184 ACTA BOT. CROAT. 80 (2), 2021 Acta Bot. Croat. 80 (2), 184–190, 2021 CODEN: ABCRA 25 DOI: 10.37427/botcro-2021-021 ISSN 0365-0588 eISSN 1847-8476 One new species of Cymbella C.A. Agardh (Bacillariophyta) from high altitude lakes in the Hengduan Mountains of Southwest China Qi Liu1, Han Wu1, Yan-Ling Li1,*, John Patrick Kociolek2 1 Institute for Ecological Research and Pollution Control of Plateau Lakes, School of Ecology and Environmental Science, Yunnan University, Kunming 650500, P. R. China 2 Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado – 80309, USA Abstract – This paper describes a new species of the genus Cymbella C.A. Agardh from an alpine lake in the Heng- duan Mountains of southwestern China. A detailed morphological description of the new species, named Cymbella luoyulanae sp. nov., is presented; the description is based on light and scanning electron microscopy. The main fea- tures of C. luoyulanae are strongly dorsiventral valves with strongly reverse-lateral raphe branches near the proximal ends, a large central area occupying approximately a half of the width with the valve and slit-like areolae comprising striae that may be unseriate or partially biseriate. The new species has morphological characteristics that resemble those of C. heihainensis Y.Li et Gong, C. modicepunctata Krammer and C. asiatica Metzeltin, Lange-Bertalot et Y.Li, but it differs from these three species in details of size, valve shape, striae density, central area, and number of stigmata. Keywords: China, Cymbella, diatom, new species, taxonomy, SEM Introduction Diatoms from the Yunnan plateau have been only cur- sorily studied in the past (Skuja 1937, Zhu and Chen 1994, Li et al. 2007a,b). Cymbella C.A. Agardh (1830: 1) is one of the largest diatom genera, representing nearly two thousand described taxa (Kociolek et al. 2020a). However, in the past 30 years, the family Cymbellaceae has been split by some researchers more finely (Kociolek and Stoermer 1987, Krammer 1997a,b, Lange-Bertalot and Genkal 1999, Kram- mer 2002, 2003, Jüttner et al. 2010a, Bahls 2015, Kulikovskiy et al. 2014, 2015, Kulikovskiy and Kuznetsova 2016, Kapus- tin et al. 2017, 2020, Kociolek et al. 2017, Glushchenko et al. 2019, Kezlya et al. 2020). As a result of this recent work about 20 different genera are recognized (Tab. 1). Since the revision of Cymbella, a number of other new species have been described from China (summarized in Kociolek et al. 2020b, see also Li et al. 2019, Liu et al. 2020, Zhang et al. 2020). In southwestern China, specifically, Li et al. (2003a,b) described new species of Cymbella respective- ly from northwest Tibet and Qinghai Province. Gong and Li (2011) described a new species of Cymbella from the Yun- nan Plateau. Hu et al. (2013) described three new species of Cymbella from the high altitude lakes of the Hengduan Mountains region. In the present paper, we describe one new Cymbella species from the Hengduan Mountains area based on light and scanning electron microscopical inves- tigations and compare its morphology with similar species. Material and methods Samples were taken using a Kajak-type gravity core (Renberg and Hansson 2008) from the surface sediments of Lake Shadecuo (29°44′35.8′′ N, 101°21′39.8′′ E, Tab. 2), lo- cated in the eastern Hengduan Mountains region of South- west China. The pH and specific conductivity of the lake water were measured in the field using a YSI 650 multi-pa- rameter display system (650 MDS, YSI Incorporated 1700/1725 Brannum Lane, Yellow Springs, OH 45387 USA) with a 600 XL probe. Water samples were taken from 50 cm under the water surface. Transparency was estimated using a Secchi disk. Total nitrogen (TN) and total phosphorus * Corresponding author e-mail: yanlingli@ynu.edu.cn NEW SPECIES OF DIATOM FROM CHINA ACTA BOT. CROAT. 80 (2), 2021 185 (TP) were measured by a Shimadzu UV 2450 ultraviolet- visible spectrophotometer at Nanjing Institute of Geogra- phy and Limnology, Chinese Academy of Sciences, using the alkaline potassium persulfate digestion-UV spectro- photometric method (Nydahl 1978) and the ammonium molybdate spectrophotometry method (Ebina et al. 1983), respectively. Diatom samples were kept under 4 °C in the refrigerator before laboratory treatments. In the laboratory, the diatoms were treated with HCl and H2O2 (Battarbee 1986). Perma- nent slides were made from cleaned materials and mounted in Naphrax® for observation with light microscopy (LM; Olympus, BX-51, DIC). Relative abundances of diatoms in the samples were determined with a count of 300 valves. Cleaned materials were investigated with a Leo 1530 scanning electron microscope (SEM). Samples and slides are preserved in the Herbarium of Nanjing Institute of Geogra- phy and Limnology, Chinese Academy of Sciences, China. Results Taxonomy Class Bacillariophyceae Haeckel 1878 Subclass Bacillariophycidae D.G. Mann in Round et al. 1990 Order Cymbellales D.G. Mann in Round et al. 1990 Family Cymbellaceae Greville 1833 Genus Cymbella C.A.Agardh 1830 Cymbella luoyulanae Y.Li sp. nov. Fig. 1 A-E; Fig. 1C is the holotype LM (Fig. 1): Valves moderately dorsiventral. Dorsal margin strongly convex. Ventral margin concave, slightly tumid in middle. Valve ends slightly truncated and broadly rounded. Length 59-82 μm, width 16.0-18.5 μm, maximum length/ width ratio ca. 4.5. Axial area moderately broad. Central area elliptical, about 1/4-1/3 of width of valve. Raphe dis- tinctly lateral, abruptly reverse-lateral near proximal ends. Striae slightly radiate, becoming more radiate towards valve ends. 3-5 stigmata, some larger than others, occur ventral- ly from central nodule, distant from middle ventral striae. Striae 7-8/10 μm at centre becoming 10-12/10 μm towards apices, with 20-22 areolae in 10 μm. In SEM external valve view (Fig. 2): Striae uniseriate, part- ly biseriate with elliptical and transapically oriented areolae. Areolae slit-like with apically-orientated openings in trans- apical striae (Fig. 2 A-F). Stigmata rounded, separated from the areolae at central area on ventral side. Small round de- pressions may occur on the dorsal side of the central area (Fig. 2 C, D). Raphe centrally located on the valve face in a Tab. 1. A chronological listing of genera based on species formerly in the genus Cymbella or closely related genera (Zhang et al. 2021). * indicates the genus may be more closely related to freshwater gomphonemoid diatoms. Genera References Encyonema Kützing (1833: 589) Kützing 1833 *Reimeria Kociolek et Stoermer (1987: 457) Kociolek and Stoermer 1987 Pseudencyonema Krammer (1997: 156) Krammer 1997a Encyonopsis Krammer (1997: 156) Krammer 1997b Cymbellopsis Krammer (1997: 157) Krammer 1997b Cymbopleura Krammer (1999: 292) Krammer 2003 Navicymbula Krammer (2003: 123) Krammer 2003 Delicata Krammer (2003: 110; recently renamed as Delicatophycus M.J. Wynne 2019: 1) Krammer 2003 Gomphocymbellopsis Krammer (2003: 127) Krammer 2003 *Afrocymbella Krammer (2003: 129) Krammer 2003 Krsticiella Levkov in Levkov et al. (2007: 14–15) Levkov et al. 2007 Oricymba Jüttner et al. (2010: 408) Jüttner et al. 2010a Ochigma Kulikovskiy, Lange-Bertalot et Metzeltin (2012: 214) Kulikovskiy et al. 2012 Khursevichia Kulikovskiy, Lange-Bertalot et Metzeltin (2012: 157) Kulikovskiy et al. 2012 Kurtkrammeria Bahls (2015: 6) Bahls 2015 Celebesia Kapustin, Kulikovskiy et Kociolek (2017: 153) Kapustin et al. 2017 Karthickia Kociolek, Glushchenko et Kulikovskiy (2019:606) Glushchenko et al. 2019 Tab. 2. Physical and chemical parameters in Lake Shadecuo. Lake Shadecuo Latitude (°N) 29°44′35.8′′ Longitude (°E) 101°21′39.8′′ Altitude (m a.s.l.) 4428 Maximum depth (m) 8 pH 7.66 Secchi disk depth (m) 4.8 Total nitrogen (mg·L–1) 0.288 Total phosphorus (mg·L–1) 0.004 Conductivity (μs·m–1) 33 LIU Q., WU H., LI Y.-L., KOCIOLEK J. P. 186 ACTA BOT. CROAT. 80 (2), 2021 narrow hyaline axial area with straight to slightly dorsally arched proximal ends (Fig. 2 A, B). External distal raphe ends deflected dorsally (Fig. 2 E, F); external proximal raphe ends dilated (Fig. 2 C, D). The apical pore fields present and comprised by a group of porelli, almost entirely on the valve mantle (Fig. 2 E, F). In SEM internal valve view (Fig. 3): Striae with internal areolae openings lack any occlusions (Fig. 3 A, B). The cen- tral area distinct, projecting internally, and lacking an in- termissio. Stigma opening round, with a slight expanded depression evident on the central nodule. Stigmata lack any ingrowths or occlusion (Fig. 3 C, D). Distal raphe endings bent slightly towards the dorsal margin, terminating in he- lictoglossae. (Fig. 3 E, F). Type: – CHINA. Sichuan Province: Kangding City, Lake Shadecuo, 29°44′35.8′′ N, 101°21′39.8′′ E, elevation 4428 m a.s.l., samples collected by Dr. Yulan, Luo, 14th October 2017. Holotype Shadecuo 1-1 in Coll. Li Yanling, Yunnan Univer- sity., Kunming, China. Fig. 1 is of the holotype. Etymology: –The specific epithet ‘luoyulanae’ refers to the collector of the sample on which these observations are based. Fig. 1. Light microscopy micrographs of the type population of Cymbella luoyulanae sp. nov. in Lake Shadecuo, China. A-E – valve views, showing the valve variability of the holotype popula- tion. Fig. 2. External valve view of Cymbella luoyulanae sp. nov. by scanning electron microscope. A, B – external view of an entire valve. C, D – external view of valve center, the proximal raphe endings and the very large central area with 4-5 stigmata. E, F – valve apices, striae with slit-like areolae, some of them biseriate, and pore field separated by the distal raphe fissures. NEW SPECIES OF DIATOM FROM CHINA ACTA BOT. CROAT. 80 (2), 2021 187 Ecology Cymbella luoyulanae has been observed in the surface sediment sample from Lake Shadecuo. In Lake Shadecuo, this species was associated with Cyclotella ocellata Pantocsek (1902: 134) (20%), Achnanthidium minutissimum ( Kützing) Czarnecki (Czarnecki 1994: 157) (15%), C. comensis Grunow in Van Heurck (1882, pl. 93, Fig. 3 E, F) (14%), Pseudostaurosira pseudoconstruens (Marciniak) Williames et Round (1987: 275) (15%), and Staurosirella pinnata ( Ehrenberg) D.M. Williames et Round (1987: 274) (5%). Discussion The features found in Cymbella luoyulanae are com- pared to all other known species of the genus in Tab. 3. The taxon most similar to C. luoyulanae is C. heihainensis. The valves of this species are wider, have a larger central area, drop-like proximal raphe ends, and a higher number of ar- eolae in 10 µm, distinguishing it from C. luoyulanae. Cymbella modicepunctata has larger valves with a more dis- tinct central area, and fewer striae in 10 µm, distinguishing it from C. luoyulanae. Cymbella luoyulanae has stigmata that may vary in size along the ventral margin, while C. modicepunctata has uniformly-sized stigmata on the ventral side. The same stigmata feature of C. luoyulanae is also found in C. schimanskii Krammer and its variety var. excelsa ( Meister) Krammer. In SEM view, C. schimanskii has Y-shaped are- olae openings in the middle of the valve, which is different from the biseriate of C. luoyulanae, and they differ from C. luoyulanae by having larger valves, a smaller central area, Fig. 3. Internal valve views of Cymbella luoyulanae sp. nov. by scanning electron microscope. A, B – internal view of entire valve. C, D – showing the valve centre and four big and one small stigmata as elongated furrows connected to the striae. E, F – internal view of valve apex with prominent helictoglossa deflecting to the dorsal side. LIU Q., WU H., LI Y.-L., KOCIOLEK J. P. 188 ACTA BOT. CROAT. 80 (2), 2021 and in the shape of the central pores (rounded vs expanded as in C. luoyulanae). Cymbella luoyulanae can be distin- guished from C. asiatica by valve size and striae density. Cymbella asiatica varies between 50 and 105 µm in length and 14-18 µm in breadth, has no stigmata-like depressions on the dorsal side, and only 6-7 striae in 10 µm. Cymbella luoyulanae is also similar to C. arctissima Metzeltin, which can be distinguished from our new species which has dor- sally deflected proximal raphe endings, is shorter (98-105 µm vs. 59-94 µm), and has a broader central area (2/3 width vs. 1/2 width). Another member of the genus Cymbella, C. distalebise- riata Bing Liu et D.M. Williams in Liu et al. (2018: 41), was described from Hunan Province, China. Cymbella distalbi- seriata shares the feature of having striae with uniseriate and partially biseriate striae. The only other species of Cym- bella exhibiting (a few) biseriate striae include C. yakii Jüt- tner et Van de Vijver in Jüttner et al. (2010b), C. duplopunc- tata Krammer 2002 and C. buechleri Krammer 2002 (both described from a fossil deposit in western North America). Three of the five species exhibiting biseriate striae are found in Asia, and two have been described from China. The oth- er two taxa with biseriate striae are known from a fossil de- posit in western North America (apparently of Miocene age, see Krammer 2002, p. 109). These are distinct from one an- other in size, shape and other morphological features (Krammer 2002, Jüttner et al. 2010b, Liu et al. 2018). It is unclear if the possession of biseriate striae is a homologous feature for this group or not; formal phylogenetic analysis is required to understand character evolution in this regard. However, if the taxa with biseriate striae are indeed closely related among themselves and their distribution remains between Asia and western North America, it supports the notion, noted by Ehrenberg over 180 years ago (Ehrenberg 1849) and supported by additional diatom examples (Koci- olek and Stoermer 1989, Kociolek et al. 2013, 2015, Genkal and Kulikovskiy 2016, Kociolek 2019) as well as some genera of higher plants (Xiang and Soltis 2001, Nie et al. 2006, Ka- dereit and Baldwin 2012), of there being a close relationship between the floras of these two areas. Acknowledgments This work was supported by the projects of the Nation- al Sciences and Foundation of China (Grant No. 41877296, 41877434, and 42077424). References Agardh, C.A., 1830: Conspectus criticus diatomacearum. Part 1. Litteris Berlingianis, Lund. Bahls, L.L., 2015: Kurtkrammeria, a new genus of freshwater di- atoms (Bacillariophyta, Cymbellaceae) separated from En- cyonopsis. Nova Hedwigia 101, 165–190. 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