Taxonomic realignment of Senecio glaucophyllus (Asteraceae; Senecioneae) necessitates a new name for a widespread New Zealand species

Abstract

ABSTRACT As presently delimited, the endemic New Zealand species Senecio glaucophyllus Cheeseman shows considerable morphological and ecological diversity. Two morphologically similar forms associated with this taxon are found in northwest Nelson (South Island), of which one is often filed in herbaria as S. glaucophyllus subsp. glaucophyllus. The other form has been informally recognised as S. aff. glaucophyllus. The present study aimed to determine if S. aff. glaucophyllus merits taxonomic recognition by assessing if it is morphologically and genetically distinct from S. glaucophyllus subsp. glaucophyllus and, if so, to identify its diagnostic morphological characters. The results of Principal Coordinate Analyses of a morphometric data set and phylogenetic studies of an ITS DNA sequence data set show that the two taxa are morphologically and genetically distinct and only distantly related to each other. Random Forest analyses resulted in the discovery of several morphological characters that can be used to distinguish the taxa. The inclusion of data of type specimens of S. glaucophyllus in the PCoAs showed that specimens of S. aff. glaucophyllus are conspecific with S. glaucophyllus whereas most of S. glaucophyllus in its current delimitation belong to a taxon that is unnamed at the species level. We here provide a new name at species rank for this taxon: Senecio matatini. This taxonomic realignment reinstates Cheeseman’s original concept of S. glaucophyllus as a species that is restricted to northwest Nelson. Senecio matatini has a much wider distribution and is found throughout much of the South Island and the southern and central parts of the North Island. Because our results indicate that S. glaucophyllus subsp. basinudus, S. glaucophyllus subsp. discoideus, and S. glaucophyllus subsp. toa are currently best considered as subspecies of S. matatini, new combinations for these three taxa are also provided. In addition, we lectotypify the name Senecio lautus var. montanus Cheeseman.