Integrated taxonomy of the Asplenium normale complex (Aspleniaceae) in China and adjacent areas

Abstract

The Asplenium normale D. Don complex comprises several taxa that are either diploid or tetraploid. The tetraploids are assumed to have originated from diploid ancestors by relatively recent autopolyploidization or allopolyploidization. Some of the diploids are readily recognized morphologically but most of the taxa have until now been placed into a single species. However, phylogenetic studies have challenged this treatment and emphasized the notion that the taxonomic treatment of this complex needs to be revised. An integrative taxonomic approach was employed to delimit species in the complex using cytological, morphological, and DNA sequence data. Initially, we employed a diploid first approach to establish a robust taxonomic framework. Special efforts were made to collect and identify the diploid progenitors of each polyploid lineage identified in the plastid DNA based phylogenetic hypothesis. A total of six distinct diploid species were identified. The distinctive nature of the six diploids is strongly supported by sequence differences in plastid DNA and nuclear loci, as well as by the results of morphometric analysis. Diagnostic morphological characters were identified to distinguish the six diploid species, resulting in their revised taxonomy, which includes two novel species, namely, Asplenium normaloides and A. guangdongense. Further studies to strengthen the taxonomic classification of all of the tetraploid taxa are warranted.

A global plastid phylogeny of the fern genus Asplenium (Aspleniaceae)

“…Within the A. trichomanes clade, the 141 accessions representing c . 50 species in our sampling are resolved into five well‐supported subclades: the A. diellia subclade, A. monanthes subclade, A. normale subclade, A. trichomanes subclade and the A. viride subclade, and each of the subclades corresponds to a species complex (Wagner, ; Chang et al., ). The relationships among these subclades are not well‐resolved (Fig.…”

“…It comprises members of the A. normale complex and one species, A. speluncae Christ, with simple laminae, and contains ≥14 species. The distribution of the A. normale subclade ranges from East Africa, Madagascar and throughout the Indian Ocean, Southeast Asia, northern Australia, Pacific islands to Hawaii, South and Central China, and Japan (Chang et al., , ).…”

“…). Molecular studies have focused on delimiting species or reticulate evolution in species complexes involving a few or dozens of species, such as the Appalachian Asplenium complex (Werth et al., ), the New Zealand Asplenium complex (Shepherd et al., ), the A. monanthes complex (Dyer et al., , ), the A. normale complex (Chang et al., , ), and the A. obovatum and A. adiantum‐nigrum complexes (Sessa et al., ). There have been only a few global molecular phylogenies of Asplenium using plastid markers to identify major clades in the genus.…”

Exploring the reticulate evolution in the Asplenium pekinense complex and the A. varians complex (Aspleniaceae)

“…Therefore, frequent diplospory (meiosis aborted at metaphase in diploid spore mother cells with the consequent formation of unreduced spores) in normal diploid progenitor or sterile interspecific hybrid is the ready inception of a new fertile auto‐ or allotetraploid (Lovis, 1977). Reticulate relationships of the A. normale complex (Chang et al, 2013, 2014, 2018), the A. paleaceum complex (Ohlsen et al, 2015), and the A. monanthes complex (Dyer et al, 2012) have been well investigated using evidence from nuclear and plastome genomes. However, our present knowledge about the evolutionary history (summarized in Fig.…”

Virtual issue: Ecology and evolution of pteridophytes in the era of molecular genetics

“…Recent studies have combined plastid and nuclear genes, often in combination with observations of spore size and morphology, to trace hybrid origins and revise taxonomy. Chang et al (2018) utilized a "diploids-first" approach (Beck et al 2010) within an integrative framework including morphology and plastid and nuclear DNA to clarify the taxonomy of the widespread Asplenium normale species complex. Fujiwara et al (2018) incorporated cytology and plastid and nuclear DNA to infer the evolution of Lepisorus in Japan.…”