Molecular phylogenetics, morphology and a revised classification of the complex genus Saxifraga (Saxifragaceae)

Abstract

Saxifraga, the most species‐rich and taxonomically complex genus of Saxifragaceae, is a characteristic component of temperate to polar climatic zones and of montane to alpine vegetation belts in mountain ranges of the Northern Hemisphere. The genus encompasses more than 440 species, which display notable diversity in growth form, vegetative and reproductive characters, as well as in micromorphology of pollen grains and seeds. Using a large taxon set including representatives attributed to nearly all recognised subgenera, sections and subsections of Saxifraga (altogether 254 species), as well as a broad coverage of outgroup taxa, we inferred evolutionary relationships within Saxifraga, explored the reasons of the striking inconsistencies between previous taxonomic treatments of Saxifraga, estimated the degree of homoplasy in characters frequently employed for classification, assessed the role of hybridisation in the evolution of the genus and, finally, provided a phylogeny‐based framework upon which to revise its taxonomy. The phylogenetic trees based on nuclear ribosomal internal transcribed spacer (ITS) and plastid trnL‐trnF DNA markers, including more than 460 newly generated sequences, were generally highly congruent, except within a single clade (sect. Saxifraga), in which incomplete lineage sorting and presumably allopolyploid speciation plays an important evolutionary role. Major lineages of Saxifraga are concordantly resolved by the DNA markers from both organelles with mostly strong node support. Our molecular phylogenetic results support the recognition of at least 13 sections and 9 subsections within Saxifraga. A part of these lineages agrees well with previously recognised infrageneric groupings, whereas others are differently delineated. Some of the groups identified by molecular phylogenetics are characterised only by the combination of different morphological characters. Frequently, micromorphological characters support the clades in the phylogenetic tree comparatively well. We here provide new ranks for three infrageneric epithets, namely for sect. Saxifragasubsect. Androsaceae and subsect. Arachnoideae and sect. Porphyrion subsect. Squarrosae. Finally, our study identifies remaining taxonomic uncertainties within Saxifraga.

Ecological niche differences between two polyploid cytotypes ofSaxifraga rosacea

“…More recently, Tkach et al. () found S. terektensis , S. cespitosa ssp. monticola and S. hypnoides to be closely related to S. rosacea .…”

“…Saxifraga, Vargas (2000) identified a polytomic subclade consisting of S. rosacea, S. hartii, S. graeca, S. granulata and S. cespitosa. More recently, Tkach et al (2015) found S. terektensis, S. cespitosa ssp. monticola and S. hypnoides to be closely related to S. rosacea.…”

Development of EST‐SSR markers in Saxifraga sinomontana (Saxifragaceae) and cross‐amplification in three related species

“…The genus Saxifraga L. (Saxifragaceae) consists of approximately 500 species that are mainly distributed in the mountainous regions of Europe and Asia (Pan et al., ; Gao et al., ; Tkach et al., ), including the Qinghai–Tibetan Plateau (QTP) and Hengduan Mountains region (HDM), which is a biodiversity hotspot of Saxifraga (Pan et al., ). Saxifraga sinomontana J. T. Pan & Gornall is a widespread perennial herb in the QTP and its peripheral regions.…”

“…However, S. sinomontana is an extraordinarily variable species in morphology, as described in the Flora of China (Pan et al., ), as well as according to our long‐term field surveys, which have demonstrated that gradations in traits are common in the species (e.g., plant height, number of flowers). Saxifraga sinomontana has been the focus of recent systematics research (Gao et al., ; Tkach et al., ), and Li et al. () revealed that this species possesses a high level of genetic diversity, which may be the result of Quaternary climatic oscillations.…”

Development and characterization of EST‐SSR markers for Saxifraga fortunei var. incisolobata (Saxifragaceae)

“…Saxifraga L. is the largest genus in the Saxifragaceae family, with more than 440 species widely distributed throughout the Northern Hemisphere (Tkach et al., ). A recent phylogenetic study divided this genus into 13 sections and nine subsections, with section Irregulares Haw., a well characterized group with zygomorphic flowers, as the earliest diverged lineage (Tkach et al., ). This section comprises 15–20 species growing in moist temperate areas of East Asia, whereas most other sections of Saxifraga are widely distributed in boreal and/or alpine areas (Pan, ).…”