Ceylon oak (Schleichera oleosa (Lour.) Oken), belonging to Sapindaceae family, is a widely used plant for its medicinal properties. Currently, few studies have been conducted on Ceylon oak’s genetic background and its relationship with other closely related plants in Thailand. Therefore, this study focused on the analysis of nucleotide sequences to understand the genetic diversity and relationship of Ceylon oak with longan and lychee. The nucleotide sequencing of six loci, namely ITS2, matK, rbcL, trnH-psbA, trnL-i and trnL-trnF was analyzed in five Ceylon oak samples collected from various locations in Thailand and then were additionally aligned with nucleotide sequences of 36 longan samples and 2 lychee samples (7 species) (GenBank accession nos. KY174077–KY174314). The sequencing results were then used to construct a phylogenetic tree using the maximum likelihood criteria. Multiple sequence alignment revealed the highest InDel polymorphism of trnH-psbA fragment which can be developed as a DNA molecular marker in the identification of Ceylon oak. Interestingly, the K2P pairwise distance analysis revealed a high degree of genetic variation between Ceylon oak, longan and lychee samples and the combination of either matK and trnH-psbA or matK and ITS2 provided the most potential candidate DNA barcoding region for discrimination of Ceylon oak from longan and lychee. The phylogenetic tree showed that Ceylon oak is completely different from longan and lychee. This is the first report of phylogenetic information among Ceylon oak, longan and lychee in Thailand which might be used to assist Ceylon oak conservation and breeding program in the future.

锡兰橡树（Schleichera oleosa (Lour.) Oken）属于无患子科，因其药用特性而成为一种广泛使用的植物。目前，关于锡兰橡树的遗传背景及其与泰国其他密切相关植物的关系的研究很少。因此，本研究重点对核苷酸序列进行分析，以了解锡兰栎的遗传多样性以及与龙眼和荔枝的关系。ITS2、 matK、rbcL、trnH-psbA、trnL-i和trnL-trnF 6 个位点的核苷酸测序对从泰国不同地点收集的 5 个锡兰橡木样品进行了分析，然后与 36 个龙眼样品和 2 个荔枝样品（7 个物种）的核苷酸序列进行了比对（GenBank 登录号 KY174077-KY174314）。然后使用测序结果使用最大似然标准构建系统发育树。多重序列比对揭示了trnH-psbA片段最高的InDel多态性，该片段可作为锡兰栎鉴定中的DNA分子标记。有趣的是，K2P 成对距离分析揭示了锡兰橡树、龙眼和荔枝样品之间以及matK和trnH-psbA或matK组合之间存在高度遗传变异。ITS2为锡兰橡树与龙眼、荔枝的区分提供了最有潜力的候选DNA条形码区域。系统发育树显示锡兰橡树与龙眼和荔枝完全不同。这是泰国第一份关于锡兰橡树、龙眼和荔枝的系统发育信息的报告，未来可能用于协助锡兰橡树的保护和育种计划。