Discussion
Comparative genomics of Saxifragales
Although seven species from four families of Saxifragales have published whole-genome sequence assemblies (Fu et al., 2017; Yang et al., 2017 ; Wai et al., 2019 ; Lv et al., 2020; Zhu et al., 2020; Korgaonkar et al., 2021 ), only those of Paeonia ostii and Cercidiphyllum japonicum were assembled at the chromosomal level. Here, we successfully assembled the genome ofTiarella polyphylla , which is the first chromosome-level sequencing, assembly, and annotation of the genome of Saxifragaceae. The final size is 412.2 Mb, similar to the estimated genome size (393.29 Mb) based on k-mer analysis. It is much smaller than estimates reported in other genera of Saxifragaceae tribe Heuchereae (e.g., Mitella diphylla , 1C = 0.57 pg; Bai et al., 2012 ; Heuchera cylindrica, 1C = 0.48–0.52 pg; Godsoe et al., 2013 ). Our results demonstrated that T. polyphylla , C. japonicum andHamamelis virginiana had no additional genome duplication after the ancestral gamma hexaploidization event shared with all core eudicots. These three genera span Saxifragales, demonstrating that there is no ancestral genome-wide duplication characteristic of the entire order. More details on comparative genomics and whole-genome duplication are available in Discussion S1.