Article Genetic Structure of the Tropical Tree Eusideroxylon zwageri in Indonesia Revealed by Chloroplast DNA Phylogeography I.L.G. Nurtjahjaningsih 1, * ,† , Sukartiningsih 2,† , Hiroyuki Kurokochi 3 , Yoko Saito 4 and Yuji Ide 4 1 Center for Forest Biotechnology and Tree Improvement, Jalan Palagan Tentara Pelajar Km. 15 Purwobinangun, Pakem Sleman, Yogyakarta 55582, Indonesia 2 Faculty of Forestry, Mulawarman University, Campus Gunung Kelua, Jl. Ki Hajar Dewantara, Samarinda, East Kalimantan 75119, Indonesia; sukartiningsih1@gmail.com 3 Laboratory of Forest Molecular Ecology, Asian Natural Environmental Science Center, University of Tokyo, 1-1-8 Midori-cho, Nishitokyo, Tokyo 188-0002, Japan; kurokochi@anesc.u-tokyo.ac.jp or h.kurokochi@gmail.com 4 Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo 113-8657, Japan; yoko@es.a.u-tokyo.ac.jp (Y.S.); ide@es.a.u-tokyo.ac.jp (Y.I.) * Correspondence: iluh_nc@yahoo.com; Tel.: +62-8154-8807-444 † Those authors contributed equally to this paper. Academic Editors: Om P. Rajora and Timothy A. Martin Received: 10 April 2017; Accepted: 22 June 2017; Published: 29 June 2017 Abstract: Eusideroxylon zwageri is a large tropical rainforest tree native to Indonesia, Malaysia, the Philippines, and Brunei. Because of its high economic value, illegal logging and overexploitation is threatening this species in several locations in Indonesia. In this study, in order to conserve genetic resources, we investigated the genetic structure of E. zwageri in Indonesia using chloroplast DNA sequencing. Eusideroxylon zwageri samples were collected from the Kalimantan (56 trees from seven populations) and Sumatra (16 trees from two populations) islands of Indonesia. Approximately 3137 bp of chloroplast DNA was sequenced for each tree. Twenty-one haplotypes were identified, of which six haplotypes were detected from two or three populations, whereas the other 15 haplotypes were detected from one population each. For each population, one to six haplotypes were detected, and phylogenetically closer haplotypes were detected within the same population. Although the haplotypes were roughly divided into two groups, geographically-close populations did not always have phylogenetically-close haplotypes. Our results suggest that in Indonesia, E. zwageri showed a high genetic diversity at the chloroplast DNA level, and populations within a population were derived from similar maternal lineages. Therefore, transplantation within a population may be a feasible option for E. zwageri conservation. However, transplantation among different populations should be conducted with careful consideration, because geographic distances are not always related to phylogenetic distances in E. zwageri. Keywords: Borneo ironwood; chloroplast DNA sequencing; chloroplast haplotype; Kalimantan; Sumatra 1. Introduction Eusideroxylon zwageri T.et B (Borneo ironwood) is a large tropical rainforest tree native to Indonesia, Malaysia, the Philippines, and Brunei. In Indonesia, this species is naturally distributed in the Kalimantan, Sumatra, and Bangka-Belitung islands. Owing to its strong and water-resistant wood, it has high economic value in the construction of bridges, ships, boats, and houses. However, this leads to illegal logging and overexploitation, which is threatening this species in several Forests 2017, 8, 229; doi:10.3390/f8070229 www.mdpi.com/journal/forests