Floral Organogenesis In Berberidoideae And Nandinoideae(Berberidaceae) And Species Delimitation Of Mahonia

The family of Berberidaceae(Ranunculales)belongs to the basal eudicots,which is the important medicinal resources and has wide range of ornamental value.The inflorescences and floral organs of Berberidaceae exhibit high diversity,serving as an important window for understanding the evolutionary patterns of inflorescences and floral organs in Ranunculales.However,previous studies on the floral organogenesis in different taxa within Berberidaceae are limited to some sporadic reports.The processes of the formation and evolution of flowers remain unclear.The accurate identification of medicinal taxa faces significant challenges.In the era of molecular biology,morphological data are still beneficial to improve the efficiency of species identification.We respectively selected one representative species from Berberis and Mahonia(Berberidoideae);Nandina and Caulophyllum(Nandinoideae).Scanning electron microscopy(SEM)was employed to observe the developmental stages of inflorescences and flower.Thirty Chloroplast genomes from 19 Mahonia species and 10 outgroup species were used to develop an integrated "molecular + micromorphological" method for species identification.The results indicate that:The inflorescence of Nandina is not a typical panicle because the terminal flower on the raceme branch opens first.The inflorescence of Caulophyllum is a thyrse rather than the previously described panicle or cyme.The inflorescences of Berberis thunbergii var.atropurpurea and Mahonia fortunei are fasciated umbel and raceme,respectively.Floral organs of the four genera are centripetally initiated and mostly are arranged in trimerous whorls.However,in Berberis thunbergii var.atropurpurea,the terminal flower exhibits pentamerous and 2/5 spiral arrangement,that the petals are inserted opposite to the stamens.The occurrence of petal-stamen common primordia has not been observed during the development of the four genera.The presence of petal-stamen common primordia may be resulted from the incomplete developmental stages.The petal of Nandina are not nectariferous.The nectary tissue of Caulophyllum is distributed at the top of petals.In Berberis and Mahonia,two saccular protuberances at the basal part of petal are nectary.Anthers are longitudinal dehiscent in Nandina or valvate in other three genera.Except for typical tricolporate pollen,the genera Berberis and Mahonia exhibit multicolporate pollen.The placenta is marginal in Nandina,and is basal in other three genera.Mature ovules are anatropous and bitegmic and possess pock-like outer integument.The genera of Berberis and Mahonia possess short and swollen funicles with distinct funicular appendages.The funicles in Nandina is short,but in Caulophyllum is long.Based on the evidence of floral morphogenesis,it supports the view from molecular data that Nandina is a member of Berberidaceae but with some specific characters,and Mahonia is a different genus from Berberis,should be separated from Berberis.The chloroplast genomes of the Mahonia and Berberis comprise ca.10 kb expansion of the inverted repeat(IR)region,representing a typical feature of the chloroplast genomes of Berberideae.The results support that Mahonia and Berberis have a closer relationship than other genera in Berberidaceae.There are abundant SSRs and dispersed repeated sequences in the plastomes of Mahonia,which may provide genetic resources to develop molecular marker of Mahonia.Topological incongruence between the chloroplast and nuclear phylogenetic tree of the genus Mahonia indicates ancestral hybridization events and/or incomplete lineage sorting possibly.The phylogenetic tree based on eight hypervariable sequences have similar topological structure with the tree based on plastomes,which can be a substitution to resolve phylogenetic relationships within Mahonia.The combination of special barcoding and leaf epidermal micro-morphological data significantly improves the success rate of species identification in the genus Mahonia,providing a valuable template for species delimitation in other complex groups.This study provides detailed observations on the development of inflorescences and floral organogenesis in Berberidoideae and Nandinoideae,contributing to a deeper understanding of the evolutionary patterns of floral characters in angiosperms.We also achieved scientific species delimitation using a combined molecular and micromorphological approach,and provided new insights for comprehensive delimitation in other taxonomic groups.