PTEROPSIDA 141 



6. large spore output, 7. prothallus long lived, 8. massive 

 antheridium, 9. suspensor present in some, absent in others. 

 Characters which suggest that the two groups are only 

 distantly related are the circinate vernation of the Maratti- 

 ales and their superficial sori, contrasting with the absence 

 of circinate vernation from the Ophioglossales and their 

 marginal sporangia. 



Osmundidae 



Osmundales 

 Osmundaceae Zalesskya^ ^ Thamnopteris^ ^ Osmundites"^, 



Osmunda, Todea, Leptopteris 



The modern representatives of the Osmundales occupy an 

 isolated position among the ferns, intermediate in many 

 respects between the Eusporangiatae and the Leptosporan- 

 giatae but not necessarily, therefore, finking the two groups 

 phylogenetically, for they are an extremely ancient group 

 with an almost complete fossil history extending as far 

 back as the Permian. Those that have survived to the 

 present day can truly be described as 'living fossils'. 



All have erect axes, bearing a crown of leaves ; and the 

 same is true of the fossil members, some of which had trunks 

 I m or more in height. Among the earliest representatives, 

 in the Permian, were several species of Zalesskya. These had 

 a sofid protostele in which there were two distinct regions of 

 xylem (an inner region of short tracheids and an outer one 

 of elongated tracheids forming an unbroken ring). The same 

 was true of Thamnopteris Schlechtendalii, but T. Kidstonii 

 had a sfightly more advanced stelar anatomy, in that the 

 central region was occupied by a mixed pith of tracheids 

 and parenchyma. Osmundites Dunlopii from the Jurassic 

 was similar to T. Kidstonii, but the contemporaneous O. 

 Gibbeana showed some dissection of the xylem ring into 

 about twenty separate strands.*^ Nevertheless, the stele was 

 still strictly a protostele, since there was a continuous zone 



