W Harris; RE Beever
Observations were made on the size, shape, and colour of leaves of 5- to 6-year-old trees of Cordyline australis (cabbage tree, ti kouka) raised from seed of 28 wild populations from a 12° latitudinal range in New Zealand and grown under uniform garden conditions at Lincoln (43°38′S, 172°43′E). Overall, mean population linear leaf dimensions increased, leaves became broader, and petioles were less defined the further south the population origin. These genotypic patterns were correlated with matching leaf phenotypic characteristics of trees at their source locations. Latitudinally related clines of variation were also shown for leaf colour states and states defining transverse curvature of leaf blades. Blade thickness, purple leaf-base coloration, and midrib distinctiveness showed regional foci of variation. Character distribution patterns indicate centres of variation in northern North Island and northern South Island. The variations of the leaf character states are discussed in relation to adaptation to irradiance and water availability. It is concluded that the variation observed is adequately described genecologically as predominantly continuous and clinal along ecological gradients, and regional discontinuities in the occurrence of character states do not merit taxonomic categorisation. The study supports in situ conservation of genetically distinct C. australis populations across the species range and emphasises the importance of using locally sourced seed where the species is planted to restore native plant communities.