Begoniapseudoedulis, a new species in Begoniasect.Platycentrum (Begoniaceae) from southern Guangxi of China

Abstract Begoniapseudoedulis, a new species in Begoniasect.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.


Introduction
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 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(Tian et al. , 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.

Taxonomic observation
The morphological traits were observed and recorded both in the field and from specimens. The photographs were taken during field surveys in southern Guangxi in China. The specimens are deposited at Chenshan Herbarium (CSH) of Shanghai Chenshan Botanical Garden and Herbarium of Sun Yat-sen University (SYS), respectively.

DNA sequencing and molecular analysis
The 16 species from sect. Platycentrum and 9 species from other sections of Begonia native to mainland China were selected to reconstruct the phylogenetic relationships (Table 1).  B. dregei Otto & A.Dietr. of sect. Augustia (Klotzsch) A.DC. from South Africa was used as outgroup in the phylogenetic analysis. The methods for DNA extraction, amplification and data analysis were adopted from Tian et al. (2014Tian et al. ( , 2015. The nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) region was amplified with primers from Chung et al. (2014). The PCR products of ITS were directly sent to Tsingke Biotechnology Co., Ltd. (Shanghai, China) to be sequenced. The phylogenetic analysis of Bayesian inference (BI) was performed in MrBayes v3.2.7 (Ronquist et al. 2012). The GTR+G model was chosen as the optimal model of nucleotide substitution using the Akaike information criterion (AIC; Burnham and Anderson 2002) as implemented in IQ-TREE (Trifinopoulos et al. 2016). The Markov chains were run for 1,000,000 generations and sampled at each 100 generations, with the first 25% discarded as burn-in. Diagnosis. The new species shows high resemblance to both B. edulis and B. dielsiana from the same section (sect. Platycentrum) in their stout and creeping rhizome, erect stem at anthesis, asymmetric ovate and chartaceous leaf blade, palmate venation, dichasial cyme, four tepals of staminate flowers, unequally 3-winged capsules. However, it differs from the latter two mainly by its shorter (vs. taller) plants, variation (variegated more than pure green vs. green or dark-green for B. edulis and pure green for B. dielsiana) in leaf color, hairy (vs. glabrous or nearly so) petioles and red hairs (vs. glabrous or nearly so) on abaxial surface of outer tepals, stable five (vs. usually five and rarely six for B. edulis, and more six than five for B. dielsiana) tepals of pistillate flowers.
Phenology. Flowering August-October, fruiting September-November. Etymology. The specific epithet "pseudoedulis" refers to its similarity to B. edulis, because both are easily confused based on appearance when the inflorescences and flowers are invisible.
Conservation status. Only four populations with under 1000 estimated individuals have been found so far in three counties of Guangxi. Each population consisting of approximately 20-300 individuals is distributed in no more than 200 m 2 area. The

Molecular Analysis
The ITS data set containing 40 accessions represented 26 species, four main sections of Begonia in China and one section from Africa (Table 1). The aligned matrix of ITS region was 664 bp. The result of Bayesian inference analysis was shown in Fig. 5. The sect. Platycentrum appeared monophyletic with a high Bayesian posterior probability (bpp = 0.97). The putative new species was a monophyletic lineage (bpp = 1) and sister with B. dielsiana and B. emeiensis. Begonia edulis with the highest morphologic resemblance of B. pseudoedulis formed another clade.
Nodes with bpp < 0.50 have been collapsed. Sectional placement of taxa is indicated by the following abbreviations: Aug: Augustia, Coe: Coelocentrum, Dip: Diploclinium, Pla: Platycentrum, Rei: Reichenheimia. The numbers after the species names indicate different populations. The samples of new species are indicated in bold letters.

Discussion
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.
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.