Taxonomic reconsideration of Prunusveitchii (Rosaceae)

Abstract Prunusveitchii was published in 1912 and was treated as a synonym of P.serrulatavar.pubescens. The information about this taxon is relatively scarce. When consulting specimens of Prunus L., type materials of Prunusveitchii were found to belong to three taxa and P.veitchii, P.concinna, P.japonicavar.zhejiangensis, C.jingningensis and C.xueluoensis were found to be conspecific. The taxonomic status of P.veitchii is reconsidered in the present paper. Morphometric analyses were performed to evaluate the significance of differences between P.veitchii and P.serrulatavar.pubescens. The results show that the leaves of P.veitchii are significantly smaller and narrower than the leaves of P.serrulatavar.pubescens and the peduncle and pedicels are shorter. According to the results of morphometric analyses, P.veitchii should be treated as a separate species. To address these results, a lectotype of P.veitchii is designated here and P.concinna, Cerasusjingningensis and C.xueluoensis are here designated as synonyms of P.veitchii.


Introduction
Cerasus A. Gray, the taxon that includes species commonly known as cherries, is a group that is famous for germplasm resources of edible fruits and flowering trees and shrubs. Historically, Cerasus has been treated either as a subgenus of Prunus L. or as a separate genus (Wen et al. 2008). In the past twenty years, molecular phylogenetic analyses (Bortiri et al. 2001;Lee and Wen 2001;Wen et al. 2008;Shi et al. 2013;Chin et al. 2014) have supported recognition of Prunus sensu lato, including Cerasus, as a single genus and have also shown that, with the removal of the species in sect. Microcerasus, a monophyletic Cerasus can be recognised. Although the inclusion of Cerasus within Prunus is no longer as controversial as it used to be, there are still many problems with the taxonomy of this clade (Wu et al. 2018).
Prunus veitchii Koehne (Koehne 1912) is a species of shrub cherry that occurs at altitudes above 1000 m in western Hubei Province, China. It was treated as a synonym of P. serrulata var. pubescens Wilson by Wilson (1916), a treatment followed by "Flora Reipublicae Popularis Sinicae" (Yü and Li 1986) and "Flora of China" (Li and Bartholomew 2003) and also by Koehne (1917), albeit with reservation. We found that the type materials of P. veitchii actually belonged to three taxa and that the voucher of Wilson's treatment is not the same plant as the specimen on which Koehne's description was based. This means that the taxonomic status of P. veitchii needs to be redefined.
Meanwhile, we also found that P. veitchii, P. concinna, P. japonica var. zhejiangensis, Cerasus jingningensis and C. xueluoensis should all be conspecific due to their similarities in morphology and habitat. The histories of all of these taxa are relevant and are described below.
First, along with the publication of P. veitchii, Koehne (1912) described another shrub cherry, P. concinna, from a similar habitat. Due to the lack of materials, Koehne was uncertain about its status and the name is still unresolved today. Second, Chang (1992) described P. japonica var. zhejiangensis based on Zhang Fanggang & Li Zhiyun 5309, which was collected from southern Zhejiang Province. This variety (Figure 1) was thought to be different from the typical variety in its persistent ovate stipules and black fruit (Chang 1992). However, it is strange that Chang did not include this variety in "Flora of Zhejiang" (Editorial Board 1993), which was published in the following year and for which Chang was involved in compiling most of the content for Rosaceae, including Prunus L. Although the taxon was later included in "Flora of China" (Li and Bartholomew 2003), it was overlooked in later publications , Yan et al. 2017. Third, Xu et al. (2012) described a new species of cherry, C. jingningensis ( Fig. 1), based on specimens collected from southern Zhejiang Province. Recently, P. japonica var. zhejiangensis was treated as a synonym of C. jingningensis by Liu et al. (2017). Finally, C. xueluoensis was published by Nan et al. (2013) based on Cheng-Hui Nan 040301, which was collected from western Hubei Province.
Here, we use morphometric analyses to test the distinct nature of P. veitchii and P. serrulata var. pubescens and conclude that the former should be recognised as a separate species. We designate a lectotype for P. veitchii and reduce P. concinna, Cerasus jingningensis and C. xueluoensis to its synonymy. To evaluate the differences between P. veitchii and P. serrulata var. pubescens, specimens from different origins were selected to gather morphological data and which were subjected to morphometric analyses. Seven floral characters and eight leaf characters (Table 1) were selected for analyses, following Chang et al. (2007), though some characters used by Chang et al. (2007) were discarded because it was not possible to collect enough relevant data from the available specimens. A total of 26 specimens for floral characters and 44 specimens for vegetative characters were measured (see Appendix 1). Measurements were made manually with rulers for borrowed specimens or performed using Digimizer version 4.6.0 (MedCalc Software 2018) for online images.

Herbarium specimens from
A non-parametric Kruskal-Wallis ANOVA was conducted to evaluate the significance of the difference in measured characters between P. veitchii and P. serrulata var. pubescens in each character, as not all characters follow a normal distribution. Box plots were created to illustrate the differences. Data analyses were performed in R version 3.5.1 (R Core Team 2011) and diagrams were created by using ggplot2 package (Wickham 2016).

Results
After examining the type specimens, other collections, relevant literature and plants in the field, we determined that P. veitchii, P. concinna, P. japonica var. zhejiangensis, C. jingningensis and C. xueluoensis must be conspecific. Their original descriptions are not essentially different (Table 2). Although the type specimens of these taxa cannot all be compared directly because they were collected in different seasons and stages of development, it was clear that they are conspecific after consulting specimens collected from the type localities in different seasons. The result of basic statistics and Kruskal-Wallis ANOVA are summarised in Table 3. The box plots ( Figure 2) show that there is no significant overlap between P. veitchii and P. serrulata var. pubescens for most of the measured characters. Moreover, ANOVA showed that the means of almost all measured characters differ significantly, except width of the calyx lobes.

Discussion
Prunus veitchii was treated as a synonym of P. serrulata var. pubescens by Wilson, a treatment that was followed by Koehne with reservation (Koehne 1917). Koehne (1917) mentioned that the sepals of P. veitchii are ovate and shorter and the leaflets are smaller than those of P. serrulata var. pubescens. Consistent with Koehne's observation, our morphometric analyses show that the leaves of P. veitchii are smaller, while the sepals are shorter and wider. The leaves of P. veitchii are also obviously narrower than the leaves of P. serrulata var. pubscens, while the calyx tubes are longer and the peduncles and pedicels are shorter. These results indicate that P. veitchii should not be treated as a synonym of P. serrulata var. pubescens.
The short peduncle was thought to be an important feature that distinguished P. sargentii Rehder from members of the P. serrulata complex (Chang et al. 2007). According to the key to classify the P. serrulata complex and its related species published by Chang et al. (2007), P. veitchii is similar to P. sargentii, having an umbellate or subumbellate inflorescence, sessile or short-pedunculate, consisting of 1-4 flowers with tubular hypanthia, triangular-lanceolate sepals with entire margins and white to reddish petals. Nonetheless, P. veitchii is definitely different from P. sargentii, which has small and elliptic or obovate-elliptic shaped leaves and short petioles, as opposed to the leaves of P. sargentii are elliptic-obovate or oblong-obovate and the length of leaves and petioles can reach 12 cm and 3 cm long (Rehder 1940). In addition, the distribution of P. veitchii is significantly different from that of P. sargentii. The former is mainly distributed around central and eastern China, while the latter is mainly distributed in northern Japan, the Korean peninsula and far eastern Russia (Chang et al. 2007). Therefore, we think that it is better treated as an separate species, based on current evidence.  (Koehne 1912) in the original literature and Rehder's description (Rehder 1940 E. H. Wilson 66 (Veitch Expedition) collected in April 1900, was cited as the voucher when Koehne described P. veitchii. However, this collection number is a source of some confusion. Number "66" was re-used by Wilson for a specimen collected in 1907 during his expedition for Arnold Arboretum, which was determined by Koehne (1912) as a certain form of P. triflora. Another number "66a", also collected in April 1900, was cited as P. tenuiflora by Koehne in "Plantae Wilsonianae" (Koehne 1912). There are 7 sheets (Table 4) designated as Wilson 66, collected in April 1900, in the Global Plant database (JSTOR 2018), three of which are not congruent with the original description. Amongst these three specimens, one of them, A00241703, contains Wilson's handwriting, which says 'Prunus serrulata var. pubescens', indicating it is the voucher for Wilson's treatment of P. veitchii as a synonym of P. serrulata var. pubescens. It is reasonable to infer that the mixed collection led Wilson to propose a taxonomic treatment, different from Koehne.
As for why this species was published again several times, we believe that there are several reasons besides the confusing voucher. First, the vouchers of this species are deposited in different herbaria in different countries, so it would have been dif- ficult to consult all of them in the past. Second, few sources, especially those easily accessible to Chinese plant taxonomists, record this species. P. veitchii is not included in "Flora Hubeiensis" (Fu 2002) and it is listed as one of the synonyms of P. serrulata var. pubescens in "Flora Reipublicae Popularis Sinicae" (Yü and Li 1986) and "Flora of China" (Li and Bartholomew 2003), which makes it easy to be ignored. And neither "Flora Hubeiensis" (Fu 2002) nor "Reipublicae Popularis Sinicae" (Yü and Li 1986) record P. concinna, which is only listed as a species that could not be treated in "Flora of China" (Li and Bartholomew 2003) because the authors had not seen the type specimens. Third, this species sometimes has three winter buds growing side by side, which has led some authors to treat it mistakenly as a member of section Microcerasus (Nan et al. 2013, Liu et al. 2017). However, this trait is quite unstable. From observations of herbarium specimens and plants in the field, we found that the number of buds varies from one to three or four and mostly only one bud can be found (Figure 3).
According to the International Code of Nomenclature (ICN) (McNeill et al. 2012), it is necessary to designate a lectotype of P. veitchii, since the voucher points to more than one taxon. We choose the barcoded sheet US00130697 as the lectotype, since a label with Koehne's handwriting, 'Prunus veitchii Koehne' is affixed to it. Table 3. Arithmetic average ±standard deviation and Kruskal-Wallis ANOVA for measured morphological characters. A, Peduncle length (cm). B, Pedicel length (cm). C, Length of calyx tube (cm). D, Diameter of calyx tube top (cm). E, Length of calyx lobe (cm). F, Width of calyx lobe (cm). G, Ratio of length and width of calyx lobe. H, Petiole length (cm). I, Leaf length (cm). J, Leaf width (cm). K, Angle of leaf base (°). L, Angle of leaf apex (°). M, Length of leaf apex (cm). N, Ratio of leaf length and petiole length. O, Ratio of length and width of leaf.