THE LIVING CYCADS AND THE PHYLOGENY OF SEED 
PLANTS! 
Charles J. Chamberlain 
Phylogeny is a big word and it can be made to cover most of the problems 
of relationship. Among the phylogenetic problems of a group, two always 
stand out prominently: "What has been its origin?" and "Has it left 
any progeny? " 
In the cycads these two problems are not equally difficult, for the origin 
can be traced back, with more or less certainty, to the ferns; but whether 
they have left any progeny is doubtful. However, if we stick close to the 
living cycads, it seems safe to claim that none of the nine genera has left 
any progeny or is likely to have any descendants. Like the higher members 
of the Cycadofilicales and Bennettitales, they are the last of their race; 
and if there should be another epoch succeeding the present, just as the 
present succeeded the Mesozoic, the Cycadales would become extinct, just 
as the Bennettitales became extinct. 
First let us consider the less difficult problem, the origin of the cycads. 
Just how far back the cycads extend, is a question which could be 
answered only by complete geological evidence; but what we know of 
available structures shows that the line goes back farther than any fossils 
yet discovered would indicate. 
A morphologist must depend largely upon comparative morphology in 
studying relationships, tracing each structure, geologically, from its earliest 
appearance, and tracing the ontogeny wherever material is available. 
The graphic method will illustrate clearly some of the principal features 
in the comparative morphology of cycads and at the same time will indicate 
their geological distribution (Plate VI). 
A very prevalent fern habit — a crown of pinnate leaves at the top of an 
unbranched stem — has been retained by the cycad line, with remarkable 
tenacity, from their earliest appearance up to the living forms. The armor 
of persistent leaf bases is another character which can be traced from the 
Paleozoic up to the living forms. The large pith, comparatively scanty 
zone of wood, and large cortex are features common to the living cycads, 
Bennettitales, and Cycadofilicales (Plate VI). 
If these three features — the crown of pinnate leaves, the unbranched 
stem with its armor of leaf bases, and the topography of a transverse section 
of the stem — were the only features worth considering, there could be little 
^ Invitation address read before the joint session of Section G, A. A. A, S., the Botanical 
Society of America, and the American Phytopathological Society, in the symposium on the 
"Phylogeny of Seed Plants," at St. Louis, December 30, 1919. 
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