Chemical diversity and phylogenetic insights into Hawaiian ʻākia ( Wikstroemia ) species used in traditional fishing practices

Societal Impact Statement Traditional fishing with plant‐based piscicides is a global practice in decline, facing increasing restrictions. We investigated the chemical diversity of endemic Wikstroemia species historically used to stun or poison fish in Hawaiʻi. Using 1‐H‐NMR, principal component analysis, targeted HPLC, and target‐capture sequencing, we characterized compounds and built the first Hawaiian Wikstroemia molecular phylogeny. Chemical variation reflected plant part and collection location, revealed new compound records, and suggested shared ancestral chemistry across species, without a direct link between genetics and chemical profiles. Broadly, findings can support policy‐ and practice‐informed conservation and sustainable, culturally appropriate fishing. Summary Traditional fishing methods in Hawai‘i use native and introduced plants to stun or poison fish, a global practice that is disappearing and increasingly restricted. We investigate the chemical diversity within ʻĀkia, endemic Hawaiian Wikstroemia species ( W. furcata , Wikstroemia monticola , Wikstroemia oahuensis , and Wikstroemia uva‐ursi ) historically used as piscicides. Forty‐five samples from Kaua‘i and Maui were analyzed using 1 H‐nuclear magnetic resonance (NMR) spectroscopy and principal component analysis (PCA) to explore chemical diversity, and targeted High‐Performance‐Liquid‐Chromatography (HPLC) to identify major compounds. Target Capture sequencing using the universal Angiosperms 353 probe set was conducted to build the first molecular phylogeny of Hawaiian Wikstroemia . Chemical variation was primarily associated with plant parts and collection location. Rutarensin and isoquercetin were identified in W. uva‐ursi for the first time. Daphnoretin, the aglycone of rutarensin, has previously been isolated from other piscicidal plants, but its potential piscicidal activity has not yet been demonstrated. Phylogenetic analysis revealed a monophyletic group of W. uva‐ursi and three distinct clades of Hawaiian Wikstroemia corresponding to three of the major high island complexes. The widespread species complex of W. oahuensis was highly polyphyletic. No direct correlation between genetic relationships and chemical diversity was found. Instead, chemical compounds are a shared ancestral characteristic among all extant Hawaiian Wikstroemia . The chemical similarities suggest that different Hawaiian Wikstroemia species could potentially be used interchangeably for fishing, though variation between plant parts remains important. The findings obtained may support communities in the continued development of sustainable, culturally appropriate practices.