Saxifragaviridiflora (Saxifragaceae), an unusual new species from Guangxi, China

Abstract Saxifragaviridiflora, a remarkable new species of the genus Saxifragasect.Irregulares (Saxifragaceae) from Guangxi, is described and illustrated herein. This new species morphologically differs from all known S.sect.Irregulares taxa by its greenish petals, verruculose sepals, and thick leathery leaf blade abaxially scarlet with white spots.

China has a vast territory with a wide range of complex and diverse topographies and soils and covering several climate types, which contribute to the wealth of Chinese botanical diversity (Sun et al. 2017;Chen et al. 2018 (Zhao et al. 2019).

Saxifraga viridiflora
Etymology. The specific epithet refers to the flowers of this new species that are green throughout the flowering period, differing from those of all other known Saxifraga sect. Irregulares species. The Chinese name is given as "绿花虎耳草" (lǜ huā hǔ ěr cǎo), referring to the greenish petals of the new species.
Phenology. In a two year personal observation of this new species in its native range, Guangxi. Guilin City (Luo Dexuan, pers. comm.), S. viridiflora was flowering from April to July and fruiting from June to August.
Distribution and ecology. The new species, Saxifraga viridiflora, is currently known only from Yongfu County, Guangxi Province, China. It was observed to grow on dry limestone under dense jungles at altitudes between 500 and 600 m. Paratypes

Discussion
The new species Saxifraga viridiflora has zygomorphic flowers and stolons absent, which indicate a position in S. sect. Irregulares ser. Rufescentes. Saxifraga viridiflora is distinct from all known sect. Irregulares taxa by its greenish petals, verruculose sepals, and thick leathery leaf blade abaxially scarlet with white spots.
Geographically, Saxifraga viridiflora was only found in Yongfu County of Guangxi Province, China. It grows only on dry rocks under dense jungles in limestone area, whereas other related species of sect. Irregulares usually grow on damp cliffs and rocks nearby valleys. Here we argue that the environmental heterogeneity plays an important role in the differentiation of the species in sect. Irregulares, given the leaf blade of Saxifraga viridiflora is thick leathery or fleshy (grow on dry rocks), while the leaf blade of other related species of sect. Irregulares are mainly papery or leathery (grow on damp rocks).
Notably, only seven species of Saxifraga sect. Irregulares were recorded in "Flora of China" (Pan et al. 2001). However, six new species of S. sect. Irregulares were discovered in China in recent years, provided that Saxifraga viridiflora is counted. Furthermore, most of these new species were confined to a narrow geographical range. Species richness of S. sect. Irregulares has been quite underrated, and more field investigations and phylogenetic analyses are needed to infer its biodiversity and speciation history.
Since several new species of S. sect. Irregulares have been published in recent years, we include here an identification key to include all species known so far for this section.
Identification key to Saxifraga sect. Irregulares