Phylogeny, genetics and ecological adaptation of the <i>Chrysanthemum indicum</i> complex

Chrysanthemum indicum L. is a member of the Asteraceae family and its dried capitulum has been utilized for thousands of years in traditional Chinese medicine. The C. indicum complex contains both diploid and polyploid (mainly tetraploid) cytotypes and also has a variety of C. indicum var. aromaticum Q.H.Liu et S.F.Zhang which is endemic to the Shennongjia Forest region. Additionally, two species of C. nankingense (Hand.-Mazz.) X.D.Cui and C. lavandulifolium (Fisch. ex Trautv.) Makino exhibit the strongest evolutionary connections to C. indicum, and natural hybridization between them is common. Due to the extensive natural range of the C. indicum complex in China including many eco-geographic populations, there is a significant amount of variation in its morphology and metabolic makeup. Here, we reviewed the advances in phylogeny, population genetics, and ecological adaptation of the C. indicum complex, as well as those studies involving genomes and functional genes that may help us better understand the molecular mechanisms underlying the complex's phenotypic variation and biogeographic distribution. To enhance the medicinal applications of the C. indicum complex resource, future study should place a greater emphasis on resolving the complicated species relationship, dissecting the transcriptional regulatory network of active components, and enhancing omics data-assisted breeding.