PENNSYLVANIA TREE FERN COMPRESSIONS 



13 



There is, to my knowledge, no structurally preserved material 

 that can be attributed to Artisophyton. Information on the systematic 

 position of Artisophyton is therefore restricted to circumstantial 

 evidence. 



Corsin (1948) made the point that Artisophyton (he called it 

 Megaphyton) probably bore foliage of the Pecopteris plumosa-P. pennaeformis 

 group, which bears Senftenhergia sporangia. His reasoning was as follows. 

 The vascular trace in Artisophyton divides into two independent traces 

 (text fig. 4). This division most probably indicates a forking of the 

 rachis of the frond relatively close to the stem. This feature occurs 

 in several groups of Pennsylvanian plants, including some pteridosperms , 

 some coenopterids , and the Pecopteris plumosa-P. pennaeformis group. 

 The pteridosperms with forked fronds and the coenopterids with forked 

 fronds have totally different types of vascular bundles from those of 

 Artisophyton. Thus the only possibility left among the known groups with 

 forked fronds is the Pecopteris plumosa-P. pennaeformis group. Further- 

 more, P. plumosa and the related species that have very large fronds occur 

 in the same beds as Artisophyton, which had leaf scars up to 12 cm in 

 diameter. This association of P. plumosa and related species with Artiso- 

 phyton occurs in northern France as well as in Illinois. Thus there is 

 at least a possibility that Artisophyton stems bore Pecopteris plumosa 

 foliage with Senftenhergia sporangia. 



Senftenhergia has been classified with the Schizeaceae on the 

 basis of the structure of the sporangia. Jennings and Eggert (1972) 

 investigated the anatomy of Senftenhergia and its foliage and considered 

 the genus a coenopterid fern. It could follow that there were coenop- 

 terid tree ferns in Pennsylvanian time. 



Differences Between Species 



The characteristic widely used in differentiating the 100 species 

 of Caulopteris and the 43 species of Megaphyton and Artisophyton (number 

 of species from the "Fossilium Catalogus," Jongmans and Dijkstra, 

 1959, 1961) was the small vari- 



ation in the shapes of the vascu- 

 lar bundle. Renault and Zeiller, 

 1888 (seen in Andrews and Doubin- 

 ger, 1970), however, described a 

 specimen of Caulopteris varians 

 that showed different configura- 

 tions of the vascular bundle on 

 one stem. Recently Stidd (1971) 

 demonstrated that different shapes 

 of the leaf traces in Psaronius 

 occur in the basal part of the 

 same rachis (text fig. 10). In 

 earlier publications, the spec- 

 imens represented in text figure 

 10, A to F, would have been 

 treated as six species. Now that 

 these different vascular configu- 

 rations have been recognized as 

 developmental stages, it is clear 

 that they do not necessarily 



QCA 



Text fig. 10 - Configuration of vascular 

 bundle in leaf scars of Caulopteris 

 and Megaphyton and the supposed devel- 

 opmental sequence in the basal part of 

 a rachis. A is closest to the point 

 of origin. Dotted line is outline of 

 leaf scar. Sequence A to D is stewar- 

 tiopteroid and sequence A, B, E, F is 

 stipitopteroid . 



