Begonia pseudoedulis, a new species in Begonia sect. Platycentrum (Klotzsch) A.DC. (Begoniaceae) from southern Guangxi of China, is here described and illustrated. It morphologically resembles B. edulis H.Lév. and B. dielsiana E.Pritz. ex Diels but differs easily by its hairy petioles and inflorescences, and red hispidulous flower tepals, ovary and capsules. The molecular phylogenetic analysis based on ITS supported that the new species was a monophyletic lineage, separating from both B. dielsiana and B. edulis. Due to its isolated distribution with several small populations, which are possibly disturbed by human activities, the species is considered as “Near Threatened” (NT) according to the IUCN Red List Categories and Criteria.

Molecular evidence, morphology, new taxon, southern China, taxonomy

As a pan-tropically distributed and the sixth largest genus in the angiosperms (Hughes et al. 2015–onwards; Moonlight et al. 2018), Begonia L. consists of 2007 known species belonging to 70 sections (Hughes et al. 2015–onwards; Moonlight et al. 2018) . Although showing a very high diversity in the specific level, the classification and phylogeny of this mega genus remain uncertain due to inadequate field surveys, high similarity and variation in morphology, and wild hybridization (Moonlight et al. 2018; Tian et al. 2018a). Begonia species are commonly sensitive to the environment, particularly with a low tolerance to both high and low temperature and strong sunlight. In addition, due to their high ornamental and medicinal values, some wild begonias have been commercially over-collected (Tian et al. 2018a). The vulnerability of the restricted distribution and the fact that it is easily disturbed by human activities has resulted in many Begonia species becoming endangered (Shui and Chen 2018).

In the past 20 years, the recognized Begonia species increased from 80 to 200 in China (Tian et al. 2018b). Over 220 species belonging to 10 sections have been illustrated in China, which is one of the diversity centers of Asian begonias. China plays a more and more significant role in classical taxonomy, phylogeny, utilization, and diversity conservation of Begonia (Tian et al. 2018a, 2018b).

In China, the reported Begonia taxa are mainly distributed in southeastern Yunnan and southwestern Guangxi. Over 90 species have been described from Guangxi, most of which belong to B. sect. Coelocentrum (Gu et al. 2007; Dong and Liu 2018). We conducted field surveys in several places in southwestern Guangxi on April 1, 2015, November 13, 2016, and in October 2019, respectively and found a putative new Begonia species similar to B. edulis H.Lév. and B. dielsiana E.Pritz. ex Diels in morphology. In October 2020, the type specimens with flowers were collected from Shiwanshan Mountain. Based on further detailed morphological observation and comparison with its allied species and molecular phylogenetic evidence, the species is confirmed as a new one belonging to B. sect. Platycentrum (Klotzsch) A.DC.

Begonia pseudoedulis is assigned to B. sect. Platycentrum by its 2-loculed ovary, placentation axile, and placentae bifid per locule (Gu et al. 2007). In the same section, it is most similar to B. edulis and B. dielsiana and B. emeiensis in morphology (Fig. 4).

The new species shows high resemblance to B. edulis in stout creeping rhizome, erect stem at anthesis, palmate veins, chartaceous leaf blade, dichasial cyme, unequally 3-winged capsule (Table 2, Fig. 6; Gu et al. 2007). However, it can be distinguished from B. edulis mainly by its densely red hirsute (gradually wide down to base) (vs. glabrous to subglabrous) petioles and red hispid (vs. glabrous or nearly so) on the abaxial surface of outer tepals of staminate flowers, ovary and fruits, and usually variegated and seldom pure green (vs. evenly green or dark green) leaf blades.

Figure 6. 

B. edulis (A–J) and B. dielsiana (K–O) for comparison to B. pseudoedulis A habitat B, C leaf blade (adaxial and abaxial) D inflorescence E staminate flower F, G pistillate flowers H ovary & stigma I cross-section of ovary J immature capsule K habitat L staminate flowers M androecium N pistillate flowers O cross-section of ovary.

B. emeiensis shares almost the same morphologic characters and geographic distribution (Central China) with B. dielsiana and could be treated as a synonym or variety of B. dielsiana based on the unpublished data from Daike Tian’s lab. They can be easily distinguished from the new species in having evenly green leaves with glabrous to subglabrous petioles, glabrous flower tepals, and usually six (less in five) tepals of the pistillate flowers (Table 2, Fig. 6).

Among these three species, B. edulis is most commonly seen in China usually with large populations, and has the widest distribution followed by B. dielsiana. The new species has the narrowest distribution range, which is only found in Guangxi. Although the three species share high similarity in morphology, the molecular evidence strongly supported that they are three different taxa.

This study was supported by the Dongguan Science and Technology of Social Development Program (2020507101165; 2016108101018; 2014108101046), the National Natural Science Foundation of China (31570199), the Guangdong Rural Revitalization Strategic Foundation (20211800400111), the Natural Science Foundation of Guangdong Province, and the Guangzhou Science and Technology Program (201903010076). Special thanks are given to Mr. Jun Liu from Zhejiang University and Mr. Chen-Yang Zhao from Daxin County of Guangxi, for providing photos, and to Ya-Hong Gao from Hangzhou Botanical Garden for providing living plants introduced from Wuming County of Guangxi. We are also grateful to the editor and the reviewers for reviewing our manuscript.