﻿A new species of Sedum (Crassulaceae) from Mount Danxia in Guangdong, China

﻿Abstract Sedumjinglanii, a new species of Crassulaceae from Mount Danxia in Guangdong, China, is described and illustrated. Phylogenetic analysis based on the internal transcribed spacer (ITS) region of nrDNA suggests that the new species belongs to S.sect.Sedum sensu Fu and Ohba (2001) in the “Flora of China”, and is sister to a clade comprising S.alfredi and S.emarginatum with high support values (SH-aLRT = 84, UFBS = 95) but is distantly related to S.baileyi. The new species is morphologically similar to S.alfredi but it can be distinguished from the latter in its opposite leaves (vs. alternate leaves), its usually wider leaves (0.4–1.2 cm vs. 0.2–0.6 cm), its usually shorter petals (3.4–4.5 mm vs. 4–6 mm), its shorter nectar scales (0.4–0.5 mm vs. 0.5–1 mm), its shorter carpels (1.5–2.6 mm vs. 4–5 mm), and its shorter styles (0.6–0.9 mm vs. 1–2 mm). The new species can be easily distinguished from S.emarginatum which both have opposite leaves by its short, erect or ascending rhizome (vs. long and prostrate rhizome in the latter), shorter petals (3.4–4.5 mm vs. 6–8 mm) and shorter carpels (1.5–2.6 mm vs. 4–5 mm). It can also be easily distinguished from S.baileyi by its short, erect or ascending rhizome (vs. long and prostrate rhizome) and its shorter style (0.6–0.9 mm vs. 1–1.5 mm).


Introduction
According to Fu and Ohba (2001) in the "Flora of China", Sedum Linnaeus is the most species-rich genus of the family Crassulaceae, comprising about 470 species. However, as presently circumscribed, the genus is highly polyphyletic, and a monophyletic circumscribed genus Sedum s.l. would comprise approximately 755 species by inclusion of all 14 genera currently recognized in tribe Sedeae into it (Messerschmid et al. 2020). The genus is distributed in temperate and subtropical environments, and the diversity center is in the Mediterranean Sea, Central America, the Himalayas and East Asia (Stephenson 1994;Thiede and Eggli 2007). In China, 121 Sedum species are documented, amongst which 91 species are endemic (Fu and Ohba 2001).
Molecular data unambiguously demonstrate the polyphyletic nature of Sedum with its species placed in four major crown clades of the crassulacean tree, for example, Acre, Aeonium, Leucosedum, and Sempervivum. There is no agreement between specialists regarding the infrageneric structure of Sedum (reviewed in Nikulin et al. 2016). According to Fu and Ohba (2001), Chinese Sedum are divided into three sections, including S. sect. Sedum, S. sect. Oreades (Fröderström) K.T. Fu, and S. sect. Filipes (Fröderström) S.H. Fu. S. sect. Sedum is distinguishable from the two latter sections by the adaxially gibbous carpels and follicles, while S. sect. Oreades differs from S. sect. Filipes in the spurred leaf base and yellow petals (vs. spurless leaf base and white or reddish-purple petals) (Fu and Ohba 2001). During our investigations in Danxiashan National Park, Guangdong Province, China, an unknown Sedum species with opposite leaves was collected. After several years of field observations, comprehensive literature studies and molecular analysis, we confirmed that it was a new species and it is described and illustrated here.

Materials and method
Field investigations and observations were conducted during the flowering and fruiting periods of the putative new species. We obtained morphological data of this putative species by measurements based on 6-8 living samples. Mean values of these statistical data were calculated and then were compared with six other related species (Table 2). The specimens were collected in Danxiashan National Park, Renhua County, Guangdong Province, China. Voucher specimens were deposited in the herbarium of Sun Yat-sen University (SYS).
Two representative individuals from different populations were selected for further molecular experiments, one from Bazhai of Mount Danxia (Y. S. Huang 21040301) and another one from Yanyan of Mount Danxia (Q. Fan et al. DNPC 2873). Fresh leaves of the two individuals were collected and stored with silica gel in zip-lock plastic bags until use. Total DNA was extracted using the modified CTAB method (Doyle and Doyle 1987). The region of the partial internal transcribed spacer 1, 5.8S ribosomal RNA gene and partial internal transcribed spacer 2 was amplified using previously reported primers ITS1 and ITS4 (White et al. 1990). PCR amplifications were performed following Huang et al. (2021).
In order to explore the phylogenetic position of the putative new species in Sedum, ITS sequences of 56 accessions representing 46 Sedum taxa and three outgroup species (Aeonium lancerottense, Aeonium viscatum, and Greenovia aizoon) were downloaded from the Genbank public database at the National Center for Biotechnology Information (NCBI) ( Table 1). The sequences were aligned using ClustalW 1.8 (Thompson et al. 1994) and then adjusted manually. Besides, to improve the credibility, we also aligned the sequences using MAFFT v.7.402 (Katoh and Standley 2013), and the alignments generated from the two methods were consistent. The best-fit nucleotide substitution model was determined by ModelFinder (Kalyaanamoorthy et al. 2017). Based on the maximum likelihood (ML) method, the phylogenetic tree was constructed using IQ-Tree v. 2.0.3 (Nguyen et al. 2015) by executing 5,000 replicates of SH approximate likelihood ratio test (SH-aLRT) and ultrafast bootstrap (UFBS) (Hoang et al. 2018). Finally, the tree file was visualized by the online tool of Interactive Tree Of Life (iTOL) v5 (Letunic and Bork 2021).

Results and discussion
The alignment length of the ITS sequences was 624 bp, amongst which 340 were parsimony-informative. Within the new species, only one variable site was detected, but 40 variable sites were detected between the new species and S. alfredi and 40 variable sites were detected between the new species and S. emarginatum, indicating that pronounced genetic differentiation existed between the new species and S. alfredi as well as S. emarginatum. The best-fit nucleotide substitution model was estimated as SYM+I+G4 according to the Bayesian Information Criterion (BIC).
As the ML phylogenetic tree shows ( Fig. 1), seven subclades were resolved with moderate to high support values. Accessions of the putative new species, S. alfredi, S. emarginatum, and S. lungtsuanense together formed subclade 7 with high support values (SH-aLRT = 92, UFBS = 98), all belonging to S. sect. Sedum sensu Fu and Ohba (2001). Morphologically, the putative new species is similar to S. alfredi from which it can be easily distinguished by its opposite leaves (vs. alternate leaves in the latter). Furthermore, the leaves of the putative new species are usually wider than those of S. alfredi (0.4-1.2 mm vs. 0.2-0.6 mm), the petals are usually shorter (3.4-4.5 mm vs. 4-6 mm), the nectar scales shorter (0.4-0.5 mm vs. 0.5-1 mm), the carpels shorter (1.5-2.6 mm vs. 4-5 mm) and the styles shorter (0.6-0.9 mm vs. 1-2 mm) ( Table 2). Phylogenetically, the putative new species is closely related to S. emarginatum. Although the leaves of both species are opposite, it can be easily distinguished from the latter by its short, erect or ascending rhizome (vs. long and prostrate rhizome), shorter petals (3.4-4.5 mm vs. 6-8 mm) and shorter carpels (1.5-2.6 mm vs. 4-5 mm). The putative new species was distantly related to S. baileyi in the phylogenetic tree although both are morphologically similar (Table 2). Also, it can be easily distinguished from the latter by its short, erect or ascending rhizome (vs. long and prostrate rhizome) and its shorter style (0.6-0.9 mm vs. 1-1.5 mm).
Through numerous scientific investigations, more than a dozen new species were found on Mount Danxia in Guangdong in recent years, and most are endemic to it such as Lespedeza danxiaensis Q.Fan, W.Y.Zhao & K.W.Jiang (Zhao et al. 2021), Asplenium danxiaense K.W.Xu (Xu et al. 2022 (Figs 2, 3).
Phenology. Flowering from April to May. Fruiting from June to August. Etymology. Sedum jinglanii is named after Prof. Jing-Lan Feng (1898-1976, an academician of the Chinese Academy of Sciences and one of the founders of mineralogy in China. In 1928, he discovered and named the red beds and related strata in North Guangdong as "Danxia Formation" for the first time (Peng 2020).