The Circaeasteraceae (Ranunculales) contains only two species, Circaeaster agrestis and Kingdonia uniflora, both of which are national key protected wild plants in China. These two species possess the same distinctive dichotomous venation, which is very rare among angiosperms. 

In order to better understand the plastome evolution in early-diverging angiosperms, Dr. SUN Yanxia under the supervision of Prof. LI Jianqiang and Prof. WANG Hengchang from Wuhan Botanical Garden determined the whole plastome sequences of Circaeaster agrestis and Kingdonia uniflora, and conducted the phylogenomic analyses among seven Ranunculales families.  

A large ~49 kb inversion and a small ~3.5 kb inversion were found in both plastomes; one rare rearrangement was detected in the Inverted Repeat region of Circaeaster agrestis plastome; all ndh genes, except for ndhE and ndhJ, were found to be either pseudogenized or absent in the Kingdonia uniflora plastome. All the characters described above are Circaeasteraceae plastome specific. Circaeasteraceae was strongly supported as sister to Lardizabalaceae in the phylogenomic analyses. 

The plastomes of these two species provide the first reference genome sequences for Circaeasteraceae, which will enrich the sequence resources of plastomes in early-diverging eudicots. The unusual rearrangements detected in Circaeasteraceae plastomes help to better characterize plastome structural evolution in early-diverging eudicots. 

This work was supported by the National Natural Science Foundation of China, NSTIPC  and SPRPCAS. Results have been published in BMC Genomics entitled “Complete plastome sequencing of both living species of Circaeasteraceae (Ranunculales) reveals unusual rearrangements and the loss of the ndh gene family”.  

Plastome maps of Circaeaster agrestis and Kingdonia uniflora (top left corner); and phylogenetic relationships within Ranunculales (Image by SUN Yanxia)