Genetic variation and structure of remnant stands of pohutukawa (Metrosideros excelsa, Myrtaceae)

Genetic variation and interpopulation structure were assessed in 20 populat ions of the New Zealand coastal tree Metrosideros excelsa (pohutukawa) usin g allozyme markers. Average levels of polymorphism (P = 58%) and allelic ri chness (N-a = 1.69) were typical of long-lived trees and higher than has be en previously observed for other New Zealand tree species, which have gener ally been found to be genetically depauperate. Observed heterozygosity was low (mean H-o = 0.12) and consistently less than expected under Hardy-Weinb erg equilibrium (F-is = 0.26), suggesting significant inbreeding. Interpopu lation genetic differentiation was moderate (F-st = 0.20, mean D = 0.053) a nd this was correlated with low interpopulation gene flow estimates (Nm = 1 .15). These results suggest that revegetation programmes should source seed locally and avoid taking material from small populations in which selfed s eed may make up a significant portion of the seed crop.