Abstract
The Arcto-Tertiary relict genera, Camptotheca, Davidia, and Nyssa represent deep lineages in the asterid order Cornales. Recent phylogenetic studies suggested that these genera should be placed in a newly circumscribed family, Nyssaceae. However, because these analyses were based upon a few genes, it is prudent and necessary to examine further evidence before adopting this taxonomic treatment. In this study, we determined the complete chloroplast (cp) genomes of Camptotheca acuminata, Davidia involucrata, and Nyssa sinensis. Their cp genomes ranged from 156,672 to 158,409 bp, which included 115 genes, and their genome features were highly similar to those of other species within the order Cornales. The phylogenetic relationships among the genera Camptotheca, Davidia, Nyssa, and 23 related taxa in the asterids were analyzed based on 73 protein-coding genes from the cp genomes. All of the previously recognized major clades (namely Cornales, Ericales, Campanulids, and Lamiids) in the asterids, as well as their relationships, were recovered with robust support. A clade including the genera Davidia, Nyssa, Camptotheca, and Diplopanax, was resolved as a well-supported monophyletic group, which was fully separated from the family Cornaceae by the family Hydrangeaceae. Our results provide novel evidence to support the acceptance of the family Nyssaceae outlined by the updated Angiosperm Phylogeny Group.
Highlights
The woody dioecious genera, Camptotheca, Davidia, and Nyssa are very likely to be deep branches within the asterid order Cornales (Xiang et al, 2011)
Fresh leaves of Davidia involucrata, N. sinensis, and C. acuminata were collected from the Botanical Garden of Kunming Institute of Botany, Chinese Academy of Sciences; voucher information is presented in Supplementary Table S1
All three genomes, consisting of a pair of inverted repeated (IR) (25,971–25,878 bp) separated by the large single-copy (LSC) (86,184–87,611 bp) and small single-copy (SSC) (18,260–18,856 bp) regions, showed a typical quadripartite structure that is similar to the majority of land plant cp genomes (Figure 1 and Table 1)
Summary
The woody dioecious genera, Camptotheca, Davidia, and Nyssa are very likely to be deep branches within the asterid order Cornales (Xiang et al, 2011). Davidia and Camptotheca have, respectively, only one and two extant species native to subtropical China (Qin and Chamlong, 2007), whereas Nyssa (approximately eight species) has a disjunct distribution in the middle latitudes of East Asia and North America (Wen and Stuessy, 1993). All three genera have extensive fossil records throughout the northern hemisphere during the Paleocene and Neogene The extant species of Camptotheca, Davidia, and Nyssa are excellent examples of ArctoTertiary relicts. Their phylogenetic profiles would deepen our understanding of the evolution of the Arcto-Tertiary flora in the northern hemisphere
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