26 Key to the Families 



GYMNOSPERMAE 



Flowers solitary, axillary; seed solitary, enveloped in a pulpy disk (berry- 

 like) 5. Taxaceae, p. 66. 



Flowers borne in catkins; fruit a cone or a several-seeded berry 



6. Pinaceae, p. 66. 



Ovules borne in a closed ovary which, at maturity, becomes the fruit; herbs or 

 woody plants, with broad or narrow, evergreen or deciduous leaves (Angio- 

 sperms) J. 



ANGIOSPERMAE 



J. Embryo with a single cotyledon; early leaves always alternate (leaves some- 

 times whorled), mostly parallel-veined (net-veined in Araceae and Dios- 

 coreaceae; parts of the flower in threes or sixes, never in fives; stems with- 

 out a central pith or ringlike layers, but with woody fibers distributed 

 through them ; our species, except in the genus Smilax, herbaceous ( Monocoty- 

 ledons) K. 



MONOCOTYLEDONEAE 



K. Plant scarcely differentiated into stem and leaf, small, usually lens-shaped, 



ellipsoid or oblong; free-swimming aquatics without true leaves 



24. Lemnaceae, p. 279. 



K. Plant with stem and leaves L. 



L. Perianth free from the ovary or none M. 



M. Perianth lacking, or of scalelike or bristle-form divisions N. 



N. Flowers enclosed or subtended by scales (glumes) ; plants grasslike, 

 with jointed stems, sheathing leaves, and 1-seeded fruit. 

 Stems hollow, round or flattened; leaf sheaths split; anthers attached 



at the middle 19. Gramineae, p. 93. 



Stems solid, usually more or less triangular; leaf sheaths not split; 



anthers attached at the base 20. Cyperaceae, p. 181. 



N. Flowers not enclosed in scales (though sometimes in involucrate 

 heads) O. 

 O. Plants immersed aquatics, branching and leafy, the upper leaves 

 often floating. 



Leaves opposite or ternate; pistils solitary, naked 



12. Najadaceae, p. 84. 



Leaves alternate or 2-ranked; pistils aggregated into heads or 

 clusters. 

 Fruit in heads, the nutlets composing it tightly compact, with 



prominent, conical style bases mostly 2-4 mm long 



10. Sparganiaceae, p. 72. 



Fruit in clusters; nutlets not tightly compact, the style bases 

 usually short or very slender 



11. POTAMOGETONACEAE, p. 75. 



O. Plants terrestrial or of a marsh habitat. 



Leaves petiolate, the blades net-veined 23. Araceae, p. 277. 



Leaves not petiolate, linear or sword-shaped, parallel-veined P. 

 P. Flowers monoecious or dioecious. 



Flowers and fruit in a cylindrical spike. . .8. Typhaceae, p. 71. 

 Flowers and fruit in heads. 



Heads spheroidal, pubescent, involucrate 



30. Eriocaulaceae, p. 283. 



Heads globose, glabrous, not involucrate 



10. Sparganiaceae, p. 72. 



