Phylogenetic and biogeographic relationships of cheirodendron nutt. Ex. Seeman (Araliaceae)

Abstract

Cheirodendron is a genus of six arboreal species in the family Araliaceae, distributed in the Hawaiian and Marquesas Islands. Previous and current revisions were assessed using morphological characteristics, resulting in the present taxonomy that consists of five species and two subspecies in Hawaii and one species in the Marquesas. For the first time, molecular phylogenetic analyses were carried out to determine species and biogeographic relationships using sequences from the internal and external transcribed spacer regions of nuclear ribosomal DNA, and the ndhF-rpl32 chloroplast spacer region. The results suggest that Cheirodendron is a monophyletic group with Marquesan species C. bastardianum sister to the Hawaiian Cheirodendron. Within the Hawaiian Cheirodendron, a clade of non-Kauai taxa was well-supported and a clade of Kauai taxa was weakly supported. However, species relationships within the Hawaiian clades were unresolved. Phylogenetic differences among subspecies suggest the recognition of two previously-recognized species, C. helleri Sherff and C. kauaiense Kraj. Results suggest two possible biogeographic patterns of Cheirodendron in the Pacific: (1) a stepping stone pattern of dispersal from New Zealand to Marquesas, and Marquesas to Hawaii or (2) a simultaneous colonization of both Hawaii and Marquesas. Understanding species relationships and the biogeography of Cheirodendron adds to our knowledge of the evolution and speciation of Pacific island groups. Long distance dispersal, along with in situ speciation on island archipelagos provides interesting evolutionary and biogeographic patterns to be discussed.