Carex L. is one of the most species diverse genera in flowering plants with more than 2,000 species worldwide (Global Carex Group, 2015). Along the great species diversity, the genus has high intraspecific variation in chromosome numbers due to holocentric chromosomes, which have diffused or nonlocalized centromeres (Hipp et al., 2009; Escudero et al., 2012). Within the genus, chromosome numbers dramatically vary, from n = 6 to n = 66; and taxa with high variations in chromosome numbers within species and/or individuals have been detected in recently diverging lineages (Tanaka, 1949; Roalson, 2008; Hipp et al., 2009). The chromosome features can have chromosome number increases (fission, agmatoploidy) and/or decreases (fusion, symploidy) without DNA duplication/deletion events (Hipp et al., 2013). Genome size and chromosome number in Carex have been hypothesized to be decoupled evolutionary features (Chung et al., 2012). The cytological features are critical to understand species richness of Carex (Hipp et al., 2009; Global Carex Group, 2015).
In the flora of Korea, Carex is the largest genus with about 157 taxa in Cyperaceae, the second largest family with 246 species in 13 genera (Oh, 2007). Although chromosome information is critical to understand diversity in Carex, most species have not been investigated using cytological tools. Among Korean native taxa, only 24 Carex taxa have been reported with chromosome numbers, and the genome sizes of 43 Carex taxa have been estimated (Chung and Im, 2019; Lee et al., 2019). The cytological information is too little to understand Carex diversity in the flora.
In the present study, we report meiotic chromosome numbers of eight Carex taxa observed from Korean populations: C. accrescens Ohwi, C. lanceolata Boott, C. bostrychostigma Maxim., C. breviculmis R. Br., C. polyschoena H.Lév. & Vaniot, C. sabynensis Less. ex Kunth, C. planiculmis Kom., and C. paxii Kük.
Materials and Methods
Immature male spikes were used for meiotic chromosome number observation. Entire spikes were preserved in a fixative containing methanol, chloroform, and propionic acid (6:3:2) and then transferred to 70% ethanol (Rothrock and Reznicek, 1996; Chung et al., 2016). Fixed anthers were squashed in 1% acetic-orcein and observed at 1,000× magnification (Nikon Eclipse 50i, Nikon, Tokyo, Japan). To determine chromosome numbers and variation ranges, more than two meiotic division cells per individual were observed, analyzed, and photographed. Taxon identification followed Park et al. (2016) and Hoshino et al. (2011), and infrageneric classification was adopted from Global Carex Group (2020). Voucher specimens with mature perigynia were stored at Andong National University herbarium (ANH).
Results and Discussion
Meiotic chromosome numbers of eight Carex taxa were summarized in Table 1. Sections and species were organized in alphabetical order. All the species exhibited consistent chromosome numbers within individuals and had the normal bivalents paring in meiotic division. Among the four species observed more than one population, C. bostrychostigma and C. sabynensis did not exhibit variation in chromosome number. However, two C. planiculmis individuals had variation with n = 29II and 30II, and C. breviculmis varied in the meiotic chromosome numbers with 33II, 34II, and 36II. Their chromosomes were about 2 μm long, and constricted centromeres were not visible (Fig. 1).
Carex accrescens Ohwi 경성사초 (n = 37II) (Fig. 1A) – Sect. Ammoglochin Dumortier
Meiotic chromosome number of n = 37II was observed in C. accrescens (= C. pallida C. A. Mey.), which was the first count for the species. The species is characterized with long rhizomes, two types of spikes (male and androgynous) and ovoid perigynia with serrulate margins (Park et al., 2016; Hoshino et al., 2011). It occurs in East Asia, and most populations in Korea are found in wet and sandy habitats (Hoshino et al., 2011; Park et al., 2016; Japanese Society of Cyperology, 2018). Global Carex Group (2020) places the species in Disticha clade with total 27 taxa, which are treated in various traditional sections, Ammoglochin, Divisae, Holarrhenae, Foetidae, Phaestoglochin, and Phleoideae.
Carex lanceolata Boott 그늘사초 (n = 36II) (Fig. 1B) – Sect. Clandestinae G. Don
For the first time, chromosome number of C. lanceolata from a Korean population was counted, n = 36II. Previous counts from Japanese populations are two numbers, 2n = 70 and 2n = 72 (Hoshino, 1981; Hoshino and Ikeda, 2003). In both South Korea and Japan, the species commonly grows (Park et al., 2016; Japanese Society of Cyperology, 2018). The species is classified in sect. Clandestinae by traditional and phylogenetic criteria (Global Carex Group, 2020).
Carex bostrychostigma Maxim. 길뚝사초 (n = 22II) (Fig. 1C, D) – Sect. Debiles (J. Carey) Ohwi
From two individuals of C. bostrychostigma, chromosome numbers of n = 22II were observed, which were first counts from Korean populations and different from the previous report from a Japanese population (2n = 46 in Hoshino et al., 2011). In South Korea, the species is very common occurring throughout the country, whereas it is found only in Honshu and Kyushu in Japan (Park et al., 2016; Japanese Society of Cyperology, 2018). More investigations targeting broad distribution areas should be conducted to determine chromosome number variation range in the species. Global Carex Group (2020) places the species in Dissitiflora clade with C. dissitiflora Franch., which is endemic to Japan and traditionally in sect. Mundae (2n = 36, 38) (Hoshino et al., 2011).
Carex breviculmis R.Br. 청사초 (n = 33II, 34II, 36II) (Fig. 1E–H) – Sect. Mitratae Kükenthal
Three different chromosome numbers were observed from four populations. Chromosome numbers of n = 33II and n = 34II are previously reported from Korean populations (Chung et al., 2017, 2018; Chung and Im, 2020), but n = 36 II is the first count from a Korean population, which is previously reported from Japanese populations (Okuno, 1939). The species relatively common in Korea and Japan, occurring in Asia such as Taiwan, Russia, and Himalaya (Park et al., 2016; Japanese Society of Cyperology, 2018). Traditionally the species is classified in sect. Mitratae Kük., and recent classification shows that the species forms a clade named Mitrata with majority of Mitratae members (Global Carex Group, 2020). High chromosome variation in the species, from 2n = 54 to 2n = 72 (not continuous), might be related with broad distribution or with confuse of taxonomic complex such as species delimitation.
Carex polyschoena H.Lév. & Vaniot 가지청사초 (n = 37II) (Fig. 1I) – Sect. Mitratae Kükenthal
Chromosome number of n = 37II was observed for C. polyschoena. The species is only found in Korea and Japan. In South Korea, the species is very common occurring throughout the country, whereas the species occurs only in Tsushima, Kyushu, Japan (Hoshino et al., 2011; Park et al., 2016). Various chromosome numbers for the species have been reported from Korean populations (2n = 52, 72, 74, 76) (Chung et al., 2016, 2018; Chung and Im, 2020). The species is classified in Conica clade with 48 species, which are mainly Mitratae members distributed in Asia (Global Carex Group, 2020).
Carex sabynensis Less. ex Kunth 실청사초 (n = 28II) (Fig. 1J, K) – Sect. Mitratae Kükenthal
Chromosome number of n = 28II was observed from two individuals of C. sabynensis, which was identical to the previous report from a Korean population in Chung et al. (2016). Five different chromosome numbers have been reported for the species (2n = 40, 54, 56, 60, 76) (Table 1). The species occurs throughout the country in South Korea, whereas it grows in Hokkaido, Honshu, and Kyushu in Japan (Hoshino et al., 2011; Park et al., 2016). It is also found in China and Russia (Park et al., 2016). Global Carex Group (2020) classifies the species in Conica clade, where C. polyschoena belonging to.
Carex planiculmis Kom. 그늘흰사초 (n = 29II, 30II) (Fig. 1L, M) – Sect. Molliculae Ohwi
Two chromosome numbers for C. planiculmis were observed, n = 29II and n = 30II. The chromosome number of n = 29II is a new count for the species. Chromosome number of the species ranges from 2n = 58 to 2n = 62, including observations made from Japanese and Korean populations (2n = 62, Tanaka, 1939; 2n = 60, Chung and Im, 2018). The species occurs in East Asia including north part of Japan (Honshu and Hokkaido) and most provinces in Korea (Park et al., 2016; Japanese Society of Cyperology, 2018). Traditionally, the species is classified in sect. Molliculae and the section is well supported in phylogenetic research. However, C. planiculmis position in the section is not supported by phylogenetic data and remains unresolved (Global Carex Group, 2020).
Carex paxii Kük. 대구사초 (n = 38II) (Fig. 1N, O) – Sect. Phleoideae Meinshausen
For the first time, a chromosome number of C. paxii from a Korean population was counted, which was identical to the previous count made from Japanese populations (Hoshino, 1981, 1986). In both Japan and Korea, only a few natural populations have been reported, and the species also occurs in China (Park et al., 2016; Japanese Society of Cyperology, 2018). The species has been classified in sect. Phleoideae in traditional classification, but the phylogenetic data have moved it to Disticha clade composed of some numbers of six traditional sections (two Ammoglochin, one Divisaae, ten Holarrhenae, nine Foetidae, four Phaestoglochin, and one Phleoideae taxa) (Global Carex Group, 2020). Among nine taxa in the traditional section Phleoideae, C. paxii is the only species not supported by the sectional classification but is grouped with North American and Eurasian species in Disticha clade (Global Carex Group, 2020).
Most Carex species are assigned in revised phylogenetic classification, but many clades miss morphological and/or geographic synapomorphies (Global Carex Group, 2020). It is unlikely that a single character would explain lineage divergences, but combinations of characters might be able to interpret current lineages. Chromosome variation within species is common in the genus, and genetic diversity explains lineage diversity and limitations in some lineages with enough cytological data available (Hipp et al., 2009; Chung et al., 2012). It is challenging to obtain cytological information due to living material availability and maintenance. However, further work on cytological data is critical to understand infrageneric lineage and species diversity in the genus.
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