Population structure of Pacific Cordyline fruticosa (Laxmanniaceae) with implications for human settlement of Polynesia.

The Polynesian-introduced Cordyline fruticosa is used as a proxy for reconstructing human colonization patterns in Oceania. Because of its material, nutritional, medicinal, and religious importance, green-leaved C. fruticosa was transferred by Polynesian settlers to virtually every habitable Pacific island before European contact. Previous studies propose that green-leaved C. fruticosa is unable to reproduce sexually. To confirm sterility, crosses between fertile and putatively sterile forms were performed. To look for population structure in C. fruticosa that might confirm sterility as well as illustrate patterns of human migration, amplified fragment length polymorphism data were generated. Genotypic similarities were visualized using neighbor joining phenograms and analyses of molecular variance and principal components. The results from greenhouse crosses show that the Eastern Polynesian form is sterile; this finding is corroborated by a lack of genetic variability in Eastern Polynesian accessions. Sterile C. fruticosa appears to have been preferentially transferred throughout Eastern Polynesia; selection for the sterile form may be related to consumption of its rhizomes. Identification of a sterile form of C. fruticosa, possibly developed within Western Polynesia, may be significant to the systematics of Cordyline because it raises the possibility that the fertile form may actually be native to some Pacific islands.