AUTHOR=Tian Xinmin , Wang Qiuyan , Zhou Yongfeng 

TITLE=Euphorbia Section Hainanensis (Euphorbiaceae), a New Section Endemic to the Hainan Island of China From Biogeographical, Karyological, and Phenotypical Evidence

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00660

DOI=10.3389/fpls.2018.00660

ISSN=1664-462X

ABSTRACT=<p><italic>Euphorbia hainanensis</italic> is an endangered species endemic to the tropical Hainan Island in southern China and of historical importance for Chinese medicine. It is currently the only unplaced species of the genus <italic>Euphorbia</italic> (Euphorbiaceae) due to its isolated island distribution and debated placement by a previous molecular phylogenetic study. We sequenced nuclear ITS and chloroplast <italic>rbcL</italic> and <italic>ndhF</italic> for newly collected accessions of <italic>E. hainanensis</italic> and additional <italic>Euphorbia</italic> species found in Hainan, and analyzed the sequences in the context of the entire genus together with published data. All gene regions highly supported that <italic>E. hainanensis</italic> occupied an isolated phylogenetic position, showing no close affinity with any known <italic>Euphorbia</italic> sections suggesting it was a new section. ITS placed <italic>E. hainanensis</italic> sister to sect. <italic>Crossadenia</italic> (subgenus <italic>Chamaesyce</italic>) from Brazil with an estimated divergence time of 9.3-30.6 Mya while the chloroplast markers placed <italic>E. hainanensis</italic> at a position sister to the entire New World clade of <italic>Euphorbia</italic> subgenus <italic>Chamaesyce</italic>. In addition, our karyological results suggested a close affinity between <italic>E. hainanensis</italic> and the New World species of <italic>Euphorbia</italic> subg. <italic>Chamaesyce</italic>, with which shared the same chromosome number 2n = 28 and basic chromosome number x = 7. Phenotypically, <italic>E. hainanensis</italic> is unique with no close resemblance to other species in <italic>Euphorbia</italic> subg. <italic>Chamaesyce</italic>. Based on its isolated biogeographical, karyological, and phenotypical position, we propose a new section <italic>E</italic>. subgenus <italic>Chamaesyce</italic> section <italic>Hainanensis</italic> that might origin from long distance dispersal events because collective evidences showed a close affinity between the species from the Old World with those from the New World.</p>