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Molecular phylogeny and adaptive radiation of the endemic Hawaiian Plantago species (Plantaginaceae)¹

² Department of Botany, University of Hawai‘i, 3190 Maile Way, Honolulu, Hawai‘i 96822 USA ³ Department of Tropical Plant and Soil Sciences, University of Hawai‘i, 3190 Maile Way, Honolulu, Hawai‘i 96822 USA

ABSTRACT

Insular oceanic islands provide excellent opportunities for the study of evolutionary processes and adaptive radiation. The Hawaiian Plantago radiation comprises six endemic taxa showing considerable inter- and intraspecific morphological and ecological diversity. The rDNA internal (ITS) and external (ETS) transcribed spacers and two recently described chloroplast spacers, ndhF-rpl32 and rpl32-trnL, were sequenced to study phylogenetic relationships within this morphologically complex group. Phylogenetic analysis provided strong evidence for the monophyly of Hawaiian Plantago, suggesting that the lineage arose from a single long-distance dispersal event. Inconsistencies between nuclear and chloroplast phylogenies suggest a history of hybridization. The basal, unresolved dichotomy of the combined phylogeny is consistent with rapid phenotypic diversification of the major lineages early in the history of this group. Speciation has largely occurred allopatrically, with divergence a result of intraisland ecological shifts between bog and woodland habitats and interisland dispersal events. Most interisland colonizations were from older to younger islands with initial colonization of Kaua‘i. In our analysis, P. pachyphylla is paraphyletic and taxonomic separation of the distinct morphotypes of this species appears justified. Furthermore, the apparent hybrid ancestry and unique morphology and habitat of the endangered P. princeps var. longibracteata support its recognition at the specific rank.

Key Words: adaptive radiation • biogeography • Hawaiian Islands • hybridization • ndhF-rpl32 • phylogeny • Plantaginaceae • Plantago • rpl32-trnL

Received for publication 9 April 2008. Accepted for publication 19 July 2008.

FOOTNOTES

¹ The authors thank M. Bruegmann, V. Caraway, P. Garnock-Jones, R. Hoggard, D. Lorence, T. Motley, H. Oppenheimer, and M. Schultz for kindly sending specimens; and A. Bakutis, K. Bio, K. Dunbar, M. LeGrande, A. Medeiros, H. Oppenheimer, S. Perlman, N. Tangalin, J. TenBruggencate, and the O‘ahu Army Natural Resources Program for assistance in the field. We also thank the Hawai‘i State Department of Forestry and Wildlife, U. S. Fish and Wildlife Service, Haleakala National Park, Hawai‘i Volcanoes National Park, The Nature Conservancy of Hawai‘i, and Maui Land and Pineapple Co. for the access and permits required to do this work. The following herbaria generously provided material for this study: ALTA, BISH, HAW, MOT, PTBG, OSC, NY, UBC and WELTU. Helpful comments on this manuscript were provided by G. Carr, S. Conant, D. Drake, Z. Forsman, D. Lorence, M. Nepokroeff, and T. Ranker. This work was funded by an Environmental Protection Agency Graduate Fellowship and a University of Hawai‘i ‘iwi Ake Akamai Doctoral Completion Fellowship awarded to S.D-C.

⁴ Author for correspondence (e-mail: sdunbar{at}hawaii.edu)