The taxonomic treatment of polymorphic variation

Abstract

385 The argument is advanced that polymorphic variation in many characters, e.g. flower-colour, hairiness, is common in British (and European) plants; that the extent of the polymorphism is often geographically variable; that it may be of evolutionary significance; and that it is sometimes worthy of taxonomic recognition, under the category of forma. Two new forms and a new varietal combination are recognised within Viola rivinialla Reichenb. The treatment of variation by taxonomists is not always consistent. For example, in an apomictic species such as Rubus fruticosus L. a single deviant individual in a population may be described as a new species, though it may be found only in a single locality and may possibly not be true-breeding. On the other hand, the white- and red-flowered variants of a species such as Cirsium palustre (L.) Scop. may not receive taxonomic recognition of any kind, even though the poly-morphic variation which they show may be widespread and of considerable biological significance.