Abstract
Buddleja colvilei Hook.f. & Thomson (Scrophulariaceae) is a threatened alpine plant with a distribution throughout the Himalayas, also used as an ornamental plant. The name Buddleja sessilifolia B.S. Sun ex S.Y. Pao was assigned in 1983 to a plant distributed throughout the Gaoligong Mountains, but the name was later placed in synonymy with B. colvilei in the Flora of China. In this study we sequenced the complete chloroplast (cp) genomes of two individuals of B. colvilei and three individuals of B. sessilifolia from across the range. Both molecular and morphological analysis support the revision of B. sessilifolia. The phylogenetic analysis constructed with the whole cp genomes, the large single-copy regions (LSC), small single-copy regions (SSC), inverted repeat (IR) and the nuclear genes 18S/ITS1/5.8S/ITS2/28S all supported B. sessilifolia as a distinct species. Additionally, coalescence-based species delimitation methods (bGMYC, bPTP) using the whole chloroplast datasets also supported B. sessilifolia as a distinct species. The results suggest that the B. sessilifolia lineage was early diverging among the Asian Buddleja species. Overall gene contents were similar and gene arrangements were found to be highly conserved in the two species, however, fixed differences were found between the two species. A total of 474 single nucleotide polymorphisms (SNPs) were identified between the two species. The Principal Coordinate Analysis of the morphological characters resolved two groups and supported B. sessilifolia as a distinct species. Discrimination of B. colvilei and B. sessilifolia using morphological characters and the redescription of B. sessilifolia are detailed here.
Highlights
The Himalayan region is a center of diversity for the genus Buddleja L. (Scrophulariaceae) [1], harboring 75% of the Asian Buddleja species (18 of 24 species)
The cp genomes from two B. colvilei individuals and three B. sessilifolia individuals were sequenced, analyzed, and compared
The phylogenetic analyses constructed with the whole cp genomes, the large single-copy regions (LSC), small single-copy regions (SSC), inverted repeat (IR) and the nuclear genes
Summary
The Himalayan region is a center of diversity for the genus Buddleja L. (Scrophulariaceae) [1], harboring 75% of the Asian Buddleja species (18 of 24 species). Many species in the genus Buddleja are famous as ornamentals [2,3]. Buddleja colvilei is a shrub or small tree [6,7], and as an ornamental plant, it was awarded the Royal Horticultural Society (RHS) First Class Certificate and the outstanding excellence for exhibition for the high ornamental. 2 offor (RHS) First Class Certificate and the outstanding excellence for exhibition the high ornamental value [4]. It is endemic to the eastern Himalayas, and has a distribution across altitudes of 1600–4200 m, in Nepal, India (Sikkim), Bhutan, and China (Tibet, Yunnan) [6]. It is endemic to the eastern Himalayas, and has a distribution across altitudes of 1600–4200 m, it is only found in Yadong, Tibet and the Gaoligong Mountains in Yunnan. In China, it is only found in Yadong, Red List has evaluated B. colvilei as Vulnerable (VU) [8], the species has not yet been
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