Morphological and genetic diversity in the New Zealand fern Polystichum vestitum (Dryopteridaceae), with special reference to the Chatham Islands

Some plants of Polystichum from the Chatham Islands exhibit morphological character states unknown from the North and South Islands of New Zealand. Several workers have suggested that these plants should be given taxonomic recognition. However, analyses of morphological and molecular (AFLP-DNA fingerprinting) data provide no strong evidence that these morphologically divergent Chatham Islands plants constitute an evolutionary lineage separate from the remainder of P. vestitum. We consequently suggest the retention of P. vestitum as a single, albeit morphologically variable, taxonomic species, with no subspecies. Varietal-level classification of the morphological variation is discussed, but its implementation is not recommended Morphological similarities between some plants of P. vestitum from the Chatham Islands and some from the islands in the subantarctic and around Stewart Island are not reflected by a close genetic relationship.