The genus Polyscias, part of the Araliaceae family, is known for its significant ornamental and medicinal value, as well as its rich variety of metabolites. These plants are primarily found in tropical regions, particularly in Southeast Asia and the Pacific islands. The diverse geographical environments have led to the emergence of many unique and endangered species, although there is limited genomic information available about them. In this study, we generated high-quality reference genomes for three endangered species: two that are endemic to Hawai'i, Polyscias cf. bisattenuata and Polyscias lallanii, and one more widespread species, Polyscias macgillivrayi. We identified a total of 51,083, 60,881, and 29,060 genes in these three species, respectively. Whole-genome duplication analysis indicated that all three species underwent a common duplication event. By examining the phylogenetic and structural characteristics of the terpene synthase gene family in these species and closely related species, we identified several gene clusters that play crucial roles in metabolite synthesis. A variety of mono- and sesquiterpenoids were detected, with several of these compounds having been validated in previous studies. Our findings provide a foundation for further genetic and biochemical investigations of Polyscias, which may aid in the conservation of these endangered species.