Variation in Leptospermum trinervium (Myrtaceae): a problem species and the species problem

Abstract

Leptospermum trinervium is a variable species that has proved to be taxonomically puzzling because of interpopulation heterogeneity and sympatry of extreme forms. Variation within the species was initially investigated by phenetic analysis of adult morphology from herbarium specimens. Clustering analysis first suggested the existence of two major phenetic groups. Group definition was refined using discriminant function analysis by defining the most phenetically distinct groups. Ordination procedures (canonical variate analysis and non-metric multidimensional scaling) confirmed the absolute distinctness of these two phenetic groups. Seven locations were then studied in detail. Three of these locations contained sympatric populations of the two phenetic forms. Phenetic analysis of adult morphology using discriminant function analysis and univariate analyses supported the recognition of the two phenetic groups but also indicated a high degree of distinctness among all populations, and particularly between sympatric populations where no intermediates were found. Diagnostic differences were retained even when seeds from these populations were cultivated under standardised conditions, indicating a genetic basis to the morphological heterogeneity. Preliminary data on genetic structure from allozymes indicated that the sympatric populations were less similar to each other than they were to other phenetically similar populations elsewhere, suggesting a barrier to gene flow between these sympatric populations. These results suggest that the two phenetic groups should be recognised as distinct, but variable, species.