﻿Commelinadanxiaensis (Commelinaceae), a new species from Guangdong, China

﻿Abstract Commelinadanxiaensis (Commelinaceae), a remarkable new species from Mount Danxia, Guangdong Province, China, is described and illustrated. This species is similar to C.communis in inflorescences and flowers but readily distinguishable in its nearly erect stems, larger flowers, and different petal colouration.


Introduction
Commelina L. is the largest genus of Commelinaceae, consisting of about 170 species distributed in tropical and subtropical regions (Faden 1998(Faden , 2012, with eight species recorded for China (Hong 1997;Hong and DeFilipps 2000). The genus is most diverse in tropical Africa, where an estimated 100 species occur (Faden 2001), with a wide range of variation in habit, inflorescence, flower colour, capsule dehiscence, seed number, testa ornamentation, and chromosome number (Faden 2012). Most of its species occur in open environments or as weeds along roadsides or in cultivation fields, but a few of them are restricted or exclusively known from forest habitats (Faden 2012;Nandikar 2013;Nandikar and Gurav 2014). Commelina is easily differentiated from the remaining genera in the tribe by its inflorescences which are subtended by spathaceous basal bracts and reduced to (1-)2 fasciculate cincinni, zygomorphic flowers, petals clawed, unequal and mostly blue (but sometimes white or lilac, rarely yellow, apricot or orange), three posterior staminodes with 6-lobed cruciform antherodes, three anterior stamens, and 2-locular or unequally 3-locular and 2-valved capsules (Faden 1998;Pellegrini and Forzza 2017).
During our botanical investigation of Mount Danxia of Guangdong Province in 2019-2020, we found an unusual population of Commelina. The plants are most closely similar to C. communis L., a species widely distributed in Asia, but differ mainly by the ascending stems (vs. creeping), petals sky-blue with a white basal third (vs. evenly dark blue).

Materials and methods
Morphological observations of the putative new species and its close relatives were carried out based on living plants in the field, as well as on dried specimens. The voucher specimens were deposited in the Herbarium of Sun Yat-sen University (SYS). Leaf samples for the putative new species were collected and stored in silica gel. Total DNA was extracted from dried leaves using the modified CTAB method following the protocol of Doyle and Doyle (1990). In order to clarify the taxonomic delimitations of the putative new species and its relative species, sequences from one nuclear gene (nrITS) and three chloroplast DNA regions (matK, rbcL and trnH-psbA) were used respectively to estimate a Maximum Likelihood phylogeny tree. Some species belonging to genera of tribe Commelineae, which were related to Commelina (Faden, 1991), have been chosen as outgroups, such as Floscopa scandens Lour., Murdannia edulis (Stokes) Faden, and M. bracteata (C.B.Clarke) Kuntze ex J.K.Morton, sequences of which were downloaded from Genbank. Details of sequence data are given in Appendix 1.
The multiple sequences of each gene were aligned with Clustal X (Thompson et al. 1997) and then manually adjusted in Sequence Alignment Editor (Rambaut 2002). Gaps within the sequence were treated as missing data. The whole dataset was analysed with Maximum Likelihood (ML) methods. Clade support was estimated using 1,000 bootstrap replicates (BS) with the same heuristic search conditions. The ML analyses were performed with RAxML v.8.2.4 (Stamatakis 2014).

Molecular analyses
The ML phylogenetic tree based on nrITS ( Fig. 1) showed that all seven Commelina species were clustered into one lineage. Three individuals of Commelina danxiaensis were recovered in a clade sister to a clade composed of C. africana, C. benghalensis, C. erecta, C. diffusa, and C. paludosa. Ten individuals of C. communis are recovered in a poorly supported clade, distantly related to C. danxiaensis. The ML phylogenetic tree based on three chloroplast DNA regions (matK, rbcL, and trnH-psbA) (Fig. 2) showed that all seven Commelina species were clustered into one lineage, and the outgroups were clustered into another one. And the two individuals of C. danxiaensis clustered into one lineage and were sistered to the lineage clustered with C. communis and C. paludosa. Although the phylogenetic trees based on nrITS and chloroplast DNA were in conformity, the individuals of C. danxiaensis formed one lineage, which partly supported it as a distinct species.  Diagnosis. Commelina danxiaensis is morphologically similar to C. communis due to their diffuse stems, lanceolate leaf-blades and approximate floral forms. However, it differs in its ascending stems (Fig. 4B), tomentose leaf-blades and sheaths ( Fig. 4C-F), and sky-blue lateral petals with a white basal third (Fig. 4G).
Phenology. Commelina danxiaensis flowers from April to July and fruits from June to September.
Distribution and habitat. Commelina danxiaensis is only known from the type locality, Mount Danxia, Renhua County, Guangdong Province, China. Only two populations have been found, with several hundred individuals. It grows on dry mountaintops of the Danxia formation at elevations of 100-350 m.
Conservation assessment. Commelina danxiaensis has only been found in Mount Danxia within an area of less than 20 km 2 , making it putatively 'Vulnerable' (VU D2) according to the guidelines of the IUCN Red List Categories and Criteria (IUCN 2022). However, the threat risk seems low because it is not economically valuable, and the area's conservation is good.
Discussion. The new species Commelina danxiaensis is similar to C. communis and C. diffusa in some of its morphological characters, such as lanceolate leaf-blades, cordate spathes free at base, and blue paired petals. Morphological comparisons among them have been listed in Table 1.
Additionally, we found the name Commelina bicolor D.Q.Wang & M.E.Cheng described by Wang et al. (2019), which is a later homonym of C. bicolor Poepp. ex Kunth (1843). Therefore, it is illegitimate under Art. 53.1 of ICN (Turland et al. 2018). This species is documented in Anhui and Hubei Provinces, and the type speci-  (Wang et al. 2019). We previously believed the unknown species of Commelina in Mount Danxia to be conspecific with C. bicolor due to its similar morphological and ecological characteristics and treated it as a new distribution record for the Guangdong flora (Dai et al. 2021). However, we have been unable to check the type material at PE, where the authors stated the holotype specimen was deposited, to confirm the plant's identity and the name's application. We carried out fieldwork at Daqian Shan but were unable to find any individuals of this species. Hence, treatment has not been made for this species at the moment. It is planned that a further study will be carried out in the future. Up to the present time, four species of Commelina have been documented in Danxiashan National Nature Reserve, including the new species Commelina danxiaensis. In order to facilitate identification, we here provide a key and checklist for the Commelina species in Mount Danxia.