INTRODUCTION
Carex L. is the most species-rich genus in the temperature zones with more than 2,000 species worldwide and the most diverse genus in the Korean flora with about 180 taxa in 42 sections (Global Carex Group, 2015; Park et al., 2016). The high species diversity in the genus has been postulated to be related to rapid chromosome speciation of holocentric chromosomes (Hipp et al., 2007, 2009). Holocentric chromosomes miss localized single centromeres during cell divisions and can fuse and/or fission resulting in decreases and/or increases of chromosome numbers (Hipp et al., 2013). The unusual acentric chromosomes have been found in several lineages in flowering plants such as Drosera (Droseraceae) and Luzula (Juncaceae) (Kuta et al., 2004; Kolodin et al., 2018). Among holocentric chromosome-possessing groups, only Carex has exhibited high species diversity (Roalson et al., 2007; Roalson, 2008).
To understand Carex diversity in the Korean flora, chromosome information of each taxon is critical. Out of 180 Korean Carex taxa, 37 taxa (20 sections) have been reported with chromosome numbers, which exhibit variation from 2n = 12 to 2n = 108 (Nam et al., 2025). Among flowering plants, the variation in chromosome numbers is exceptionally diverse at a generic level. Consistent efforts to document chromosome information in Carex have been made.
In this paper, the chromosome numbers of six taxa are reported, including the first reports for two taxa: C. erythrobasis, C. tegulata, C. breviculmis, C. brevispicula, C. polyschoena, and C. sabynensis. Significance of each chromosome number is discussed in traditional as well as recently revised Carex classifications.
MATERIALS AND METHODS
To observe meiotic chromosomes, male spikes were fixed during early spring from 2022 to 2025 following the methods for Carex in Chung and Chung (2021). A mixture of methanol, chloroform, and propionic acid mixture was used for fixation. To confirm chromosome numbers and variation ranges within individual and/or species, at least three cells per sample were analyzed: Chung 10099 and 10141 (five cells), Chung 10128 and 10129 (three cells), Chung 10087 (four cells), Chung 9031 (seven cells), and Chung 10146 (six cells). Voucher specimens with mature fruits (perigynia) were collected in 2025 and identified following Hoshino et al. (2011), Park et al. (2016), and Nam et al. (2020). They were deposited in the herbarium of the Korea National Institute of Biological Resources (KB).
RESULTS AND DISCUSSION
Meiotic chromosomes of six Carex species in three sections were analyzed (Table 1). All chromosomes did not exhibit constricted centromeres and were very small, less than 2 μm in length (Fig. 1). Furthermore, only bivalent chromosomes were observed.
Carex erythrobasis H. Lév. & Vaniot 한라사초 (n = 13II) (Fig. 1A, B) – Sect. Clandestinae G. Don.
For the first time, the chromosome number of n = 13II for C. erythrobasis was observed. Compared to the previous reports from the section in Korea, n = 36 II (C. pediforms var. pedunculata and C. lanceolata), C. erythrobasis has a low chromosome number (Chung and Chung, 2021; Lee and Chung, 2023). The section Cladestinae is characterized by short distal leaves (about 1 cm long), colored (brownish or dark-purplish brown) female scales, and pubescent perigynia (mostly) and is composed with 20–35 species and five taxa are recognized in Korea (Crins, 2002; Park et al., 2016). In the recently revised classification, the section is divided into several groups (Concinna Clade, sect. Clandestinae, sect. Digitatae, Conica Clade, Incertae Sedis), and sect. Clandestinae clade includes almost half of the species traditionally classified in the section and sects. Aulocystis, Debiles, Decorae, and Mundae (Global Carex Group, 2021).
The species is characterized by purple-red or dark purple sheaths at base and loose female (lateral) spikes, and elliptic perigynia; and habits at semi-shady areas in China (S Jilin), Russia (Far East), and Korea (Dai et al., 2010; Park et al., 2016). It has been recognized as an endemic species in Korea (Park et al., 2016; Chung et al., 2017a). However, in a recently revised endemic taxon list, the species has been excluded (Chung et al., 2023a). In the most recently proposed classification, the species is placed in sect. Pictae with two Eastern and one Northern North American species (Global Carex Group, 2021). Among them, Carex pedunculata Muhl. Ex Willd. was reported with chromosome number (2n = 26) (Roalson, 2008). The Korean Clandestinae taxa reported with chromosome numbers, C. pediforms var. pedunculata and C. lanceolata, are stayed in the section in the revised classification (Global Carex Group, 2021).
Carex tegulata H. Lév. & Vaniot 구슬사초 (n = 27II) (Fig. 1C) – Sect. Phacocystis Dumort.
The meiotic chromosome number of n = 27II for C. tegulata was counted for the first time. Seven species in the sect. Phacocystis occurs in Korea, and one species, C. appendiculata has been reported with the same meiotic chromosome number, n = 27II (Park et al., 2016; Chung and Im, 2019). The species occurs near streams or rivers in Korea and Russia (Sakhalin) and is characterized by swollen perigynia (Park et al., 2016). In the most recently proposed classification, C. tegulata is treated in section Stylosae with the taxa traditionally classified in sects. Phacocystis (three species), Stylosae (three species), and Anomalae (one species) (Global Carex Group, 2021). Among eight taxa in the revised section Stylosae, C. aperta Boott (n = 27), C. haydenii Dewey (n = 27), C. meyeriana Kunth (n = 31), C. jaluensis Kom. (n = 27, 28, 29, 30), and C. stylosa C. A. Mey. (2n = 52) were reported with chromosome information, ranged from 2n = 52 to 2n = 62 (Roalson, 2008; Chung and Im, 2018).
Carex breviculmis R. Br. 청사초 (n = 33II) (Fig. 1D, E) – Sect. Mitratae Kük.
Additional chromosome investigations for C. breviculmis, one of the most common Carex species in South Korea, were conducted and found the meiotic chromosome number of n = 33II in two individuals (Table 1). The same meiotic chromosomes were observed in Korean populations (Chung et al., 2017b, 2018; Chung and Im, 2020; Chung and Chung, 2021; Masaki et al., 2024). The species distributes broadly and commonly in East Asia and exhibits broad variation in chromosome numbers, from n = 27 to n = 37 (Table 1) (Dai et al., 2010; Hoshino et al., 2011). Unlike most Carex species, C. breviculmis occurs in diverse ecological habitats including mountains, grassland, and even somewhat disturbed areas (Hoshino et al., 2011; Park et al., 2016). Although the species has been divided into several infraspecific taxa, detailed morphological and cytological investigations have not been conducted.
Carex brevispicula G. H. Nam & G. Y. Chung 좀목포사초 (n = 33II) (Fig. 1F, G) – Sect. Mitratae.
A new chromosome number for C. brevispicula was observed, n = 33II (Table 1). The species is endemic to Korea and has been reported with the consistent chromosome number of n = 34II (Nam et al., 2020; Chung et al., 2023b; Masaki et al., 2024). The species is characterized by pale green pistillate scales, smooth perigynia, and short lateral spikes (less than 15 mm); and occurs throughout South Korea on mountain and rocky slopes (Nam et al., 2020).
Carex polyschoena H. Lév. & Vaniot 가지청사초 (n = 38II) (Fig. 1H) – Sect. Mitratae.
The meiotic chromosome number for C. polyschoena was observed as n = 38II, which was reported before from a Korean population (Table 1) (Chung and Im, 2020). Various chromosome numbers have been reported for the species 2n = 52, 68, 72, 74, 76 (Chung et al., 2016, 2018; Chung and Im, 2020; Chung and Chung, 2021; Masaki et al., 2024). Although the species occurs in China, Japan, and Korea, only Korean populations have been investigated. It is one of common Carex species in Korea, occurring throughout the peninsula, and exhibits a great diversity in morphology such as inflorescence sizes and perigynium shapes (Park et al., 2016). In Japan and China, the species occurs in geographically restricted areas (Dai et al., 2010; Hoshino et al., 2011).
Carex sabynensis Less. ex Kunth 실청사초 (n = 27II) (Fig. 1I) – Sect. Mitratae.
the meiotic chromosome number of n = 27II was observed for C. sabynensis (Table 1). The chromosome number was found previously in three Korean populations (Chung et al., 2016, 2018; Chung and Im, 2020). The species occurs in China, Japan, Korea, and Russia (East) in open meadows or wet places in mountains (Hoshino et al., 2011; Park et al., 2016). Previously, various chromosome numbers were observed from Russian and Korean populations 2n = 40, 54, 56, 60, 76 (Krogulevich, 1971; Yurtsev and Zhukova, 1982; Chung et al., 2016, 2017b, 2018; Chung and Im, 2020; Chung and Chung, 2021).
In the recently revised infrageneric classification, the three Mitratae species are placed in two clades: C. polyschoena and C. sabynensis in a Conica Clade (total 48 species) and C. breviculmis in a Mitrata Clade (total 28 species) (Global Carex Group, 2021). Although C. brevispicula is not included in the classification, based on morphological characters, the species should be classified in a Mitrata Clade (Nam et al., 2020). Section Mitratae i s large with m ore than 8 0 taxa i n the traditional classification and diverse in morphology and cytology (Dai et al., 2010; Hoshino et al., 2011; Masaki et al., 2024). In the revised classification, taxa in the section are divided into several infrageneric groups: sect. Acrocystis (1 species), sect. Rhomboidales (1), Conica Clade (45), Mitrata Clade (28), Tristachya Clade (6), Truncatigluma Clade (1), and Incertae Sedis (5) (Global Carex Group, 2021).
Global Carex Group (2021) revised a Carex infrageneric classification, six subgenera with 62 formal sections and 49 informal groups, which is an intermediate step utilizing current phylogenetic information available because most traditional subgenera and sections were polyphyletic. The classification is required to be assessed, refined, and confirmed by morphological, geographical, and cytological information. Accumulated cytological data should be helpful to understand species and chromosomal diversity in such a taxonomically and phylogenetically challenging group.
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