12 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 492 



four stem genera can be recognized: Caulopteris, Megaphyton, Hagio- 

 phyton, and Artisophyton. The stem genera are shown diagrammatically 

 in text figure 9. 



Megaphyton has often been defined only by the distichous posi- 

 tion of the leaf scars without regard to the form of the vascular 

 bundle. Thus specimens called Megaphyton often included species with 

 horseshoe-shaped traces as well as those with closed traces having an 

 indentation as shown in text figure 4. However, differences in config- 

 uration of traces are much more meaningful for a systematic subdivision 

 than is the distichous arrangement of the scars. Therefore, the genus 

 Megaphyton must be divided. Artis (1825) described Megaphyton as 

 having "cicatrices near together, horseshoe-shaped with the points 

 upwards" (explanation of plaLe 20). The plate itself, however, does not 

 show this feature clearly. Similar circumstances surround the first 

 description of Zippea by Corda (1845). Even though the figure of the 

 type species of Zippea disticha does not show any trace of a vascular 

 bundle, Corda (1845) stated that he had other specimens which show a 



horseshoe-shaped trace, and he 



Top 



Caulopteris 



B Megaphyton 



Top 



Hagiophyton 



Artisophyton 



Text fig. 9 - Diagrammatic drawings of the 

 compression- impression genera of stems 

 of tree ferns of Pennsylvanian age. 



illustrated the trace with a 

 drawing. Corda f s specimen is 

 interesting because some internal 

 features can be seen. The stems 

 are preserved in sandstone and 

 are still round. The outline of 

 the vascular bundle is visible as 

 a band of carbon in the cross sec- 

 tion of the stem. The vascular 

 bundles are band shaped like those 

 in Psaronius. 



For the stems which have 

 in their leaf scars a configuration 

 of the vascular bundle as shown 

 in text figure 4, the new name 

 Artisophyton is used. 



Hagiophyton is very similar 

 to Megaphyton and might well be a 

 synonym of it. The only difference 

 is that in Hagiophyton, as described 

 by Corsin (1948), a sclerenchymous 

 band surrounds the vascular trace. 



Natural Systematics 



Internal structures have 

 been found in connection with speci- 

 mens of Caulopteris and Megaphyton. 

 Therefore it is established and well 

 known that these two genera belong 

 to the Psaronius group and can be 

 classified as Marattiaceae. 



