Teucrium chamaedrys, also called wall germander, is a small woody shrub native to the Mediterranean region. Its name is derived from the Greek words meaning ‘ground oak’, since its tiny leaves resemble those of an oak tree. Teucrium species are prolific producers of diterpene skeletons and compounds, which afford them valuable properties widely co-opted in traditional and Western medicines. Specifically, Teucrium is well known for making clerodane-type diterpenoids that are produced from the backbone kolavanyl diphosphate. In order to begin to elucidate some of the complex biosynthetic pathways of these medicinal compounds, we identified and functionally characterized several kolavanyl diphosphate synthases from T. chamaedrys. Along the way, we discovered the genome of this species to be one of the largest genomes published from the Lamiaceae family, to which it belongs. This tetraploid, 3 Gbp genome is especially rich in diterpene synthase genes, with 74 putative sequences identified. The vast majority of these diterpene synthase genes belong to four genomic loci, representative of the four copies of the genome. Comparative genomics show that this cluster is mirrored in the closely related species, T. marum. Along with the presence of several cytochrome p450 sequences, this region is one of the largest biosynthetic gene clusters identified to date. Its remarkable chemistry and model tetraploidy make T. chamaedrys an interesting model for studying genomic evolution and adaptation in plants.