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 .