Pollen Morphology and Plastome Phylogeny of Genus Ligusticopsis and Related Species in China
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    Abstract:

    The pollen morphology of eight species from Ligusticopsis and two species from its relatives (ten species in total) from Apiaceae subfamily Apioideae was observed and studied by scanning electron microscopy and light microscopy, combining with plastome phylogenetic tree to explore the phylogenetic status of Ligusticopsis and to propose advice on taxonomic treatment, aim to provide pollen morphological evidence for the systematic classification of Ligusticopsis. The results indicated that: (1) the pollen of ten species from Ligusticopsis and its relatives from subfamily Apioideae had a ratio of polar axis length to equatorial axis length (P/E) was 1.89-2.31, pollen size varied from 25.45-41.70 × 11.29-20.52 μm, there are four types of pollen morphology: subrectangular, subrectangularequatorially contracted, long subelliptical, and subrhombic, the apertures are all pleurotremes. (2) Scanning electron microscopy revealed that there are six types of polar sculptures: striate reticulate, thin perforated reticulate, perforatedstriate reticulate, smooth pitted reticulate, smooth perforated reticulate, and striate; there are two types of pollen in polar view: trilobatecircular and intersemilobate, which are the more primitive to the more evolved pollen types of the Apiaceae. (3) Pollen morphology shows that the pollen of Ligusticopsis are all subrectangular, with striate reticulate and perforated reticulate sculptures under SEM, making it a relatively natural taxon, which supported that Ligusticopsis should be an independent genus from “Ligusticum sensu lato”, but the pollen of L. pteridophylla is subrhombic, a relatively primitive pollen type in Apioideae. (4) Molecular phylogenetic studies show that nine species form a separate monophyletic branch (Subclade A) within Selineae containing the type species of Ligusticopsis (L. rechingerana), and seven species of ten species from Ligusticopsis and its relatives all located within Subclade A, which forms a monophyletic branch of the genus Ligusticopsis in the phylogenetic tree based on plastome, i.e., molecular evidence for the phylogenetic independence of Ligusticopsis and its position is under Selineae, but L. pteridophylla forms a separate basal outgrowth branch in Hymenidium Clade, indicating that L. pteridophylla has a unique phylogenetic position and does not belong to either Ligusticopsis or Ligusticum. The results suggest that Ligusticopsis is a young genus that diverged from the same ancestor, possibly as a result of the formation of an ancestral species that originated in PanEast Asia and spread westwards and across the QinghaiTibet Plateau, with rapid adaptive radiation in East Asia to the ChinaHimalaya region. In this study, it is suggested that Ligusticopsis angelicifolia should be placed into Angelica, Selinum wallichianum and Ligusticum hispidum should be transferred into Ligusticopsis, Ligusticopsis acuminata should be included in Ligusticum; further study is requested for the phylogenetic status of L. pteridophylla.

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LI Zixuan, ZHOU Songdong, HE Xingjin. Pollen Morphology and Plastome Phylogeny of Genus Ligusticopsis and Related Species in China[J]. Acta Botanica Boreali-Occidentalia Sinica,2022,42(12):2030-2041

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  • Online: January 15,2023
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