Plastomes Provide Insights into Differences between Morphology and Molecular Phylogeny: Ostericum and Angelica (Apiaceae) as an Example

Traditional classification based on morphological characters suggests that the genus Ostericum is closely related to Angelica, but molecular phylogenetic studies suggest that the genus Ostericum is related to Pternopetalum rather than Angelica. In this study, the plastomes of nine Ostericum species and five Angelica species were used to conduct bioinformatic and comparative analyses. The plastomes of Ostericum and Angelica exhibited significant differences in genome size, gene numbers, IR junctions, nucleotide diversity, divergent regions, and the repeat units of SSR types. In contrast, Ostericum is more similar to Pternopetalum rather than Angelica in comparative genomics analyses. In total, 80 protein-coding genes from 97 complete plastomes and 112 ITS sequences were used to reconstruct phylogenetic trees. Phylogenies showed that Angelica was mainly located in Selineae tribe while Ostericum was a sister to Pternopetalum and occurred in the Acronema clade. However, morphological analysis was inconsistent with molecular phylogenetic analysis: Angelica and Ostericum have similar fruit morphological characteristics while the fruits of Ostericum are quite different from the genus Pternopetalum. The phylogenetic relationship between Angelica and Ostericum is consistent with the results of plastome comparisons but discordant with morphological characters. The cause of this phenomenon may be convergent morphology and incomplete lineage sorting (ILS).