THE DISTRIBUTION OF DRYOPTERIS BORRERI NEWM. IN THE 



BRITISH ISLES 



By J. P. PuGH 



Introduction 



The fern that has been called Dryopteris filix-mas var. paleacea has been well known 

 to botanists for many years. Manton (1950, 54) has given reasons for raising this fern 

 to specific rank as suggested by Newman (1854, 189) and the plant is now known as 

 Dryopteris borreri Newm. in Britain. This work was undertaken with a view to determining 

 the distribution of D. borreri in the British Isles, correlating this with its distribution on 

 the continent, and comparing it with the distribution of D. filix-mas. A general 

 account is given in this paper ; detailed cytological work has been started and will be 

 reported at a later date. 



Description of D. borreri Newm. 



The distinguishing characters of D. borreri are : — 



(1) The large number of ramenta (scales) extending along the abaxial side of the 

 rhachis of the frond from base to apex, which tend to be red-brown in 

 colour as opposed to those of D. filix-mas which are far less abundant and 

 yellow-brown in colour. 



(2) The pinnules tend to be truncate and less toothed than those of D. filix-mas 

 and also they are incompletely separated at the base (fig. 1). 



Fig. 1. Ventral view of pinnules of D. borreri (left) and D. filix-mas (right) ( X2). 



(3) The fronds of D. borreri tend to be tougher than those of D. filix-mas, persisting 

 long into the autumn and often overwintering. 



(4) In the spring the indusium is tucked under the edges of the sorus, whereas 

 in D. filix-mas the indusium lies flat on the surface of the frond around the 

 sorus (fig. 2). 



(5) Fresh specimens exhibit a small area of black pigment at the base of the 

 pinna rhachis where it joins the main rhachis of the frond. This pigment is 

 absent in herbarium specimens and has been found to disappear within a 

 month of collection. 



(6) D. borreri reproduces apogamously, the sporophyte arising directly from 

 the tissues of the gamctophyte without the formation of archegonia. Hence 

 there is no sexual fusion, although fertile male gametes may be formed. 

 Reproduction is quite normal in D. filix-mas. 



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