♦< 



THE GENUS DRTOPTERIS IN BRITAIN 

 is of importance first in showing that D. aemula fits well into the cytological scheme of 

 the genus Dryopteris outlined already by the Male Fern story. The exact identity of 

 chromosome number between D. aemula and the diploid species D. abbreviata is, how- 

 ever, also of interest in showing that this somewhat unusual prime number must be 

 far older than the Male Fern complex itself, and it will be found, indeed, to characterize 

 not only these species but also several other related genera as the next chapter will 

 show. 



A second somewhat isolated species is D. Villarsii (Bell.) 

 Woynar [D. rigida (Hoffm.) Underw.). This plant J^^ 



inhabits the deep cracks in the limestone pavement of SM 



parts of the northern Pennines, but elsewhere in Britain ^^ 



it seems to have been recorded only from one doubtful ^J|P 



station in north Wales. In Switzerland it occurs as an 

 alpine, and therefore its British station may be suspected O 



to be that of a glacial relict. In Great Britain D. Villarsii ^ A 



is a tetraploid species having w = 82 (Fig. 53^). As in ^ jj^ 



D. Filix-mas quadrivalents are absent. A somewhat un- ^^SJ ^^ 



expected observation made as a result of a personal ^^^M 



visit to Switzerland in the summer of 1947 is, however, ^Ci^ ^KJ^ 



that the species in that country is diploid. Fixations ^^iJ^ ^ 



were taken both in the alpine garden of Pont-de-Nant sur • ^ 



Bex and on the wild plants in their natural habitat some 90 



kilometres away. The number is unquestionably half 



that of British material. This observation was obtained W^ 



too late to be given more than a passing mention before D.sejnula n = 4i 

 this manuscript is completed for the press, but it raises Fig. 51. Explanatory diagram 

 some very interesting problems concerning the past to Fig. 53a. x 1500. 



history and nature of D. Villarsii in Britain, which will 

 perhaps be further pursued elsewhere. 



The next group of species can best be treated together. They are the species complex 

 once united under the now obsolete name of ' Nephr odium spinulosum\'' but long since 

 resolved, by the common consent of taxonomists, into three good species and the 

 hybrids between them. The three good species are D. cristata (L.) A. Gray, D. spinulosa 

 (Miill.) Watt and D. dilatata (Hoffm.) A. Gray. They differ from each other in morpho- 

 logy, habitat and frequency of occurrence. D. cristata, the rarest of the three, is a 

 plant of very wet bogs, so rare as to be in danger of extinction in this country, no doubt 

 in part owing to drainage. It was formerly recorded from a few isolated stations in a 

 number of counties scattered from Dorset to the Glasgow area, but it appears to have 

 died out in most of these except Norfolk. It has, however, recently been discovered in 

 Surrey (Payne, 1939) and is still to be found near Glasgow. D. spinulosa, in contrast, 

 is found in most parts of the British Isles and is often abundant, though it is limited 



* Ignorance of the biology and taxonomy of this group has led some recent writers on evolution, 

 notably Huxley (1942), to some very erroneous conclusions. 



MFC 65 5 



