THE ROLE OF TAXIMETRICS IN ANGIOSPERM TAXONOMY I. EMPIRICAL COMPARISONS OF METHODS USING CROTALARIA L.

SUMMARY Two hundred and seventy‐three African species of Crotalaria L. (Leguminosae) were subjected to three taximetric procedures: single‐link clustering, with subgraph representation; principal co‐ordinate analysis; and median clustering. The classifications suggested by these methods were compared with each other, compared with a contemporary orthodox classification by Polhill and checked against the original plant material to see if the groupings were recognizable notwithstanding any similarity with Polhill's classification. Above the species level Crotalaria presents classification problems in size and complexity not uncommon for the angiopersms. The results of single‐link clustering suggest a classification close to Polhill's. In one case, where selected characters had been used, much of the correspondence is exact and of the few discrepancies some reveal possible improvements to the classification and others were caused by external factors. The principal co‐ordinate analysis results are difficult to interpret, suggest some unrecognizable groupings and only vaguely resemble Polhill's arrangement. The median clustering results suggest a tidy‐looking classification which, on investigation, proves largely spurious. The single‐link and principal co‐ordinate analysis were used to process two different sets of data. One set consisted of data for characters chosen mainly from the other set, selected for high intercorrelations using the information contribution measure. For both methods data for the selected character set gave more useful results. These findings favour the use of single‐link clustering for classifying angiosperms above the species level. They are a variance with the conclusions of some earlier empirical comparisons using angiosperms, but lend support to a number of theoretical arguments for preferring the single‐link procedure.