Discussion
The new species Saxifraga cataphracta has asymmetric flowers with two elongated petals and stolons absent, which indicate a position in S. sect.Irregulares ser. Rufescentes J.T.Pan. Previously phylogenetic analyses reveal that spots on abaxial leaf surface are phylogenetically informative within S. sect. Irregulares ser. Rufescentes , that is, the ser. Rufescentes can be divided into two subclades according to spots on leaves (abaxially spotted vs. abaxially unspotted) (Zhang et al. 2020). The new species S. cataphracta was nested in the spotted subclade (contained S. geifolia , S. mengtzeana , S. viridiflora X.J.Zhang, T.Deng, J.T.Chen & H.Sun,S. daqiaoensis F.G.Wang & F.W.Xing, S. luoxiaoensis W.B.Liao, L.Wang & X.J.Zhang, S. kwangsiensis Chun & F.C.How ex C.Z.Gao & G.Z.Li, S. damingshanensis W.B.Liao, W.Y.Zhao & J.H.Jin, and S. kegangii D.G.Zhang, Ying Meng & M.H.Zhang). However, S. cataphracta is distinct from all other spotted species by its abaxial leaf surface covered white or virescent streaks rather than spots (Figs 1&2). Additionally, foliar embryos were found in S. cataphracta . There are only two species with foliar embryos in known species ofS. sect. Irregulares —S. geifolia and S. mengtzeana . It is worth noting that S. geifolia was restored, and S. epiphylla (with foliar embryos) was synonymized underS. mengtzeana recently (Zhang et al. 2022a). Of these three species with foliar embryos, S. cataphracta is morphologically similar to S. geifolia , as the leaf blade of these two species is rotund to reniform, more or less isodiametric, while the leaf blade ofS. mengtzeana is triangular-ovate leaves, longer than wide (Fig. 2). Molecular phylogenetic analyses also reveal a close relationship between S. cataphracta and S. geifolia (Fig. 3). However,S.cataphractacan easily be distinguished from S. geifolia by its unusual streaks in the abaxial leaf surface and other morphological features as discussed above (see Results).
Geographically, Saxifraga cataphracta was distributed in northeastern Yunnan, Chongqing and southern Sichuan, which is on the east of the distribution area of S . geifolia (Fig. 4). Here we argue that the environmental heterogeneity plays an important role in the differentiation of these species. More investigations and phylogenetic analyses are needed to infer the speciation, trait evolution and biogeographic history of S. sect. Irregulares .