CHAPTER XI 



CLASSIFICATION OF ARCHICHLAMYDEAE 



Two great divisions of Dicotyledons are evident, the Archi- 

 chlamydeae and Sympetalae, although there is no sharp distinc- 

 tion between them. Sympetalous forms among the former and 

 polypetalous forms among the latter occur, but in the main 

 apetaly or polypetaly is a distinctive feature of the Archichla- 

 mydeae, and sympetaly of the Sympetalae. That the Arehi- 

 chlamydeae include the most primitive Dicotyledons is clear, 

 but what forms are to be regarded as the most primitive is open 

 to discussion. 



The classification of the Archichlamydeae is an exceedingly 

 puzzling problem, and the current schemes are far less definite 

 and satisfactory than those for the classification of Monocotyle- 

 dons and Sympetalae. Questions of primitive and reduced 

 characters, and of relative rank on the basis of combination of 

 characters, are particularly involved among Archichlamydeae, 

 and hence opinions vary widely as to the details of their classi- 

 fication. The difficulties arise from the fact that the characters 

 of the group are extremely fluctuating, not being established 

 as among the Sympetalae. Add to this that more than 60,000 

 species * are recognized, over three times as numerous as the 

 species of Monocotyledons, included in ISO families, and it 

 becomes evident that the confusion of relationships is bewil- 

 dering. 



Engler has arranged the Archichlamydeae in twenty-six al- 



* The numbers of species given in I In- chapter musl be regarded as approx- 

 imate mnl conservative. They will vary with the increase of knowledge and 

 the conception of species, bu1 in this chapter they are only intended to indi- 

 cate I lir relative display of different t ypes of structure. 

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