Format: ORAL

Ickert-Bond, Stefanie M.1, Polezhaeva, Maria A.2, Oliver, Margaret G.3

1 UA Museum of the North Herbarium and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-6960, USA 2 Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Science, Ekaterinburg, 8 Marts Str., 202, 620144, Russia 3 University of Tennessee Herbarium, The University of Tennessee – Knoxville, Knoxville, TN 37996-2800, USA

Therorhodion is a small genus including three species T. redowskianum with an Asian-restricted range and two amphiberingian taxa T. camtschaticum and T. glandulosum. The Kamchatka rhododendron (Therorhodion camtschaticum s.l.) is a small cold-resistant arcto-alpine shrub species with a controversial intraspecific taxonomy and a wide distribution range covering northern Eurasia and North America within Beringia. Russian taxonomists recognize one species with two subspecies, whereas two distinct species are recognized in North America following a broader species concept. We set out to unravel the taxonomic relationships within Therorhodion and the likely dispersal route/s of T. camtschaticum and T. glandulosum. First, we look at the overall phylogeny and recover strong molecular support for Therorhodion as the sister clade to Rhododendron, and within Therorhodion three strongly supported monophyletic clades representing three species are inferred. Next, we assess the level and distribution of diversity in the two closely related amphiberingian species within the native species range. The degree of differentiation we found is consistent with the species rather than subspecies status of the taxa studied. Two genetic lineages reflect the migration pathways of species from western Beringia to eastern Beringia. A northern pathway for T. glandulosum from northern East Asia (Okhotsk seashore, the Kolyma region, Chukotka, central and northern Kamchatka) to the Seward Peninsula in northern Alaska. A southern pathway for T. camtschaticum from the southern part of western Beringia (the Sikhote-Alin ridge, Sakhalin Island, the Kuril Islands, and southern Kamchatka) to the Aleutian Islands and the seashore of southeast Alaska. We inferred a divergence of Therorhodion from Rhododendron in the late Paleocene with the Asian-restricted T. redowskianum diverging during the middle Miocene, supporting an Asian origin for the genus. Demographic analysis using nSSR data inferred a divergence time between T. camtschaticum and T. glandulosum in the Pleistocene at 1.52 Ma.