Abstract
The woody Sonchus alliance consists primarily of woody species of the genus Sonchus (subgenus Dendrosonchus; family Asteraceae). Most members of the alliance are endemic to the oceanic archipelagos in the phytogeographic region of Macaronesia. They display extensive morphological, ecological, and anatomical diversity, likely caused by the diverse habitats on islands and rapid adaptive radiation. As a premier example of adaptive radiation and insular woodiness of species endemic to oceanic islands, the alliance has been the subject of intensive evolutionary studies. While phylogenetic studies suggested that it is monophyletic and its major lineages radiated rapidly early in the evolutionary history of this group, genetic mechanisms of speciation and genomic evolution within the alliance remain to be investigated. We first attempted to address chloroplast (cp) genome evolution by conducting comparative genomic analysis of three representative endemic species (Sonchus acaulis, Sonchus canariensis, and Sonchus webbii) from the Canary Islands. Despite extensive morphological, anatomical, and ecological differences among them, their cp genomes were highly conserved in gene order and content, ranging from 152,071 to 152,194 bp in total length. The number of repeat variations and six highly variable regions were identified as valuable molecular markers. Phylogenetic analysis of 32 species in the family Asteraceae revealed the phylogenetic position of the woody Sonchus alliance within the tribe Cichorieae and the sister relationship between the weedy Sonchus oleraceus and the alliance.
Highlights
The current, redefined genus Sonchus (Asteraceae) in its wider circumscription is comprised of ca. 95 species, consisting of the subgenera Dendroseris, Dendrosonchus, and Origosonchus and other widely distributed weedy species that are tentatively classified under the subgenus Sonchus [1,2].Sonchus is widely distributed, extending from the Mediterranean region to the mid-Atlantic islands, temperate Eurasia, tropical Africa, Australia/New Zealand, North America, and the South PacificJuan Fernández and Desventuradas Islands [1]
Anatomical, and ecological differences among three Sonchus species (i.e., S. canariensis, S. webbii, and S. acaulis), pairwise identity among their complete chloroplast genomes was strikingly high in sequence (99.6%), gene content, and organization
These two chloroplast DNA (cpDNA) inversions unique in Asteraceae are shared by all major clades of Asteraceae except members of subfamily Barnadesioideae distributed in Andes, South America, as reported in comparison with other outgroup species in Campanulaceae, Goodeniaceae, Ericaceae, Pittosporaceae and Nicotiana tabacum (Solanaceae), which do not have them [28,29]
Summary
The current, redefined genus Sonchus (Asteraceae) in its wider circumscription is comprised of ca. 95 species, consisting of the subgenera Dendroseris, Dendrosonchus, and Origosonchus and other widely distributed weedy species that are tentatively classified under the subgenus Sonchus [1,2].Sonchus is widely distributed, extending from the Mediterranean region to the mid-Atlantic islands, temperate Eurasia, tropical Africa, Australia/New Zealand, North America, and the South PacificJuan Fernández and Desventuradas Islands [1]. 95 species, consisting of the subgenera Dendroseris, Dendrosonchus, and Origosonchus and other widely distributed weedy species that are tentatively classified under the subgenus Sonchus [1,2]. While the subgenus Dendroseris includes the endemic species of the Pacific islands distributed in the archipelagos of Juan Fernández and Desventuradas, the subgenus Origosonchus is mainly distributed in Africa, with some species occurring in Asia (Saudi Arabia and Yemen). The subgenus Dendrosonchus consists of approximately 35 woody species, known as the woody Sonchus alliance, distributed in the Macaronesian Islands of the Atlantic Ocean, Genes 2019, 10, 217; doi:10.3390/genes10030217 www.mdpi.com/journal/genes. The entire alliance is endemic to the Macaronesian Islands, with the exception of one species, Sonchus pinnatifidus, occurring in both the Canaries and western
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