CHAPTER 6 



THE OTHER BRITISH FERNS: POLTSTICHUM, 

 ATHTRIUM, ASPLEJVIUM, CETERACH 



The British fern flora, a quarter of which has now been passed in review, is less than a 

 hundredth part of the ferns of the world, yet it is fortunately sufficiently varied to serve 

 as a qualitative sample of ferns in general provided always that the whole of it is studied.* 

 This can perhaps best be shown by a diagrammatic reproduction of Bower's phyletic 

 views (Fig. 74), from which it will be seen that of the six major groups into which the 

 leptosporangiate ferns are divided only one, the 'Davallioids', is wholly without a 

 British representative. It should perhaps be pointed out that only the higher ferns are 

 included in this scheme, the more primitive ones comprising the Eusporangiatae, 

 Hymenophyllaceae and the Osmundaceae being more conveniently deferred to the 

 end of the book. All the other British genera and every British species in each will, 

 however, now be reviewed in this and the two following chapters, and if again the 

 narrative at times resembles a catalogue apology can no longer be made for it is of the 

 essence of a sample that it should be within its hmits complete but composed of varied 

 and, if necessary, unconnected elements. 



It may, however, be helpful in maintaining a thread of continuity with the two 

 preceding chapters if we begin our wider survey with the remaining British genera of the 

 'Dryopteroid' affinity. This, as a glance at the diagram will make clear, contains four 

 other genera and two doubtful ones in addition to ' Dryopteris\ and to the first of these, 

 namely Polys tichum, we may now turn. 



There are three British species of Polystichum, illustrated as fully as the size of the 

 page permits in Figs. 75-77. The first of these, P. Lonchitis (L.) Roth, the Holly Fern, 

 is rare in the British Isles except on some of the richer Scottish mountains. It is usually a 

 plant of high altitudes save for a few localities, such as the hmestone ' Pavement ' areas 

 of Yorkshire. Once seen in the fully mature condition it cannot be confused with any- 

 thing else, though young plants of P. aculeatum are sometimes mistaken for it by those 

 unfamiliar with the true Holly Fern. Though rarely abundant in Britain it is both wide- 

 spread and often prolific in many other European countries, having a total range which 



* The importance of this proviso will probably become more obvious at a later stage in the book, 

 but it should perhaps be pointed out at once that completeness of a sample within the parameter chosen 

 (in this case the geographical limits of the flora of Britain) is as necessary as any other consideration to 

 its claim to be fairly representative. Any selection within the sample leading to deletion of certain ele- 

 ments for extraneous reasons such as horticultural or cytological convenience to the observer will 

 necessarily falsify the picture by over-simplification. 



The impossibility of obtaining truly random sampling of the world's vegetation in a botanic garden 

 is one of the many reasons for believing that a complete study of a local small flora will be far more 

 informative than the comparison of a greater number of miscellaneous species of unknown origin which 

 might happen to be available from horticultural sources. 



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