The New Zealand karaka tree, Corynocarpus laevigatus J.R. & G.Forst., is shown to be gynodioecious. Flowers on female plants have large but empty anthers and many set fruit. Flowers on male plants produce pollen and each has a fully developed ovule. On most male plants, a low proportion of flowers set fruit. Inflorescences and flowers on male and female trees are similar in overall appearance, except that the flower parts on males are larger and flowers open more widely. Even the gynoecia on male plants are larger in most respects. We also report that although trees retain their gender, their intensity of fruiting varies from year to year. Some observations indicate that other species of Corynocarpus in Australia and the south-western Pacific might also be gender dimorphic.