Angiosperms, also known as flowering plants, have about 300,000 species, and are the subphylum of terrestrial plants with the highest degree of diversity, the widest distribution and the strongest adaptability of seed plant phylum. The rise of angiosperms in the Early Cretaceous has reshaped the global landscape of terrestrial vegetation and ecosystems, providing habitats, food and energy sources for the diversification of insects, reptiles, birds and mammals. Since Darwin's theory of evolution was proposed, reconstructing the tree of life of angiosperms has been a hot topic in botany research. In the past 30 years, with the rise of branch systematics and molecular systematics, the study of angiosperm phylogeny has continued to make progress, from the initial dichotomy of dividing the subphylum of the dendritic plant subphylum into monocotyledonous plants and dicotyledonous plants according to morphological and anatomical characteristics to the apg system proposed in 1998 based on the results of molecular systematics research (an order-level system without class or suborder). In recent years, with the great progress made in the study of angiosperm evolution, the apg system has also been updated to the fourth edition (apg iv) and widely adopted. However, the phylogenetic relationships between some of the main branches of angiosperms are not clear, such as the relationship between the eight main branches has not been well analyzed, the relationship between the five branches of the core angiospermae (mesangiospermae) is still unclear, and many phylogenetic relationships at the order and family levels need to be solved urgently.
The research team led by Li Deba, a researcher at the Kunming Institute of Botany, Chinese Academy of Sciences, has been committed to the study of angiosperm phylogeny for many years. Relying on the national major scientific and technological infrastructure "Southwest China Wildlife Germplasm Resource Bank", the team has carried out comprehensive sampling at the family level of angiosperms worldwide through cooperation with the University of Florida, the Texas Institute of Botanic Research, the University of Washington in Seattle, the Royal Botanic Gardens hill garden and the Royal Botanic Gardens of Edinburgh, the University of Johannesburg in South Africa and curtin University in Australia, and has achieved a series of research results through collaborative research. Following the publication of important results (PPA) in the origin and early evolution of angiosperms in Nature Plants in 2019, the phylogenetic genomics of the most complete sampling at the family level of angiosperms was carried out. The study took 162 species of 77 genera in 8 orders, 12 families, and 77 genera of gymnosperms as exoplant groups, selected 416 families of angiosperms recognized by the apg iv system and 17 families accepted by the angiosperm phylogeny website, covering 80 genes of 4792 chloroplast genomes of 4660 species in all 433 families and 2024 genera, and constructed the most complete "tree of life" at the angiosperm level so far.
Based on the phylogenetic tree of angiosperm chloroplasts in 2019, the chloroplast genome data of 73 families was added, and the phylogeny of angiosperms based on chloroplast phylogenetic tree 2.0 (ppa ii) was constructed, and the phylogenetic relationship at the family level of angiosperm was deeply analyzed, of which more than 75% of the relationships between orders and above and 78% of the relationships at the family level and above were supported by 90% or higher. On the basis of the original, the study proposes to adjust all angiosperms from the original 64 orders to 68 orders, that is, the four families of dasypogonaceae, huaceae, oncothecaceae, and sabiaceae are independent of four orders, namely dasypogonales, huales, oncothecales, and sabiales, and recommend that the 20 main branches of the plant be treated as superorders. The eight main branches of angiosperms include the basal order amborellales, nymphaeales, and magnolitans, as well as the five major branches of the core angiosperms, chloranthales, magnoliids, monocots, and monocots. In-depth studies of the relationship between the ceratophyllales and eudicots systems suggest that rapid radiation evolution of core angiosperms may occur early in differentiation. In addition to several orders that have undergone radiation differentiation, such as Apatosaurus, Tiger's Ear, Rhododendron and Labial order, as well as rafflesiaceae, which may have completely lost chloroplast genes, and 4 other heterotrophic plant families apodanthaceae, balanophoraceae, mitrastemonaceae and thismiaceae, Most of the phylogenetic relationships at the order and section levels have been well analyzed, and it is expected to fully update the apg IV system.
On October 29, the results of the study were published online in the international biological journal BMC Biology. The research was supported by the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences, the Open Research Project of major scientific and technological infrastructure of the Chinese Academy of Sciences, the International (Regional) Key Cooperative Research Project of the National Natural Science Foundation of China, the Special Project of The Survey of Basic Resources of Science and Technology, the Open Research Project of the Germplasm Resource Bank, the National Natural Science Foundation of China, the Youth Promotion Association of the Chinese Academy of Sciences and the Yunling High-end Foreign Expert Project, and the preliminary work was initiated through the iflora Research Program of the Kunming Institute of Botany.
Schematic diagram of the angiosperm level tree of life showing the phylogenetic relationships of all 68 orders and 20 superorders (i-xx).
Figure 2: Schematic diagram of the angiosperm level tree of life showing the phylogenetic relationships of all 20 superorders and 433 families, of which 5 dotted families (apodanthaceae, balanophoraceae, mitrastemonaceae, rafflesiaceae and thismiaceae) are set according to the original findings.
Source: Kunming Institute of Botany, Chinese Academy of Sciences