Geum sunhangii – first discovered in Shennongjia National Nature Reserve, Hubei Province, China – is described as a new species of Rosaceae. Compared to all known Chinese Geum species, the new species differs by possessing jointed styles, imbricate petals and a reniform radical leaf terminal leaflet. Most significantly, the jointed style is curved at an obtuse or a right angle. In addition, the inclusion of this species within the genus Geum was supported by phylogenetic analysis using the sequence data of a nuclear ribosomal internal transcribed spacer (nrITS) and a chloroplast trnL–trnF intergenic spacer. The new species was found to be closely related to G. rivale and G. aleppicum.

anatomical, morphology, phylogeny, taxonomy

The genus Geum L. (1753: 500) (Rosaceae), also known as Avens, contains ca. 56 species distributed throughout the temperate, tropical and arctic regions of the world and is found mainly in the Northern Hemisphere (Gajewski 1959). The morphology of Geum is very complex. Most species are herbaceous perennials that form rosettes consisting of imparipinnate leaves and a thick caudex, but a few species are small shrubs. In addition, most species in this genus have fish-hook shaped fruits (Rafinesque 1833). Only three species G. aleppicum Jacq., G. rivale L. and G. japonicum var. chinense F.Bolle are present in China (Li et al. 2003). Bolle (1933) divided Geum into several genera, including Novosieversia F.Bolle and Oncostylus F.Bolle (Bolle, 1933), amongst others. However, based on cytological data, Gajewski (1957) concluded that Geum is a polyploid complex and did not support any previous circumscriptions of Geum; instead, Gajewski recognised most of the previously segregate genera as subgenera within the genus Geum (Gajewski 1957, 1968). Finally, his point of view was further supported by later morphological and molecular studies (Schulze-Menz 1964; Hutchinson 1967; Robertson 1974; Kalkman 1988; Smedmark and Eriksson 2002).

The Shennongjia National Nature Reserve is located in the northwest of China’s Hubei Province. It is a world diversity hotspot defined by its unique geographical location and complex topography (Hu et al. 2004). The Nature Reserve is also characterised by its high species diversity (including many rare and endangered animals and plants) and relict plant species (Fan et al. 2017). Correspondingly, it has recently attracted considerable attention from many researchers (Ma 2016; Xie et al. 2017). Recently, several new angiosperm taxa have been discovered there, including Zhengyia shennongensis T. Deng, D.G. Zhang & H. Sun (Deng et al. 2013), Mazus sunhangii D.G. Zhang & T. Deng (Deng et al. 2016) and Impatiens baokangensis Q.L. Gan & X.W. Li (Gan and Li 2016).

During a biodiversity survey of the Shennongjia National Nature Reserve, we discovered an undescribed species belonging to the Rosaceae. This species was distinguished by the presence of a rosette of basal leaves, petals and jointed styles. Our morphological and molecular studies revealed that the newly-collected material belongs to an unknown Geum species which is described here.

Plant materials. Specimens of the new species were collected from a site in Shennongjia National Nature Reserve, Hubei Province. Leaves of the new species were obtained for molecular studies. All herbaria used in this study were obtained from KUN (Herbarium, Kunming Institute of Botany, CAS).

Anatomical observation. Specimens of G. sunhangii were dissected and directly observed, before being placed under an anatomical lens for further observation under magnification. The cauline leaf, radical leaves, seeds, petal, style joint and stamen were inspected.

DNA sequencing and molecular analyses. Total DNA was extracted using a DP305 Plant Genomic DNA Kit (Tiangen, Beijing, China) and we selectively amplified the nuclear ribosomal internal transcribed spacer (nrITS) and chloroplast trnL–trnF intergenic spacer (trnL–trnF) regions by Polymerase Chain Reaction (PCR). Successfully amplified DNA fragments were then sequenced commercially. Molecular analysis was performed using two outgroups (i.e. Fallugia paradoxa Endl. and Sanguisorba officinalis L.; Potter et al. 2007), one piece of material from the putative new species and fourteen samples with similar morphology. Partial sequences were obtained from GenBank (https://www.ncbi.nlm.nih.gov/genbank); GenBank accession numbers for all species are listed in Table 2. Multiple sequence alignments were initially performed using CLUSTAL W ver. 1.4 (Thompson et al. 1994) and were manually adjusted using BioEdit ver. 7.0.5.3 (Hall 1999). We used SequenceMatrix ver. 1.7.8 to combine the sequences (Vaidya et al. 2011).

Phylogenetic trees were constructed using Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI) algorithms. All characters were weighted equally, with gaps treated as missing data. MP analysis was conducted using PAUP ver. 4.0a (Swofford 2002). MP trees were obtained from a heuristic search of 1000 random addition replicates using tree bisection-reconnection (TBR). Finally, we obtained 1000 bootstrap values to evaluate the support for each branch.

ML analyses were conducted using the IQ–TREE web server (http://iqtree.cibiv.univie.ac.at/) (Trifinopoulos et al. 2016). We performed 1000 replicates with the substitution model set to ‘Auto’. Bayesian Inference was performed using Modeltest ver. 3.7 (Posada and Crandall 1998) to determine the best-fit models of nucleotide substitution. A comparison between the Akaike Information Criterion (AIC) values obtained with different tree models using the combined dataset revealed that TIMef was the most appropriate (Posada 2004). However, the best-fit TIMef model was substituted by the GTR + I model because TIMef was not available for further analyses. Bayesian Inference was performed using MrBayes ver. 3.1.2 (Ronquist 2003). The programme was run for 10 million generations and sampling was performed every 1000 generations. Each tree used two independent Markov Chain Monte Carlo (MCMC) (Yang 1997) analyses with four chains. When the average standard deviation of split frequencies was less than 0.01, a consensus tree was calculated after discarding the first 25% of trees as burn-in. A Bayesian tree was constructed from the remaining trees with Posterior Probability (PP) values for each clade.

Geum aleppicum and G. japonicum var. chinense are similar in morphology; they both have similar yellow petals and green sepals, but these species differ in receptacle hair (Fig. 4Aa, Ba; Table 1). In contrast, G. rivale is easily recognisable due to its purplish sepals and purple-brown striped petals (Table 1). The nodding flower of the new species is similar to that of G. rivale. Therefore, the combination of green sepals, nodding flower, yellow and imbricate petals is distinctly different from those found in the other three species present in China. In addition, the radical leaf and style joint of the new species are distinct in this genus. The terminal largest leaflet of the radical leaf is reniform (Fig. 3G) and different from the other species, which possess rhombic-ovate or compressed orbicular leaflets (Table 1). Curved styles are also important and recognisable features of the new species. Obtuse or right-angle curves of the style joint can be used to distinguish between the new species and its close relatives (Figs 3F, 4a). All distinguishing features are shown in Fig. 4 and Table 1.

Figure 3. 

Anatomical characters of Geum sunhangii. A, B Cauline leaf C seeds D stamens E petal F style joints G radical leaf.

Figure 4. 

Morphological comparison of Chinese Geum species. A G. aleppicum B G. japonicum var. chinense C G. sunhangii (infructescences (a), cauline leaves (b) radical leaves (c) and flowers (d)).

We obtained samples of fifteen species for phylogenetic analysis. The topologies of the Bayesian, ML and MP trees were identical and were consistent with previous studies (Smedmark and Eriksson 2002). According to our results, Geum is probably a polyphyletic group and the boundary between Geum and species in Clade II is not clear (Fig. 5). At the same time, species in the genera Taihangia T.T. Yu & C.L. Li, Coluria R.Br. and Waldsteinia Willd. are likely congeneric to the Geum species. Therefore, further studies of the taxonomic and phylogenic relationships of Geum, Taihangia, Coluria and Waldsteinia species are needed. At present, the new species was confirmed as a member of Geum, since G. sunhangii was nested within a group of Geum species (PP = 1, LP = 100%, MP = 100%; Fig. 5) that form a monophyletic group (Fig. 5). In addition, the new species can be easily identified by its morphological features.

Figure 5. 

Bayesian consensus tree of the combined ITS and trnL–trnF sequence dataset. Numbers above branches indicate Bayesian posterior probability [PP], numbers below branches represent maximum likelihood bootstrap [LP] and maximum parsimony bootstrap [BP] values. The dash (–) indicate BP and LP < 50%. The new species is shown in bold. The monophyletic group with high support is framed by the blue rectangle.

Figure 6. 

Distribution of Geum sunhangii in Hubei Province, China. Star indicates the type locality of G. sunhangii.

This study was supported by grants from the National Natural Science Foundation of China (31670206), NSFC-Yunnan joint fund to support key projects (U1802232), Chinese Academy of Sciences (XDA20050203), the National Key R & D Program of China (2017YFC0505200), the Major Program of the National Natural Science Foundation of China (31590823), the National Natural Science Foundation of China (31700165), the Youth Innovation Promotion Association of Chinese Academy of Sciences (2019382), the Young Academic and Technical Leader Raising Foundation of Yunnan Province (2019HB039) and the CAS “Light of West China” Program.