Karyotype Report
Chromosome number report of six Carex sect. Mitratae taxa from the Korean Peninsula (Cyperaceae)
2024 Volume 89 Issue 3 Pages 251-255
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2024 Volume 89 Issue 3 Pages 251-255
Carex is the most species-rich group in the flowering plants in the temperate zones with more than 2,000 species worldwide. Coupled with the high species diversity, the genus possesses holocentric chromosomes, which miss constricted centromeres during cell divisions. Holocentric chromosomes are supposed to contribute to great variation in chromosome numbers by chromosome fragmentation (fission) and/or merging (fusion). Carex section Mitratae Kük. occurs mainly in East Asia and comprises about 80 taxa. Meiotic chromosome numbers of six taxa in the section were observed from 15 populations in South Korea: C. breviculmis R. Br. (n=32II, 33II, 34II), C. brevispicula G. H. Nam & G. Y. Chung (n=34II), C. candolleana H. Lév. & Vaniot (n=35II), C. conica Boott (n=18II, 19II), C. fibrillosa Franch. & Sav. (n=34II), and C. polyschoena H. Lév. & Vaniot (n=34II, 36II). All the chromosomes observed were very small (about 1–2 µm long) with diffuse centromeres (without constricted centromeres). Chromosome numbers vary in C. breviculmis, C. conica, and C. polyschoena. C. breviculmis and C. polyschoena show variation within a species (among populations), and C. conica exhibits two different numbers within a population. C. brevispicula, a Korean endemic, has a consistent chromosome number with previous counts, and C. fibrillosa shows the same chromosome number as the count from a Japanese population. For the first time, the chromosome number for C. candolleana is counted. Further investigations of chromosomes in Carex will help to understand the species diversity of the most species-rich group in flowering plants.
Carex L. is one of the most species-rich groups in flowering plants with more than 2,000 species worldwide (Global Carex Group 2015). It habits various ecological conditions including sunny, shady, humid, dry, forests, seashores, and swaps although most species occur in wet habitats (Dai et al., 2010; Hoshino et al. 2011; Global Carex Group 2015; Park et al. 2016). The high diversity has been hypothesized by holocentric chromosomes, which miss constricted centromeres during cell division (Hipp et al. 2013). Recently diverging groups usually have small-sized and high-numbered chromosomes, and genetically diverse groups exhibit great ranges in chromosome numbers (Hipp et al. 2009; Yano et al. 2014).
Carex section Mitratae Kük. is composed of about 80 species and distributed in Central, East, and Southeast Asia, Australia, Europe, and Pacific islands (Dai et al. 2010; Hoshino et al. 2011). Hoshino et al. (2011) revealed that this section has 80 taxa in Japan, and this number was the largest number of taxa in surrounding areas: China (27 taxa, Dai et al. 2010), Korea (21 taxa, Park et al. 2016), Russia and adjacent regions (19 taxa, Egorova 1999), and Taiwan (8 taxa, Hayata 1921). In Korea, the section is the largest and is commonly found in forests and mountain slopes (Park et al. 2016).
In the section, a great range of chromosome number variation within a taxon is found. The following taxa exhibit chromosome variations within a species: C. breviculmis (2n=54, 58, 62, 64, 66, 68, 70, 72, 74; Okuno 1939, 1940; Tanaka 1939, 1948; Hoshino 1981; Ohkawa and Yokota 1998; de Lange and Murray 2002; Chung et al. 2016, 2017, 2018; Chung and Im 2020; Chung and Chung 2021), and C. conica (2n=32, 33, 34, 36, 37, 38, 42; Okuno 1940; Tanaka 1948; Hoshino and Okamoto 1979; Hoshino 1980, 1981; Hoshino and Waterway 1994). In the section, the chromosome numbers reported range from 2n=20 to 2n=94 (Hoshino et al. 2011; Chung and Im 2020). In Korea, six members in the section have been reported with chromosome numbers: C. breviculmis (2n=54, 58, 62, 64, 66, 68, 72), C. brevispicula (2n=68), C. fernaldiana (2n=66), C. polyschoena (2n=52, 72, 74, 76), C. sabynensis (2n=54, 56, 76), and C. tristachya (2n=42) (Chung et al. 2016, 2017, 2018; Chung and Im 2019, 2020; Chung and Chung 2021; Chung et al. 2023). Some have fixed chromosome numbers, but there are some species with great variation in chromosome numbers.
To clarify variation range in chromosome number of Carex sect. Mitratae in Korea, we investigated commonly distributed taxa in the section. An accurate understanding of the chromosome number of each taxon is essential for effective taxonomy and speciation. We report meiotic chromosome numbers of six members in Carex section Mitratae from Korean populations: C. breviculmis R. Br., C. brevispicula G. H. Nam & G. Y. Chung, C. candolleana H.Lév. & Vaniot, C. conica Boott, C. fibrillosa Franch. & Sav., and C. polyschoena H.Lév. & Vaniot.
To obtain immature staminate flowers, a field survey was conducted in South Korea from April 2022 to April 2023. Six Carex taxa from 15 populations were suitable for meiotic chromosome observations (Table 1). Immature staminate flowers were sampled and treated in a mixture of methanol, chloroform, and propionic acid (6 : 3 : 1 by volume) (Lee and Chung 2023). The samples fixed were stored in 70% ethanol, and pollen cells were stained in 1% acetic-orcein and then squashed. Meiotic chromosomes observed at ×1,000 magnification were photographed. To confirm chromosome number, at least three meiotic cells per sample were analyzed. A microscope (Nikon Eclipse 50i, Nikon, Tokyo) was used for observation, and taxonomic treatment followed Hoshino et al. (2011) and Park et al. (2016). Voucher specimens were stored in the Herbarium of Chonnam National University (CNU).
| Taxon | Locality and collection date | Collector (voucher number) | Chromosomes counted (n) | Previous reports (2n) |
|---|---|---|---|---|
| C. breviculmis R. Br. | Dongbu-ri, Goesan-eup, Goesan-gun, Chungbuk, South Korea (April 20, 2022) | Chung 9019 | 34II | 54, 58 (Chung et al. 2016 reported as C. leucochlora) 62, 64, 66 (Chung et al. 2018) 64, 68 (Tanaka 1939) c.64 (de Lange and Murray 2002) 64, 68, 70, 72, 74 (Tanaka 1948) 64, 66, 68 (Chung and Im 2020) 66 (Chung et al. 2017) 66, 68, 72 (Chung and Chung 2021) 68 (Hoshino 1981 reported as C. leucochlora) 68 (Ohkawa and Yokota 1998 reported as C. leucochlora) 70 (Okuno 1940 reported as C. leucochlora) 72 (Okuno 1939) |
| Yuseo-ri, Saengil-myeon, Wando-gun, Jeonnam, South Korea (April 21, 2022) | Chung 9076 | 32II | ||
| Gyo-dong, Gongju-si, Chungnam, South Korea (May 20, 2022) | Chung 9077 | 32II | ||
| Gyo-dong, Gongju-si, Chungnam, South Korea (May 20, 2022) | Chung 9078 | 33II | ||
| Bongpyeong-dong, Tongyeong-si, Gyeongnam, South Korea (March 2, 2023) | Chung 9542 | 34II | ||
| Dongbu-ri, Goesan-eup, Goesan-gun, Chungbuk, South Korea (April 7, 2023) | Chung 9565 | 33II | ||
| Dongbu-ri, Goesan-eup, Goesan-gun, Chungbuk, South Korea (April 7, 2023) | Chung 9566 | 33II | ||
| Seongam-dong, Danwongu, Ansan-si, Gyeonggi, South Korea (April 1, 2023) | Chung 9576 | 34II | ||
| C. brevispicula G. H. Nam & G. Y. Chung | Bongpyeong-dong, Tongyeong-si, Gyeongnam, South Korea (March 2, 2023) | Chung 9544 | 34II | 68 (Chung et al. 2023) |
| C. candolleana H.Lév. & Vaniot | Yuseo-ri, Saengil-myeon, Wando-gun, Jeonnam, South Korea (April 21, 2022) | Chung 9073 | 35II | None |
| C. conica Boott | Sillye-ri, Namwon-eup, Seogwipo-si, Jejuteukbyeoljachido, South Korea (April 30, 2022) | Chung 9005-2 | 18II | 32–34, 36–38 (Hoshino 1980) 32, 34, 36–38 (Hoshino 1981) 32, 36 (Hoshino and Okamoto 1979) 34, 42 (Okuno 1940) 32–34, 36–38 (Hoshino and Waterway 1994) |
| Sillye-ri, Namwon-eup, Seogwipo-si, Jejuteukbyeoljachido, South Korea (April 30, 2022) | Chung 9014 | 18II, 19II | ||
| C. fibrillosa Franch. & Sav. | Ihoildong, Jeju-si, Jejuteukbyeoljachido, South Korea (April 30, 2022) | Chung 9125 | 34II | 68 (Tanaka 1948) |
| C. polyschoena H.Lév. & Vaniot | Geumgwang-myeon, Anseong-si, Gyeonggi, South Korea (May 27, 2022) | Chung 9052 | 34II | 52 (Chung et al. 2016) 72, 74 (Chung et al. 2018) 74, 76 (Chung and Im 2020) 74 (Chung and Chung 2021) |
| Geumgwang-myeon, Anseong-si, Gyeonggi, South Korea (May 27, 2022) | Chung 9062 | 36II |
Chromosome numbers of six species in Carex sect. Mitratae collected from 15 populations in South Korea were observed (Table 1). All the meiotic chromosomes were very small (about 1–2 µm long) and constricted centromeres were not distinct (Figs. 1, 2). C. breviculmis and C. polyschoena had different chromosome numbers among populations, and C. conica showed two different chromosome numbers within a population.
(A) C. breviculmis (n=34II, Chung 9019), (B) C. breviculmis (n=32II, Chung 9076), (C) C. breviculmis (n=32II, Chung 9077), (D) C. breviculmis (n=33II, Chung 9078), (E) C. breviculmis (n=34II, Chung 9542), (F) C. breviculmis (n=33II, Chung 9565), (G) C. breviculmis (n=33II, Chung 9566), (H) C. breviculmis (n=34II, Chung 9576), (I) C. brevispicula (n=34II, Chung 9544). Scale bars=10 µm.
(A) C. candolleana (n=35II, Chung 9073), (B) C. conica (n=18II, Chung 9005-2), (C) C. conica (n=18II, Chung 9014), (D) C. conica (n=19II, Chung 9014), (E) C. fibrillosa (n=34II, Chung 9125), (F) C. polyschoena (n=34II, Chung 9052), (G) C. polyschoena (n=36II, Chung 9062). Scale bars=10 µm.
C. breviculmis is characterized by staminate and pistillate spikes gathered on the top of culms and distributed in Japan, China, Russia, Taiwan, Himalaya, and Korea (Park et al. 2016). The chromosome reports of this species showed various numbers 2n=54, 58, 62, 64, 66, 68, 70, 72, 74 (Okuno 1939, 1940; Tanaka 1939, 1948; Hoshino 1981; Ohkawa and Yokota 1998; de Lange and Murray 2002; Chung et al. 2016, 2017, 2018; Chung and Im 2020; Chung and Chung 2021). In Korean populations, chromosome numbers of 2n=64, 66, 68, 72 have been found in the species (Chung et al. 2017, 2018; Chung and Im 2020; Chung and Chung 2021). Tanaka (1948) found 1–2 chromosome fragments (ca. 51.0%) in the first meiotic metaphase of 2n=70 and pointed out that 2n=72 of primary pollen nuclear division variations (n=35, 36, 37), which was referred from unusual pairs in the first meiotic metaphase. At meiotic metaphase I of three aneuploids, n=32II, 33II, 34II, showed normal pairing (Fig. 1A–H), and confirmed the previous reports from Korea (Chung et al. 2017, 2018; Chung and Im 2020; Chung and Chung 2021). In this paper, the chromosome numbers of C. leucochlora Bunge, taxonomic synonym of C. breviculmis, were included (Table 1; Hoshino et al. 2011; Park et al. 2016). Further research is needed to clarify the chromosome variations of this species.
A meiotic chromosome number of n=34II was observed for C. brevispicula (Fig. 1I). The chromosome number is consistent with the previous report by Chung et al. (2023). The additional observation from another locality confirms that the species has a fixed chromosome number, which might suggest that the species is genetically structured. The species is endemic to Korea and is characterized by contracted achenes, long awned and pale green pistillate scales, and smooth perigynia (Nam et al. 2020).
This is the first report of chromosome number for C. candolleana, 2n=70 (Fig. 2A). The chromosome number is included in the chromosome number variation of C. breviculmis, which is taxonomically closely related to the species. The species is distributed in Korea and Japan (Park et al. 2016). In Korea, the species is distributed only in Jeju Island, and the species occurs in Honshu, Shikoku, Kyushu including Tsushima Islands in Japan (Masaki et al. 2010; Hoshino et al. 2011; Park et al. 2016).
C. conica is distributed in Korea and Japan (Hoshino et al. 2011; Park et al. 2016). Although the species is distributed in the whole area of Japan (Hokkaido, Honshu, Shikoku, Kyushu including Tsushima islands), the species occurs only in Jeju Island of Korea (Hoshino et al. 2011; Park et al. 2016). The chromosome numbers of the species are known as 2n=32, 33, 34, 36, 37, 38, 42 (Okuno 1940; Tanaka 1948; Hoshino and Okamoto 1979; Hoshino 1980, 1981; Hoshino and Waterway 1994). C. oshimensis Nakai (Izu islands, Tokyo prefecture, Japan) and C. atroviridis Ohwi var. scabrocaudata T. Koyama (Tokara islands, Kagoshima prefecture, Japan) are suggested to be the result of speciation from C. conica (Yano et al. 2010). C. conica complex has two phylogenetic types: type I with 2n=34, 36, 38 including C. atroviridis var. scabrocaudata and type II with 2n=32, 36, 38 including C. oshimensis and Carex sp. (Yano et al. 2010). Chromosome number for C. oshimensis and C. atroviridis var. scabrocaudata have not been reported. In the present study, we found a population with two chromosome numbers, n=18II and n=19II, from Jeju Island, Korea (Fig. 2B–D). With morphological characters, we were not able to distinguish between individuals with n=18II and n=19II sampled from the same population. C. multifolia Ohwi, a taxonomically closely related species, has been reported with various chromosome numbers 2n=30, 60, 62, 64, 65, 66, 70, 72 (Hoshino et al. 2011). Further investigations are required to understand morphological and cytological characteristics in the C. conica complex and closely related taxa.
C. fibrillosa is distributed in Korea, China, Japan, and Taiwan (Hoshino et al. 2011; Park et al. 2016). It is easy to find the species in sandy seashores. The species has long creeping rhizomes and distinct veins on the surface of perigynia (Hoshino et al. 2011). From Japanese populations, chromosome number records for the species were 2n=68 and n=34II (Tanaka 1948). We also found the same chromosome number and normal pairs in the meiotic metaphase I (Fig. 2E). The species is closely related with C. breviculmis (2n=54, 58, 62, 64, 66, 68, 70, 72, 74; Okuno 1939, 1940; Tanaka 1939, 1948; Hoshino 1981; Ohkawa and Yokota 1998; de Lange and Murray 2002; Chung et al. 2016, 2017, 2018; Chung and Im 2020; Chung and Chung 2021) and C. candolleana (2n=70). The lineage seems to have dynamic chromosome activities. Further investigation including phylogenetic and cytological investigation should be conducted to understand chromosomal speciation in the lineage.
From two populations of C. polyschoena, two different meiotic chromosome numbers were observed, n=34II and 36II, (Figs. 2F, G). Previous chromosome numbers vary, 2n=52, 72, 74, 76 (Chung et al. 2016, 2018; Chung and Im 2020; Chung and Chung 2021). The chromosome number of n=34II counted in the present study is a new number for the species. Although the species occurs throughout South Korea and is also found in Japan and China (Hoshino et al. 2011; Park et al. 2016), chromosome numbers of the species have been reported only from Korean populations. C. stenostachys Franch. et Sav., one of the closely related taxa, also has variation in chromosome numbers, 2n=56, 58, 59, 60, 61 (Hoshino et al. 2011). To understand cytological and morphological diversity in C. polyschoena, further study is required that encompasses the entire distribution area, including related taxa.
In the section, taxa with fixed and variable chromosome numbers were observed. Dynamic chromosomes have been postulated to explain great species diversity in Carex (Hipp et al. 2009). Further cytological investigations should be conducted to clarify chromosome variation in the section. In addition, cytological data analyses in a phylogenetic framework will help to understand diversity in Carex sect. Mitratae, one of the most specious sections in the genus.
The present research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF-2021R1I1A3060260).
Tomomi Masaki and Kyong-Sook Chung wrote the first version of the manuscript and Hyoung-Tak Im and Takuji Hoshino revised the manuscript several times. The final version was completed by the four authors. In addition, all the authors equally contributed to the field survey, taxonomic identification, and chromosome examinations and analyses for the present study.
