In Mexico, Magnolia species of the section Macrophylla have been segregated based on phenotypic characteristics. However, the wide environmental variation throughout their distribution area in the eastern region of the country could be the main cause of the high degree of morphological variation among the taxa of this section. Therefore, it is necessary to carry out studies at the genetic level to confirm the taxonomic identity of these species. In the present study, the diversity and genetic structure of the populations of Magnolia rzedowskiana and M. zotictla were estimated using simple sequence repeat markers. We evaluated whether the taxonomic delimitation as independent species is consistent with their degree of genetic differentiation, comparing three regions of chloroplast DNA: trnH-psbA, ORF350, and rpl32-trnL. The DNA was obtained from four populations of the two species, which are distributed in the states of Hidalgo, Querétaro and San Luis Potosí. The populations presented intermediate–high genetic diversity (He = 0.52–0.60), limited gene flow (Nm = 0.62) and high genetic differentiation (Fst = 0.288), which may be related to their low density and strong geographic isolation, caused by the high degree of fragmentation of their habitat. The phylogenetic analysis and the genetic differentiation values indicate that each of the populations of the two Magnolia species analyzed behaves as an independent evolutionary unit, so the taxonomic delimitation of the three M. rzedowskiana populations must be reconsidered. The results obtained could be very useful for implementing management and conservation strategies for these populations in the short term.

中文翻译：

---

墨西哥东部特有的两种木兰物种的结构、多样性和遗传界定

在墨西哥，玉兰属该科的物种大叶植物已根据表型特征进行分离。然而，该国东部地区整个分布区的巨大环境变化可能是该地区类群形态高度变异的主要原因。因此，有必要在遗传水平上进行研究，以确认这些物种的分类学身份。在本研究中，种群的多样性和遗传结构玉兰和斑马鱼使用简单的序列重复标记进行估计。我们通过比较叶绿体 DNA 的三个区域：trnH-psbA、ORF350 和 rpl32-trnL，评估了作为独立物种的分类学界定是否与其遗传分化程度一致。 DNA 是从这两个物种的四个种群中获得的，这些种群分布在伊达尔戈州、克雷塔罗州和圣路易斯波托西州。种群呈现中高遗传多样性（He = 0.52–0.60）、有限的基因流（Nm = 0.62）和高遗传分化（Fst = 0.288），这可能与其低密度和强烈的地理隔离有关。它们的栖息地高度破碎。系统发育分析和遗传分化值表明这两个群体的每个群体玉兰属所分析的物种表现为一个独立的进化单位，因此这三个物种的分类学界限热多夫斯基纳必须重新考虑人口。获得的结果对于在短期内实施这些种群的管理和保护策略非常有用。