Saxifraga cataphracta, a new species of Saxifragaceae from Southwest China, is described and illustrated. Morphological and molecular evidence (matK, psbA-trnH, psaJ-rpl33) indicate that S. cataphracta belongs to S. sect. Irregulares, and closely related to S. geifolia and S. mengtzeana. The new species can be diagnosed by its leaf blade abaxially with white or virescent interveinal streaks, involucre and bracts conspicuous, capsule beaks winged when mature.

In the Flora of China account (Pan et al. 2001) of Saxifraga mengtzeana Engl. & Irmsch., eight synonyms were attributed to it and one variant, recognised as S. epiphylla Gornall & Ohba, was split from it. This study re-evaluates the taxonomic status of some of the synonyms and of the segregated species in the light of new evidence presented here. Morphological and molecular evidence demonstrate that populations from north-western Yunnan and Sichuan are genetically differentiated from those in south-eastern Yunnan and neighbouring Guangxi. Observations in the field and in cultivation show that the peltate petiole attachment diagnostic of S. mengtzeana var. peltifolia Engl. & Irmsch. is developmentally labile. Similar observations combined with molecular data show that viviparous phenotypes, formerly treated as S. epiphylla, although largely under genetic control, occur sporadically throughout the ranges of both northern and southern taxa. Populations from north-western Yunnan and Sichuan are best recognised as S. geifolia Balf.f., whereas those from south-eastern Yunnan and neighbouring Guangxi are S. mengtzeana. Peltate-leaved variants of the latter are given no status and are relegated to complete synonymy. Viviparous phenotypes of S. mengtzeana are demoted to the rank of forma, as f. epiphylla; analogous phenotypes of S. geifolia are newly described as f. vivipara. Keywords China, Saxifragaceae, Phylogeny, Morphology, Taxonomy