Psilophytopsida 



Extinct plants. Only the sporophyte is known. 

 Rootless, with rhizomes and aerial branches that 

 are more or less dichotomous, either naked or 

 with small appendages spirally arranged. Proto- 

 stelic. Sporangia thick-walled, homosporous, borne 

 at the tips of branches. 



Psilophytales* 

 Rhyniaceae* Rhynia* Horneophyton* {=Hornea), 



Cooksonia,* Yarravia* 

 Zosterophyllaceae * Zosterophyllum * 

 Psilophytaceae* Psilophyton* 

 Asteroxylaceae* Aster oxylon* 



The first member of this group ever to be described was 

 Psilophyton princeps in 1859^^, but for many years httle 

 notice was taken of this discovery. Indeed, many botanists 

 regarded it almost as a figment of the imagination, so differ- 

 ent was it from their preconceived ideas of land plants. 

 However, by 19 17 Kidston and Lang^° had started to des- 

 cribe a number of similar plants from Middle Devonian 

 rocks at Rhynie in Scotland, and it became accepted that 

 plants with such a simple organization had really existed. 

 Only then was the group Psilophytales created to include 

 them. 

 The chert deposits at Rhynie, some eight feet thick, are 



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