Origin of high-elevation Dendrochilum species (Orchidaceae) endemic to Mount Kinabalu, Sabah, Malaysia

Mount Kinabalu, (Sabah, Malaysia) is the youngest (ca. 1.5 million yrs old) and highest (4,095 in) mountain between the Himalayas and Irian Jaya, Indo nesia. Because of this combination of youth and isolation, considerable mys tery surrounds the origins of its high elevation endemics. We chose a group of high-elevation species from Dendrochilum subgen. Platyclinis sect. Eury brachium to begin an investigation of the origin(s) of endemicity on Mount Kinabalu. We tested biogeographic hypotheses that the Kinabalu endemics aro se from ancestors in: 1) the high mountains of Sumatra, 2) the high mountai ns of Mindanao, Philippines, and 3) lower elevations on Mount Kinabalu or e lsewhere in Borneo. Using phylogenetic patterns predicted by the three comp eting hypotheses, we evaluated which had the highest support in a likelihoo d framework. Based on analyses of ITS 1 and ITS 2 sequence variation in Den drochilum, we rejected hypotheses that the Kinabalu high-elevation endemics arose from ancestors in other high mountains of southeast Asia (Sumatra or the Philippines), and tentatively accepted their origin from lower elevati on ancestors in Borneo. The origin of high-elevation endemics from lower el evation Bornean ancestors appears to be a general mode of evolution for man y species on Mount Kinabalu.