CHAPTER III 

 CYCADALES 



The living cycads form a small natural group containing only 

 nine genera and less than one hundred species, all of which are tropical 

 or subtropical. Four of the genera belong exclusively to the western 

 hemisphere and the other five to the eastern. 



Of the western genera, Zamia contains about thirty species and 

 ranges from southern Florida to Chili. The three other genera are 

 very limited both in number of species and in distribution: Micro- 

 cycas is monotypic and confined to western Cuba; Dioon, with three 

 species, is found only in southern Mexico; and Ceratozamia, with 

 two or perhaps more species, has about the same range as Dioon, with 

 which it is associated in some localities. 



Of the five eastern genera, Cycas is the most prominent, both in - 

 number of species and in distribution, its sixteen species ranging 

 from Japan to Australia. The four other genera are very restricted : 

 Macrozamia, with fourteen species, and the monotypic Bowenia 

 belong to Australia; while Encephalartos, with twelve species, and 

 Stangeria, with two or more species, belong to southeastern Africa. 



The genera are sharply defined, but such species as are based only 

 upon leaf characters are open to suspicion, because the leaves vary 

 greatly with the age of the plant. In 1901, when the first edition of 

 this book was written, little was known of the morphology of any 

 of the cycads except the widely ranging and consequently easily 

 accessible Cycas and Zamia. Since then, Dioon, Ceratozamia, and 

 Microcycas have been studied, so that the life histories of all the occi- 

 dental genera are quite w'ell known. Some additional information 

 in regard to the oriental genera is also available, but many important 

 features in the life histories of the Australian and African forms are 

 still unknown. This increased knowledge of the cycads themselves, 

 together with extensive studies of the Cycadofilicales and Bennettitales, 

 allows a more satisfactory presentation of the group than was possible 

 a few years ago. 



The cycads are distinguished from the other living gymnosperms 



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