CHAPTER XII 



CLASSIFICATION OF SYMPETALAE 



THE Sympetalae form a much better defined group than do 

 the Archichlamydeae, from which they seem to have been de- 

 rived. The sympetalous character is almost universal, and 

 justifies the name of the group. To regard it as the crucial 

 test, however, is to introduce the flavor of an artificial system. 

 Among the Archichlamydeae sympetalous forms were noted, 

 and certain families of the Sympetalae include polypetalous 

 members. It would seem that such exceptions might apply to 

 whole families, whose other characters would determine their 

 affinities. For example, the Umbelliferae present the combina- 

 tion of characters that belongs to the Sympetalae, excepting 

 sympetaly; and this exception does not seem to be a sufficient 

 reason to exclude them from association among the epigynous 

 anisocarpic Sympetalae, any more than the polypetaly of the 

 Pirolaceae excludes them from the isocarpic Sympetalae. 



The general characters of Sympetalae are (1) a complete 

 cyclic arrangement of the floral members, associated with defi- 

 nite numbers; (2) a sympetalous corolla that usually has a 

 common origin with the stamens; and (3) ovules with a single 

 massive integument and a very small nucellus. The group con- 

 tains fifty-one families, the number varying with different au- 

 thors, and about 42,000 species, or approximately two-thirds 

 of the number included in the Archichlamydeae. Eight alli- 

 ances have been recognized by Engler," coordinate with the ten 

 alliances of Monocotyledons and the twenty-six alliances of 

 Archichlamydeae, the contrast with the latter group in uniform- 

 ity of floral structure being very striking. 



The natural sequence of the alliances is much more evident 

 than among the Archichlamydeae. The first three alliances are 

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