Pennsylvanian Tree Fern Compressions 



Caulopteris, Megaphyton, and 



Artisophyton gen. nov. in Illinois 



Hermann W. Pfefferkorn* 



ABSTRACT 



Compression-impression fossils of tree fern 

 stems often exhibit the configuration of the vascu- 

 lar bundle of the leaf petiole. The shape of the 

 trace is one of the major criteria used to distin- 

 guish higher taxa (genera or even families) among 

 the tree ferns. Thus compression-impression fos- 

 sils can yield information on the natural classifi- 

 cation of these stems. 



Two distinct configurations of the vascular 

 bundle are known from tree fern stems of Pennsyl- 

 vanian and Mississippian age. One is a sequence of 

 shapes from horseshoe-shape to a closed oval con- 

 taining one internal trace. This sequence occurs 

 on stems with four or more rows of leaf scars in 

 the genus Caulopteris Lindley and Hutton, 1832. It 

 is also found in stems with only two rows of leaf 

 scars in the mature stem; these stems are called 

 Megaphyton Artis, 1825. 



The other configuration of the vascular 

 bundle is a sequence of shapes from a closed rec- 

 tangular external trace having a deeply indented 

 abaxial side and one internal trace to a stage in 

 which two external traces, each containing one in- 

 ternal trace, have formed. An intermediate stage 

 of the sequence is an external rectangular trace, 

 also indented, with two internal traces. This se- 

 quence is found only on stems with two rows of leaf 

 scars. To separate this sequence from Megaphyton, 

 which also has two rows, a new genus, Artisophyton, 

 is proposed in this paper. 



Size, form, and arrangement of the leaf 

 scars are so varied that it is uncertain whether 

 natural species can be established within these 

 three genera. It is suggested here that the 

 height to width ratio in relation to the size is 

 adequate to delineate form-species. In Illinois 

 several form-species of Caulopteris, one form- 

 species of Megaphyton, and two form-species of 

 Artisophyton are known. 



*Present address: Department of Geology, University of Pennsylvania, Philadelphia, 

 PA 191714-. 



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