatics with linear leaves 



17. Ruppiaceae, p. 123 



2. Carpels either coalescent or if free then not stipitate (3) 



3(2). Carpels 2 to numerous, free from each other (4) 



3. Carpels solitary or if more than 1 then these (at base or throughout) coalescent 



for more than a third their length (7) 



4(3). Carpels numerous per female flower 21. Alismataceae, p. 133 



4. Carpels 2 to 9 per flower (5) 



5(4). Ovules numerous; flowers showy, yellow 22. Butomaceae, p. 153 



5. Ovules solitary; flowers inconspicuous (6) 



6(5). Perianth of 4 free rounded shortly clawed valvate segments 1-4 mm. long 

 15. Potamogetonaceae, p. 95 



6. Perianth absent (genus Zannichellia of) 16. Zannichelliaceae, p. 117 



7(3). Ovary inferior; perianth clearly epigynous (8) 



7. Ovary superior or apparently so, in some taxa the perianth reduced or absent, 



in some the perianth adnate to the ovary for a very short distance 

 basally (14) 



8(7). Partly or wholly submerged plants; ovules numerous, spread all over the 



inner surface of the carpels or on the intrusive septa 



23. Hydrocharitaceae , p. 156 



8. Plants not submerged or if partly so the ovules confined to placentary areas 



(9) 



9(8). At least the inner 3 tepals dissimilar to one another, the flower thus not 

 radially symmetrical (10) 



9. At least the inner 3 tepals (and usually the outer one, too) equal to each 



other or nearly so, the flower thus approaching true radial sym- 

 metry (12) 



10(9). Ovule solitary in each cell 39. Marantaceae, p. 686 



10. Ovules more numerous (11) 



1 l( 10). Flowers only slightly zygomorphic, reddish or orange, in terminal thyrses 

 on erect stems to 12 dm. tall 38. Cannaceae. p. 684 



11. Flowers strongly zygomorphic, the lower (or rarely uppermost) of the 3 



inner tepals strikingly diff"erent from the other 2, forming a label- 

 lum; stems usually less than 5 dm. long 41. Orchidaceae, p. 690 



12(9). Leaves equitant, distichous and folded along the midrib; stamens 3 



37. Iridaceae, p. 673 



12. Leaves not equitant: stamens 3 or 6 (13) 



13(12). Stamens 3; basal leaves usually linear and grasslike and stem or scape 

 leaves scalelike 40. Burmanniaceae, p. 686 



13. Stamens usually 6; basal leaves usually broader; plants very diverse in habit.... 



36. Ainaryllidciceae, p. 664 



14(7). Palmlikc plants with perennial stem 5-70 cm. thick at ground level and 

 lanlike leaves 4-12 dm. broad 26. Palinae, p. 555 



14. Habit otherwise ( 15) 



20 



