Report on the chromosome numbers of four Carex taxa in Korea (Cyperaceae)
Article information
Abstract
We report the meiotic chromosome numbers of four Carex taxa from Korean populations. Three are the first reports made on taxa from Korean populations: Carex appendiculata (Trautv. & C. A. Mey.) Kük. (n = 27II), C. fernaldiana H. Lév. & Vaniot (n = 33II), and C. metallica H.Lév. (n=15II). Reports on the other species expand the range of variation in the chromosome number within a taxon, C. miyabei Franch. (n = 43II, 44II, 45II). Carex L. (Cyperaceae) consists of more than 2,000 species worldwide and is the most species-rich genus in Korea. The species diversity in the genus has been hypothesized to be associated with the chromosome variation, but chromosome information pertaining to Korean Carex taxa is not well known. This report updates the chromosome number inventory on Korean Carex to 24 out of 180 taxa.
Chromosome information has long been an interesting research topic to numerous natural scientists. Chromosome contains hereditary genomic information allowing us to understand functional, structural, genetic, and evolutionary features of organisms. Chromosome number information detects major genomic events such as aneuploidy and polyploidy and has been consistently investigated (Guerra, 2008; Rice et al., 2015). In plant systematics, cytotaxonomic, phylogenetic and speciation inferences of chromosome numbers have been appreciated throughout the vascular pant lineages (de Azkue and Martĩnez, 1990; Chung and Kim, 1997; McArthur and Sanderson, 1999; Windham and Yatskievych, 2003; Peruzzi et al., 2009; Rockinger et al., 2016).
In Carex L. diversity research, chromosomes have provided critical information in various levels of taxonomic and phylogenetic groups, dealing with taxonomic delimitation, gene flow, lineage divergence, and evolution rate related questions (Tanaka, 1948; Davies, 1956; Rothrock and Reznicek, 1996; Hoshino, 1981; Rothrock et al., 2009; Hipp et al., 2010; Chung et al., 2012; Escudero et al., 2012). The genus is the most species-rich group in the temperate zones with more than 2,000 species worldwide (Global Carex Group, 2015). As a holocentric chromosome group, chromosome number increase and/or decrease without DNA duplication and/or deletion events (agmatoploidy and symploidy) (Luceño and Guerra, 1996; Hipp et al., 2013) might cause relatively rapid speciation (Hipp et al., 2010; Chung et al., 2012; Escudero et al., 2012). Although chromosome information has been considered critical features for Carex diversity, chromosome numbers of about only 20 taxa out of 180 Korean taxa have been documented (Kim, 2006; Lee and Kim, 2008; Chung et al., 2013; Chung et al., 2016; Chung et al., 2017; Chung et al., 2018; Chung and Im, 2018).
In this study, we report meiotic chromosome numbers for four Carex species from Korean populations and discuss their taxonomic and cytological significances: C. miyabei Franch., C. metallica H. Lév., C. fernaldiana H. Lév. & Vaniot, and C. appendiculata (Trautv. & C. A. Mey.) Kük.
Materials and Methods
Spikes with unopened staminate flowers were fixed in March and/or April, and voucher specimens with fully mature perigynia were collected in May and/or June, either 2018 or 2019. The methods for chromosome observation were applied as described in Rothrock and Reznicek (1996) and Chung et al. (2016). Fixed anthers in a fixing mixture of methanol, chloroform, and propionic acid (6:3:2) were squashed in 1% acetic-orcein and then observed at 1,000× magnification (Nikon Eclipse 50i, Nikon, Tokyo, Japan). To have solid meiotic chromosome numbers, each figure observed was drawn and photographed. In addition, variations in meiotic chromosome numbers (n) were determined after observations of at least three pollen mother cells per sample. All voucher specimens were identified following Hoshino et al. (2011) and Park et al. (2016), and deposited at the Korea National Arboretum Herbarium (KH) (Table 1).
Carex taxa investigated with voucher specimens and chromosome numbers.
Results and Discussion
Observed meiotic chromosome numbers are presented with previous records in Table 1, and representative meiotic chromosome figures are given in Fig. 1. All chromosomes are very short, less than 1 μm long, and distinct primary constriction cannot be pointed, which is one of characteristics of holocentric chromosomes (Hipp et al., 2013; Cuacos et al., 2015). Furthermore, bivalents are only observed in all the meiotic chromosomes in the present study.
Photomicrographs of Carex meiotic chromosomes. A. C. miyabei (n = 43II, Chung 6077). B. C. metallica (n = 15II, Chung 5150). C. C. fernaldiana (n = 33II, Chung 6048-1). D. C. appendiculata (n = 27II, Chung 6070). Scale bars = 5 μm.
Carex miyabei (n = 43II, 44II, 45II) (Fig. 1A) – Sect. Carex
The meiotic chromosome numbers of the species vary, n = 43II, 44II, 45 II. The counts are incongruent with previous reports from Korean populations, 2n = 66, 72 (Chung and Im, 2018), 2n = 84 (Chung et al., 2018); and a Japanese population, 2n = 90 (Tanaka, 1948). The species has been considered as a Japanese endemic, but recently distributions of the species in Japan and Korea have been known (Im et al., 2008; Hoshino et al., 2011; Park et al., 2016). Although C. miyabei is distinctly characterized pubescent perigynia with long beaks, and pistillate scales with aristate apexes, the species has been often confused with C. glabrescens (Kük) Ohwi for similarity on female spike numbers (more than two), and sharing ecological habitats (Im et al., 2008). These species occur throughout South Korea, but the latter grows mainly middle parts of South Korea (Park et al., 2016). Because both favor sunny, sandy places along rivers, it is not hard to find populations of the two taxa close each other (Im et al., 2008; Park et al., 2016). Variations in morphological characters such as perigynium shapes and surface features have made it hard to distinguish them from each other. Chromosome numbers of C. glabrescens have not been reported. As proposed in the previous studies (Chung and Im, 2018; Chung et al., 2018), taxonomic and cytological research should be conducted to understand the two morphologically challenging taxa in the section with taxon sampling covering the distribution areas of the taxa.
Carex metallica (n = 30II) (Fig. 1B) – Sect. Hymenochlaenae
The meiotic chromosomes of C. metallica from a Korean population is observed for the first time, n = 30II, which is identical to a previous report from Japan (Hoshino et al., 2011). The species only occurs in Jeju Island, South Korea and is mainly distributed in southern parts of China and Japan (Park et al., 2016; Chen and Zhang, 2018; Masaki, 2018). Dai et al. (2010) reported distributions of the species in Fujian (China) and Taiwan. The Hymenochlaenae comprised of about 60 species in Africa, Asia, and Central and North America, and Europe, and many Asian species exhibit narrow distribution patterns (Dai et al., 2010). Thirteen taxa out of fifteen Chinese species in the section are endemic to China, and C. hondoensis Ohwi occurs only in Japan (Dai et al., 2010; Hoshino et al., 2011).
Carex fernaldiana (n = 33II) (Fig. 1C) – Sect. Mitratae
Chromosome number of n = 33II for C. fernaldiana is identified, which is the first report on the taxon from a Korean population. In Japanese populations, the species exhibits a range of chromosome number variations, 2n = 66–74 (Tanaka, 1948; Hoshino et al., 2011). Although the species is distinguished from closely related taxa such as C. stenostachys Franch. et Sav. and C. polyschoena by long rhizomes and glabrous perigynia (Park et al., 2016; Nam, 2017), C. fernaldiana is considered as a synonym of C. pisformis Bott (Govaerts, 2019). Govaerts (2019) lists homotypic names of C. fernaldiana: C. sachalinensis var. fernaldiana (H. Lév. & Vaniot) T. Koyama, C. pisiformis var. fernaldiana (H. Lév. & Vaniot) T. Koyama, and C. sachalinensis subsp. fernaldiana (H. Lév. & Vaniot) T. Koyama. Nomenclatural synonyms need to be reevaluated. The evaluation should be conducted along with examinations on taxonomic synonyms covering the distribution areas of C. fernaldiana and C. pisiformis complex.
Carex appendiculata (n = 27II) (Fig. 1D) - Sect. Phacocystis
For the first time, chromosome number of C. appendiculata from a Korean population is revealed, n = 27II. Previously, 2n = 76 and c. 80 were reported from Russia (Krogulevich, 1976; Zhukova and Petrovsky, 1976). The species is mainly distributed in northern areas of South Korea and is characterized with 1–2 terminal female spikes and broad perigynia (Park et al., 2016). Although taxonomic status and delimitation are not congruent among distributed countries, the species occurs in China (north east), Japan (north), Russia (east), and Korea (north) (Dai et al., 2010; Hoshino et al., 2011, Ji, 2013; Park et al., 2016; Chen and Zhang, 2018; Masaki, 2018).
Counts on three taxa are the first reports from Korean populations: Carex appendiculata (Trautv. & C. A. Mey.) Kük. (n = 27II), C. fernaldiana H. Lév. & Vaniot (n = 33II), and C. metallica H.Lév. (n = 15II). The reports on the other species increase a range of variation in chromosome number within a taxon: C. miyabei Franch. (n = 43II, 44II, 45II). The counts confirm that chromosome number variations within and/or among taxa resulted from aneuploidy/agmatoploidy, and connote high species diversity in Carex. The report updates chromosome number inventory on Korean Carex to 24 taxa out of 180 taxa. Accumulating chromosome number data in Carex contributes to understanding species diversity of the genus.
Acknowledgements
We thank Dr. Takuji Hoshino and Tomomi Masaki (Okayama University of Science) for suggestions on chromosome experiments and observations.
Notes
Conflict of Interest
The authors declare that there are no conflicts of interests.