Somatic mutations are thought to be fundamentally important to the ecology and evolution of plants, but we know very little about them because they are rare and difficult to detect. We have developed methods to reliably measure the genome-wide accumulation of somatic mutations in individual plants. By applying them to individual eucalypts of large stature, we are able to measure both the rate and spectrum of new mutations accumulating within individuals. In addition, we can pinpoint mutations of potential interest in understanding herbivore-resistant phenotypic mosaics. Our results have some interesting implications for plant ecology, evolution, and development.