Dubautia carrii and D. hanaulaensis, New Species of the Hawaiian Silversword Alliance (Compositae, Madiinae) from Moloka‘i and Maui

Dubautia carrii B. G. Baldwin & Friar and D. hanaulaensis B. G. Baldwin are new species in Dubautia Gaudich. sect. Railliardia (Gaudich.) G. D. Carr (Compositae, Madiinae) of the Hawaiian silversword alliance that were previously treated within the circumscription of D. linearis (Gaudich.) D. D. Keck subsp. opposita (Sherff) G. D. Carr. The two species are allopatric, with D. carrii in mesic to wet shrubland and forest on eastern Moloka‘i and D. hanaulaensis in mesic shrubland and forest on southern West Maui. Although closely resembling D. linearis subsp. linearis and D. linearis subsp. hillebrandii (H. Mann) G. D. Carr in habit and capitulescence characteristics, D. carrii and D. hanaulaensis differ from both subspecies of D. linearis in the sense adopted here by having consistently opposite (rather than variable) phyllotaxy and toothed (rather than entire) leaf apices, and by occurring in mesic or wet (rather than mostly dry) habitats. Dubautia carrii and D. hanaulaensis are highly similar morphologically; they commonly differ from one another in stature, stem vestiture, leaf shape, capitulescence size, and receptacular-bract glandulosity. Molecular phylogenetic data indicate that D. carrii is most closely related to the East Maui endemic species of Dubautia sect. Railliardia (i.e., D. menziesii (A. Gray) D. D. Keck, D. platyphylla (A. Gray) D. D. Keck, D. reticulata (Sherff) D. D. Keck, and D. waianapanapaensis G. D. Carr), and D. hanaulaensis represents an early-diverging lineage within the Maui Nui–Hawai‘i (Big Island) clade of Dubautia sect. Railliardia. High similarity of D. carrii and D. hanaulaensis in morphology and ecology may reflect retained ancestral or plesiomorphic states shared with the common ancestor of the Maui Nui–Hawai‘i clade of Dubautia sect. Railliardia, a lineage otherwise known for exceptional adaptive radiation.