Wang Ai-Hua, Sun Ye, Schneider Harald, Zhai Jun-Wen, Liu Dong-Ming, Zhou Jin-Song, Xing Fu-Wu, Chen Hong-Feng, Wang Fa-Guo
Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
BMC Plant Biol. 2015 Feb 5;15:36. doi: 10.1186/s12870-014-0361-9.
There are different opinions about the relationship of two disjunctively distributed varieties Adiantum reniforme L. var. sinense Y.X.Lin and Adiantum reniforme L. Adiantum reniforme var. sinense is an endangered fern only distributed in a narrowed region of Chongqing city in China, while Adiantum reniforme var. reniforme just distributed in Canary Islands and Madeira off the north-western African coast. To verify the relationship of these two taxa, relative phylogenetic analyses, karyotype analyses, microscopic spore observations and morphological studies were performed in this study. Besides, divergence time between A. reniforme var. sinense and A. reniforme var. reniforme was estimated using GTR model according to a phylogeny tree constructed with the three cpDNA markers atpA, atpB, and rbcL.
Phylogenetic results and divergence time analyses--all individuals of A. reniforme var. sinense from 4 different populations (representing all biogeographic distributions) were clustered into one clade and all individuals of A. reniforme var. reniforme from 7 different populations (all biogeographic distributions are included) were clustered into another clade. The divergence between A. reniforme var. reniforme and A. reniforme var. sinense was estimated to be 4.94 (2.26-8.66) Myr. Based on karyotype analyses, A. reniforme var. reniforme was deduced to be hexaploidy with 2n = 180, X = 30, while A. reniforme var. sinense was known as tetraploidy. Microscopic spore observations suggested that surface ornamentation of A. reniforme var. reniforme is psilate, but that of A. reniforme var. sinense is rugate. Leaf blades of A. reniforme var. sinense are membranous and reniform and with several obvious concentric rings, and leaves of A. reniforme var. reniforme are pachyphyllous and coriaceous and are much rounder and similar to palm.
Adiantum reniforme var. sinense is an independent species rather than the variety of Adiantum reniforme var. reniforme. As a result, we approve Adiantum nelumboides X. C. Zhang, nom. & stat. nov. as a legal name instead of the former Adiantum reniforme var. sinense. China was determined to be the most probable evolution centre based on the results of phylogenetic analyses, divergence estimation, relative palaeogeography and palaeoclimate materials.
对于间断分布的两个变种——肾叶铁线蕨中华变种（Adiantum reniforme L. var. sinense Y.X.Lin）和肾叶铁线蕨（Adiantum reniforme L.）之间的关系存在不同观点。肾叶铁线蕨中华变种是一种濒危蕨类植物，仅分布于中国重庆市的一个狭窄区域，而肾叶铁线蕨原变种仅分布于非洲西北海岸外的加那利群岛和马德拉群岛。为了验证这两个分类群之间的关系，本研究进行了相关的系统发育分析、核型分析、微观孢子观察和形态学研究。此外，根据使用三个叶绿体DNA标记atpA、atpB和rbcL构建的系统发育树，利用GTR模型估计了肾叶铁线蕨中华变种和肾叶铁线蕨原变种之间的分化时间。
系统发育结果和分化时间分析——来自4个不同种群（代表所有生物地理分布）的肾叶铁线蕨中华变种的所有个体聚为一个分支，来自7个不同种群（涵盖所有生物地理分布）的肾叶铁线蕨原变种的所有个体聚为另一个分支。肾叶铁线蕨原变种和肾叶铁线蕨中华变种之间的分化时间估计为4.94（2.26 - 8.66）百万年。基于核型分析，推断肾叶铁线蕨原变种为六倍体，2n = 180，X = 30，而肾叶铁线蕨中华变种为四倍体。微观孢子观察表明，肾叶铁线蕨原变种的表面纹饰为光滑型，而肾叶铁线蕨中华变种的为皱波型。肾叶铁线蕨中华变种的叶片为膜质、肾形且有几条明显的同心环，而肾叶铁线蕨原变种的叶片为厚叶、革质且更圆，类似棕榈叶。
肾叶铁线蕨中华变种是一个独立的物种，而非肾叶铁线蕨原变种的变种。因此，我们认可荷叶铁线蕨（Adiantum nelumboides X. C. Zhang, nom. & stat. nov.）作为合法名称，取代之前的肾叶铁线蕨中华变种。根据系统发育分析、分化估计、相关古地理和古气候资料的结果，确定中国是最有可能的进化中心。
