A numerical study of the variation in the New Zealand erechtites arguta-scaberula complex (Senecioneae-Compositae)

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Abstract
Thirteen numerical attributes taken from phyllaries, calycule, peduncle and florets were recorded for a sample of 65 specimens representing the New Zealand Erechtites arguta (syn. Senecio glomeratus)—Erechtites scaberula (syn. Senecio hispidulus) complex. The comparative data were subjected to computer analyses using Squared Euclidean Distance (D2 ) and Gower's Index as similarity statistics in conjunction with Nearest. Median and Furthest neighbour and Centroid (C) sorting strategies during the commissioning of ASSORT, a package of interrelated Algol procedures. The resulting agglomerative polythetic classifications conform to a basic structure exemplified by the D2 -C result. Two major groups consisting of four and five subgroups respectively were detected from the computed hierarchy. Thirteen additional characters taken from stem, leaf, involucre, corolla and achenes together with geographical data were used to show that the two major groups and only one subgroup exhibit taxonomic properties. Reference to nomenclatural type material and other critical specimens for the complex confirm the presence in New Zealand of Senecio glomeratus and S. hispidulus varieties hispidulus and scaberulus. Our results do not sustain the suggestion that S. hispidulus and S. glomeratus hybridise freely over much of their largely overlapping range. However, the analyses expose an assemblage intermediate in floral details between S. hispidulus variety scaberulus and variety hispidulus for which an hybrid origin is postulated. S. glomeratus in New Zealand shows partial segregation into two elements. In numerical taxonomic terms the study demonstrates the value of the ASSORT package as applied to a standard taxonomic problem. Furthermore, the constituent procedures would seem to provide a realistic framework in which to carry out the much needed experimental research into taxonomic theory.