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Research Article
Taxonomic notes on Sorbus megalocarpa (Rosaceae) and related taxa
expand article infoXin Chen‡, JianHui Ma‡, LiYang Geng‡
‡ Nanjing Forestry University, Nanjing, China

Corresponding author: Xin Chen ( chenxinzhou@njfu.edu.cn )

Academic editor: Ali Dönmez
© 2022 Xin Chen, JianHui Ma, LiYang Geng.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Chen X, Ma JH, Geng LY (2022) Taxonomic notes on Sorbus megalocarpa (Rosaceae) and related taxa. PhytoKeys 201: 131-138. https://doi.org/10.3897/phytokeys.201.84027
Open Access

Abstract

Four Sorbus taxa endemic to China, S. arguta, S. guanxianensis, S. megalocarpa var. megalocarpa and S. megalocarpa var. cuneata, are morphologically similar to one another in having large brown fruits with persistent calyx and dense lenticels. In literature, either all of the four taxa were accepted, or two of them, S. arguta and S. megalocarpa var. cuneata, were treated as synonyms of S. megalocarpa var. megalocarpa, or S. guanxianensis alone was dubious. In this study, based on morphological comparison, S. arguta is reinstated for its relatively small inflorescence, small fruit and timing of flowering after leaves are unfolded. S. megalocarpa var. cuneata is confirmed as a synonym and S. guanxianensis is proposed as a new heterotypic synonym of S. megalocarpa.

Keywords

resurrection, Sorbus, synonymization, taxonomy

Introduction

Sorbus L. (1753: 477; Rosaceae) in the broad sense (sensu lato, s.l.) comprises about 100 to more than 250 species mainly distributed in northern temperate regions with the center of diversity in China (Phipps et al. 1990; Lu and Spongberg 2003). Although previous molecular studies indicated that Sorbus s.l. is highly polyphyletic with species falling into six genera: Aria (Pers.) Host, Chamaemespilus Medik. (1879: 138), Cormus Spach, Micromeles Decne. (1874: 168), Sorbus and Torminalis Medik. (1874: 134; Campbell et al. 2007; Li et al. 2012; Lo and Donoghue 2012; Sun et al. 2018; Ulaszewski et al. 2021), the taxonomic diversity of Sorbus in China is being included within a single genus (Yü and Lu 1974; Lu and Spongberg 2003). The number of species native to China recognized varies tremendously according to different taxonomists (Yü and Lu 1974; Phipps et al. 1990; Lu and Spongberg 2003; Aldasoro et al. 2004; McAllister 2005). For example, in the latest revision of Sorbus subg. Aria Persoon and Torminaria (DC.) Reichenbach, Aldasoro et al. (2004) accepted only 21 species out of the total 31 species and 6 varieties recognized by Lu and Spongberg (2003). The striking inconsistencies in taxonomic treatments have given rise to confusion in species identification and utilization. The controversial delimitation of S. megalocarpa Rehder (1915: 266) and its allies, S. megalocarpa var. cuneata Rehder (1915: 267), S. arguta T. T. Yü (Yü and Kuan 1963: 223) and S. guanxianensis Ku (1990: 22), is an example here. The four taxa were all accepted by Yü and Lu (1974), Lu and Spongberg (2003). S. arguta and S. megalocarpa var. cuneata were treated as synonyms of S. megalocarpa and S. guanxianensis was regarded as a doubtful species by Aldasoro et al. (2004). The purpose of this paper is to clarify the taxonomic confusion and to enhance stability of these names based on protologues, related literature studies, original materials examinations and field investigations.

Materials and methods

Type collections and voucher specimens of Sorbus arguta, S. guanxianensis, S. megalocarpa var. megalocarpa and S. megalocarpa var. cuneata were examined from the following herbaria: A, CDBI, E, GH, IBSC, KUN, NF, PE, WCSBG and US (acronyms follow Thiers continuously updated); virtual images were examined mainly through the website PPBC (http://ppbc.iplant.cn/). Morphological comparison presented here is based on analysis of specimens, as well as fresh materials collected by ourselves.

Taxonomic treatments

Sorbus megalocarpa Rehder, Pl. Wilson. 2(2): 266. 1915.

≡ Aria megalocarpa (Rehder) H. Ohashi et Iketani, J. Jap. Bot. 68(6): 359. 1993.

≡ Micromeles megalocarpa (Rehder) Mezhenskyj, NULESU Coll. Fruit Ornament. Pl.: 34. 2018.

≡ Wilsonaria megalocarpa (Rehder) Rushforth, Phytologia 100(4): 241. 2018.

= Sorbus megalocarpa var. cuneata Rehder, Pl. Wilson. 2(2): 267. 1915. Type: CHINA. Sichuan: Western Szechuan, Mupin, 2400–2700 m, 10 October, 1910–11, E.H. Wilson 4215 (lectotype, designated by Aldasoro et al. 2004, pg. 43: K[K000758157]; isolectotype: A[A00112653])

= Aria megalocarpa var. cuneata (Rehder) H. Ohashi et Iketani, J. Jap. Bot. 68(6): 359. 1993.

= Sorbus guanxianensis T.C. Ku, Bull. Bot. Res., Harbin 10(3): 22, f. 2. 1990. syn. nov. Type: China. Sichuan: Guanxian (Dujiangyan), 2000 m, 25 August 1987, T.Z. Fu et al. 872102 (holotype: PE[PE00020830]), syn. nov.

= Micromeles guanxianensis (T.C. Ku) Mezhenskyj, NULESU Coll. Fruit Ornament. Pl.: 34. 2018. syn. nov.

= Wilsonaria guanxianensis (T.C. Ku) Rushforth, Phytologia 100(4): 241. 2018. syn. nov.

Type

China. Sichuan: Western Szechuan, Hung-yah Hsien (Hongyaxian), 1200 m, 12 September 1908, E.H. Wilson 956 (lectotype, designated by Gabrielian 1978, pg. 220: K[K000758158]; isolectotypes: A[A00112650], E[E00147452], GH[GH00112651], US[US00097467]).

Notes

Sorbus megalocarpa : Sorbus megalocarpa was first published by Rehder (1915: 266). It was transferred to genera Aria, Micromeles and Wilsonaria by Ohashi and Iketani (1993: 359), Mezhenskyj (Mezhenska et al. 2018: 34) and Rushforth (2018: 241) respectively.

Three gatherings collected by Wilson under number “956” were cited in the protologue. The first one was collected at alt. 2200–2600 m., Mupin, in October 1910; the second one was collected at alt. 1200 m., Hung-ya Hsien, on September 12, 1908; and the third one was collected at alt. 2000 m., Mon-kong Ting, on June 19, 1908. Since the author did not indicate holotype for the name, the three gatherings are syntypes according to the Article 9.6 of the International Code of Nomenclature for algae, fungi and plants (Shenzhen Code) (Turland et al. 2018). Gabrielian (1978) designated the specimen at K (K000758158; as shown in fig. 1A, plate 62 of Gabrielian 1978), collected from Hung-Ya Hsien, as the lectotype. Four duplicates (A00112650, E00147452, GH00112651, US00097467) out of the eight specimens of “E. H. Wilson 956” traced at A, E, GH, K and US, are the isolectotypes here.

Figure 1. 

Sorbus megalocarpa Rehder A lectotype (K000758158) B an epiphytic plant in the wild (Ya’an, Sichuan, China) C fruit (showing the color of fruit and lenticels on it) D leaves (showing the variation of leaf shape and petiole length in one plant).

Sorbus megalocarpa var. cuneata: Rehder (1915: 267) differentiated Sorbus megalocarpa var. cuneata from S. megalocarpa var. megalocarpa by its “smaller softer fruit” (“fructibus minoribus ovovides circiter 1.5 cm. longis et 1 cm. diam.” and “the more cuneate short-stalked leaves” (“petiolum vix 1 cm”). This variety was recognized by Yü and Lu (1974) and Lu and Spongberg (2003), was transferred to Aria by Ohashi and Iketani (1993: 359) and was treated as a synonym of S. megalocarpa by Aldasoro et al. (2004). The great variability of leaves and fruits of S. megalocarpa was well documented by Aldasoro et al. (2004) and confirmed in our field investigations (Fig. 1B–D). Sorbus megalocarpa has elliptic, elliptic-obovate, obovate-oblong leaves with crenate-serrate margins and petiole of 0.7–2 cm long, and large ovoid, ovoid-globose, or sub-globose fruits (1–2.7 cm long, 0.7–2.2 cm in diameter) covered with dense lenticels. The length of petiole and size of fruits of S. megalocarpa var. cuneata are within the variation range of S. megalocarpa. Therefore, we agree with Aldasoro et al. (2004) in reducing S. megalocarpa var. cuneata to a synonym of S. megalocarpa.

Sorbus guanxianensis : Ku (1990: 22) published Sorbus guanxianensis based on two gatherings, “T. Z. Fu et al 2102” (Fig. 2A) and “Z. L. Zhao 0970”. In the protologue, Ku (1990) included the diagnostic words “calycis lobi mox decidui”, compared it with S. alnifolia (Siebold and Zuccarini) K. Koch in Sorbus sect. Micromeles and differed it by its larger fruits (about 1.5 cm long), though she assigned it to Sorbus sect. Aria (Ku 1990). This contradictory taxonomic description led later authors to treat S. guanxianensis in different circumscriptions. Phipps et al. (1990) and Lu and Spongberg (2003) accepted it. Mezhenska et al. (2018: 34) and Rushforth (2018: 241) also recognized it and transferred it to Micromeles and Wilsonaria respectively. Aldasoro et al. (2004) considered it “a doubtful species” and stated that pomes of S. guanxianensis “without lenticels” and “may by a synonym of S. zahlbruckneri”.

Figure 2. 

A holotype of Sorbus guanxianensis Ku (PE00020830) B holotype of Sorbus arguta T. T. Yu (PE00934274).

No specimens of Sorbus guanxianensis other than the two gatherings cited in the protologue are available in herbarium. Our examination of the type specimens indicated that characters such as persistent calyx and dense lenticels on pomes were in serious conflict with the description in the protologue and were neglected by Aldasoro et al. (2004). Sorbus guanxianensis could easily be distinguished from S. zahlbruckneri C. K. Schneider by the leaves which have margins “singly dentate (not double-dentate)” as stated by Aldasoro et al. (2004) themselves. The unusual characters possessed by the type specimens were noted by Rushforth (2018) who stated that S. guanxianensis “seems to match Rehder’s S. megalocarpa var. cuneata” and transferred it to Wilsonaria together with S. megalocarpa. Morphological similarities (Styles 3 or 4, leaves glabrous or sparsely hair when young, not tomentose, fruit brown, 12–20 mm in diameter, covered in massed contiguous lenticels) stated by Rushforth (2018), and a detailed critical read of the protologues and evaluation of the specimens confirmed that S. guanxianensis is conspecific with S. megalocarpa. Accordingly, we proposed to reduce S. guanxianensis as a heterotypic synonymy of S. megalocarpa here.

Representative specimens examined

China. Sichuan: Baoxin county, 17 July 1925, K.L. Chu 3149 (IBSC); Dayi county, Xiling town, Chadiping, Xiling Snow Mountain, 30°38'24.84"N, 103°09'52.33"E, 1471 m, 1 June 2015, J.D. Ya and X. J. Hu 15CS11089 (KUN); Dujiangyan, Hongkou town, Dashuigou conservation station, 1250 m, D.H. Zhu, C. Zhang, X.J. Li 4872 (WCSBG); Hongya county, forest farm, July 1992, Z.W. Wang A00088 (CDBI); Hongya county, Lewu town, Shuanghekou, 2100–2230 m, 2 August 1959, Z.T. Guan 9120 (PE); Hongya County, Lewu town, Shuanghekou, 2100–2230 m, 3 August 1959, Z.T. Guan 6814 (PE); Leibo county, Mahu town, 1300 m, 25 May 1959, 238 collection team 0338 (PE); Leibo county, Shahezhou forest farm, 2400 m, 12 August 1972, 238 collection team 0697 (PE); Ya’an city, Yingjing county, Longchigou National Forest Park, Daxiangling, 29°36'21.23"N, 102°50'28.48"E, 1364 m, 19 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1891 (NF); Ya’an city, Yingjing county, Longcanggou National Forest Park, Diecuixi, 29°36'55.01"N, 102°53'42.57"E, 1509 m, 19 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1906 (NF); Ya’an city, Yingjing county, Longcanggou National Forest Park, Diecuixi, 29°36'57.42"N, 102°53'38.74"E, 1512 m, 19 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1907 (NF); Ya’an city, Yingjing county, Longcanggou town, Fazhan village, 29°37'04.96"N, 102°53'25.17"E, 1466 m, 20 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1908 (NF); Ya’an city, Yingjing county, Longcanggou town, Fazhan village, 29°38'15.34"N, 102°53'00.64"E, 1359 m, 20 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1914 (NF); Ya’an city, Yingjing county, Longcanggou town, Fazhan village, 29°37'48.37"N, 102°53'13.75"E, 1358 m, 20 September 2020, X. Chen, X.Y. Wang, C.H. Wang 1915 (NF).

Sorbus arguta T.T. Yu, Acta Phytotax. Sin. 8(3): 223. 1963.

≡ Micromeles arguta (T. T. Yu) Mezhenskyj, NULESU Coll. Fruit Ornament. Pl.: 33. 2018.

≡ Wilsonaria arguta (T. T. Yu) Rushforth, Phytologia 100(4): 241. 2018.

= Aria yuarguta H. Ohashi et Iketani, J. Jap. Bot. 68(6): 361. 1993.

Type

China. Sichuan: Pingshan, Chingping Shan, 1120 m, 26 May 1934, T.H. Tu 5449 (holotype: PE[PE00934274]; isotype: PE[PE00934275])

Notes

When describing Sorbus arguta, Yü designated “T. H. Tu 5449” at PE (Fig. 2B) as the holotype (Yü and Kuan 1963). It was accepted by Yü and Lu (1974), Gabrielian (1978), Phipps et al. (1990) and Lu and Spongberg (2003). Ohashi and Iketani (1993) transferred it to genus Aria and proposed a new name A. yuarguta H. Ohashi et Iketan (Ohashi and Iketan 1993: 361) for A. arguta had been already used by Roemer in 1847 for a different species. Mezhenskyj transferred it to Micromeles (Mezhenska et al. 2018: 33) and Rushforth (2018: 241) transferred it to Wilsonaria.

However, Aldasoro et al. (2004) argued that: “S. arguta is a minor variant of S. megalocarpa and does not deserve taxonomic recognition”, and reduced it to a synonym of the later. A detailed study of the original material showed that Sorbus arguta is obviously different from S. megalocarpa. Sorbus arguta has oblong-ovate or ovate-lanceolate leaves with double serrate margins, relatively small corymbs (2–4 cm in diameter) with few flowers, and small sub-globose fruits (1–1.2 cm in diameter) with sparse lenticels, while S. megalocarpa has leaves with crenate-serrate margins, large corymbs (10–15 cm in diameter), many flowered (124–258 flowers per inflorescence), and much larger fruits with dense lenticels. Furthermore, S. arguta flowers after leaves are unfolded in early May (Fig. 3A, CBDI0226241), whereas S. megalocarpa flowers simultaneously with or before the leaves are unfolded in March (Fig. 3B, C). Therefore, S. arguta is treated as a distinct species here following Yü and Lu (1974), Gabrielian (1978), Phipps et al. (1990) and Lu and Spongberg (2003).

Figure 3. 

Corymbs of Sorbus arguta and S. megalocarpa A flowering specimen of Sorbus arguta (CBDI0226241) collected by Liang Zhang, Xinmao Zhou and Wenbin Ju, 7 May 2014 B Sorbus megalocarpa at blossoming stage, 21 March 2021 C detail of the inflorescence of S. megalocarpa (B, C were taken by Tailun Hu).

Representative specimens examined. China. Sichaun: Xinwen county, Xianfeng town, Monkey Bay, 1290 m, 12 May 1959, Yibin wild economic plants collection team 0368 (CDBI); Xuyong county, Heishuihe Nature Reserve, 1500 m, 6 June 2007, D.H. Zhu, Z.B. Feng, C. Zhang, F. Wang 20070776 (WCSBG); Xuyong county, Shuiwei town, Xixi village, 28°09'00"N, 105°20'40"E, 1100 m, 7 May 2014, L. Zhang, X.M. Zhou, W.B. Ju HGX14304 (CDBI); Xuyong county, Shuiwei town, Xixi village, 28°08'01"N, 105°22'20"E, 1230 m, 29 July 2014, W.B. Ju HGX14833 (CDBI).

Acknowledgements

This work was supported by the Natural Science Foundation of Jiangsu Province (grant no. BK20141472) and the Priority Academic Program Development of Jiangsu Higher Education Institutions, Jiangsu Province, China (PAPD). Many thanks go to Prof. Yunfei Deng (IBSC), Prof. Libing Zhang (MO), the reviewers and the editor for the valuable comments and suggestions on the manuscript. We also thank Tailun Hu for the photos of Sorbus megalocarpa and appreciate the assistance of Yuming Qian, who prepared the figures.

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