利用整合分类学方法进行蕨类植物复合体的物种划分: 以线裂铁角蕨复合体为例

广泛的杂交和多倍化使得铁角蕨属(Asplenium)下存在着许多分类困难的物种复合体, 针对这些类群进行整合分类学的研究, 有助于我们更加全面和深入地理解物种的界限以及形成机制。线裂铁角蕨复合体(Asplenium coenobiale complex)是铁角蕨属下一个形态多样性较高的类群, 由于缺乏全面取样和系统研究, 该复合体的物种划分长期存在争议。本研究选取线裂铁角蕨复合体中形态变异和地理分布具有代表性的个体, 通过孢粉学研究确定该类群的生殖特性, 运用流式细胞分析获取倍性信息, 同时结合叶绿体和核基因组片段系统发生分析的证据, 对该类群的系统演化关系和起源方式进行了探讨。结果表明: (1)虽然部分孢子囊败育的情况在线裂铁角蕨复合体中十分普遍, 但正常孢子囊内形成的64个孢子说明该类群植物仍能进行正常的有性生殖; (2)该复合体中存在着倍性变异, 其中多角铁角蕨(A. cornutissimum)是二倍体, 而其他成员均为四倍体; (3)依据母系遗传的叶绿体序列所构建的系统发生关系将该类群划为4个分支, 与基于核基因序列构建的系统树存在冲突, 这暗示杂交可能在该复合体的形成过程中起到了重要的推动作用。综上所述, 我们建议将线裂铁角蕨复合体划分为4个物种, 即同源四倍体新种马关铁角蕨(A. maguanense sp. nov.), 二倍体多角铁角蕨, 以及两个由同一对亲本正反交产生的异源四倍体线裂铁角蕨(A. coenobiale)和叶基宽铁角蕨(A. pulcherrimum)。

Integrative taxonomy resolved species delimitation in a fern complex: A case study of the Asplenium coenobiale complex

Due to wide hybridization and polyploidization, there are numerous species complexes with taxonomic challenges in the fern genus Asplenium. Integrative taxonomy using evidence of morphology, cytology and molecular phylogeny provides one of the best ways for the discovery and delimitation of species. The Asplenium coenobiale complex represents one of the spleenwort complexes, which are morphologically variable and difficult in species delimitation. Owing to the lack of comprehensive sampling and systematic study, the taxonomy of this complex remains unresolved. In this study, we selected representative individuals of this complex covering differences in morphology and geography. We conducted a palynological study to explore reproductive characteristics, and inferred the ploidy level through flow cytometry. Furthermore, based on the phylogenetic evidence from chloroplast and nuclear genomes, we discussed the evolutionary relationship and origin of this complex. Our results showed that: (1) The development of 64 spores within a single normal sporangium is indicative of the ability of sexual reproduction, although abortive sporangia are common in the Asplenium coenobiale complex. (2) Ploidy variation is found in this complex, i.e. A. cornutissimum is diploid, whereas other members are all tetraploid. (3) The maternally inherited chloroplast phylogeny supported four clades within this complex, and this was incongruent with the nuclear phylogeny; therefore, it was inferred that hybridization could be an important driving force during the formation of the complex. Based on our analyses, we conduct a revision to the A. coenobiale complex, i.e. one newly discovered autotetraploid species (A. maguanense sp. nov.), one diploid species (A. cornutissimum), and two allotetraploids with reciprocal origins (A. coenobiale and A. pulcherrimum).