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 Chih. 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 Austraha. 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 one 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, 

 Microcycas, and Stangeria have been studied rather thoroughly, and 

 some phases of the life history have been examined in the remaining 

 genera. Besides, all the genera and about half of the species have 

 been studied in the field, so that considerable additional information 

 is available. 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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