24. Leaves tristichous; each floret subtended by a single abaxial scale (seemingly 



2 scales in Hemicarpha, or by a sac in Carex, or by bristles in addi- 

 tion to the scale in some genera) 25. Cyperaceae, p. 341 



25(19). Calyx irregular, glumaceous, the 2 persistent lateral sepals cymbiform 

 and dorsally keeled or winged, the third sepal larger, obovate and 

 enfolding or forming a hood over the corolla in bud and deciduous 

 with it 30. Xyridaceae, p. 578 



25. Calyx otherwise (26) 



26(25). The 3 inner tepals (petals) quite distinct in color and/ or texture from 

 the 3 outer ones (sepals) (27) 



26. The 6 tepals all rather similar in color and texture, either all dry and scale- 



like or all corolline (28) 



27(26). Ovary completely 3-celled; lower part of leaves sheathing the internodes 

 32. Commelinaceae, p. 593 



27. Ovary incompletely 3-celled or 1-celled; leaves not sheathing 



29. Mayacaceae, p. 578 



28(26). Perianth of 6 scalelike dry brown noncorolline tepals 



34. Juncaceae, p. 604 



28. Perianth of 6 corolline tepals or with 6 corolline segments (29) 



29(28). Usually floating, partly submerged or at least rooting in mud; inflores- 

 cence subtended by spathelike leaf sheaths; seeds usually ribbed; 

 flowers usually somewhat zygomorphic....33. Pontederiaceae, p. 597 



29. Dryland to marshland plants; inflorescence usually not subtended by a 



spathelike leaf sheath; seeds various, usually not ribbed; flowers 

 almost always radially symmetrical 35. Liliaceae, p. 646 



IV. Dicotyledoneae (p. 734 of text) 



1. Flowers with all the petals united at their edges (at least near the base) into 

 a single structure, this corolla often deciduous as a unit and often 

 shaped like a saucer, a cup or a trumpet (2) 



1. Flowers not as above, if any petals joined then not all of them involved or 



else not joined at their edges (occasionally the petals may seem 

 to be joined somewhat in bud but not in the mature flower), or 

 petals absent (48) 



2(1). Flowers epigynous or partly so, i.e., the perianth and stamens when pres- 

 ent appearing to be attached to the top or near the middle of the 

 sides of the ovary (3) 



2. Flowers hypogynous or perigynous, the sides of the ovary free from the peri- 



anth or the floral cup, the perianth attached below the ovary (12) 



3(2). Anthers 5 or 4, coalescent but filaments free (anthers exceptionally free 

 in the genera Ambrosia, Xanthium, Iva); fruit an achene and usu- 

 ally crowned by the modified calyx of bristles or scales; style 

 branches usually 2, usually divergent; flowers usually very small 

 and aggregated in involute heads 129. Compositae, p. 1586 



3. Anthers usually free (exceptions: Curcurbitaceae; 1 genus of Campanulaceae); 



fruit diverse but rarely an achene (exception: Valerianaceae); style 

 branches 1 to 20; flowers rarely aggregated in involucrate heads (4) 



23 



