© 2021 The Japan Mendel Society Cytologia 86(2): 109–112

Invited Review:

Chromosomal Divergences in the Genus () Distributed in Japan

Kyoko Sato*

Faculty of Science, Academic Assembly, University of Toyama, 3190 Gofuku, Toyama 930–8555, Japan

Received March 24, 2021; accepted March 31, 2021

Summary Chromosomal information is important for taxonomic grouping and provides insight into the origin of and taxonomic relationships between taxa. Studies on the karyotype and chromosomal diversity of Taraxacum can lead to a better understanding of the , phylogenetic taxonomic relationships, and diversities of the species in the genus. The present review focuses on the chromosomal divergences in the genus Taraxacum dis- tributed in Japan from the viewpoint of cytotaxonomy.

Keywords Cytotaxonomy, Taraxacum, Asteraceae, Polyploid complex, Karyotype, Chromosome number.

The genus Taraxacum Weber ex F. H. Wigg. (Astera- polyploid are mostly obligatory but sometimes ceae) consists of perennial herbs distributed around the facultatively agamospermous (Richards 1970, Grant world, especially in the Northern Hemisphere (Ohwi and 1981). In apomicts, fertilization and meiosis are usually Kitagawa 1992). The genus includes ca. 60 species that circumvented, and the new generation of plants arising are further subdivided into 1,600–2,500 apomictic lines from seeds developed from the unreduced megaspores (Mabberley 2017). Makino and Nemoto (1931) classi- of the mother plant without fertilization leads to the fied native Japanese Taraxacum into five species and formation of a clone population because all offsprings one variety: T. albidum Dahlst., T. ceratophorum DC., of polyploid Taraxacum are genetically identical to their T. japonicum Koidz., T. longe-appendiculatum Nakai, T. mother plants (Bhojwani and Bhatnagar 2008). platycarpum Dahlst. and T. platycarpum var. rubicunda Typically, the number of chromosomes is the same Nakai. Based on exhaustive taxonomical studies, native in all individuals within a given species. However, Japanese Taraxacum was found to comprise 22 species, plants with different chromosome numbers are frequent- four varieties, and eight forms according to Kitamura ly found within the bounds of one taxonomic species. (1957), or 21 species, three varieties, and four forms One reason for this is that normal meiosis does not occur according to Ohwi and Kitagawa (1992). On the other when gametes are formed, and unreduced gametes with hand, Morita (1995) classified the genus into 15 spe- the same chromosome number as that of somatic cells cies, two subspecies, and one variety, which were later are formed before fertilization occurs. Another reason modified to 14 species, one subspecies, and two variet- is that simultaneous crossing between genomically dif- ies (Morita 2017), based on ploidy levels and breeding ferentiated individuals and chromosome polyploidiza- systems. Meanwhile, Serizawa (1986, 1995) grouped tion within a species yields normal meiotic polyploids. the native lowland diploid Taraxacum as two species In order to better understand this phenomenon, cyto- (T. platycarpum and T. maruyamanum) (Fig. 1A, B), taxonomical surveys based on chromosome techniques and later proposed a different classification of Japanese are most useful. The number, shape, and behavior of Taraxacum species (Serizawa 2006). Japanese native chromosomes are of great value in taxonomy. Chromo- dandelions are thus fraught with taxonomic complexity. somal information is important for taxonomic grouping Besides the native Taraxacum species, two similar and provides insight into the origin of and taxonomic introduced species thrive in Japan, T. officinale Weber relationships between taxa, as well as basic data needed ex F. H. Wigg. and T. laevigatum (Willd.) DC., which to conserve biodiversity. Such information also makes are distinguished by differences in their achene color it easy to find useful strains rich in active ingredients (Osada 1972, Morita 2017). They belong to a monobasic and perform efficient breeding for horticultural plants. genus with x=8 (Darlington and Wylie 1955, Fedorov Studies on the karyotype and chromosomal diversity 1969). Diploid plants (2n=2x=16) are sexual, whereas of Taraxacum can lead to a better understanding of the taxonomy, phylogenetic taxonomical relationships, and * Corresponding author, e-mail: [email protected] diversities of the species in the genus. DOI: 10.1508/cytologia.86.109 The focus of this review is to outline the chromosomal 110 K. Sato Cytologia 86(2)

Fig. 1. Natural habitat of Taraxacum distributed in Japan. A) T. platycarpum. B) T. maruyamanum. C) T. albidum. D) T. denudatum. E) T. shikotanense. F) T. officinale s.l. divergences in the genus Taraxacum distributed in reported that chromosome pairings in PMCs of lowland Japan, from the viewpoint of plant cytotaxonomy. diploid species (including T. maruamanum) were nor- Osawa (1913) was the first to conduct a cytological mal, i.e., having only eight bivalents in the first meta- study on Japanese Taraxacum species. Subsequently, phase of meiosis. Yamaguchi (1986) reported that almost their chromosome numbers and cytological features all diploid species could be hybridized artificially, and were revealed by Miyaji (1932), Matsuura and Sutô concluded that local isolation due to differences in habi- (1935), Okabe (1934, 1951), Takemoto (1954, 1956, tat preference played an important role in the speciation 1961, 1970), Nishioka (1956), Yamaguchi (1974a, b, of Japanese diploid Taraxacum species. These findings 1976a, b, 1986), Nishikawa (1984), Akhter et al. (1993), may help establish a more unified view of the taxonomic Sato et al. (2007a, b, c, d, 2008, 2011, 2012a, b, 2014, treatment of diploid dandelions. 2015, 2019, 2020), and Miura et al. (2012). Meanwhile, other studies have shown that there is Diploid species of Taraxacum have similar karyotypes karyotypic variation among some Japanese agamosper- involving two pairs of chromosomes with satellites, mous species including infraspecific cytotype variation except for T. maruyamanum which has one pair of satel- (Akhter et al. 1993, Sato et al. 2007c, d, 2008, 2011, lite chromosomes (Yamaguchi 1974a, 1986, Sato et al. 2014, 2019, 2020). Recently, several agamospermous 2007a). No karyotypic variation has been detected with- dandelions have been shown to exhibit infraspecific in the respective diploid species (Nishioka 1956, Take- cytotype variation in Japan. Akhter et al. (1993) ob- moto 1961, Yamaguchi 1974a, 1986, Sato et al. 2007a). served three polyploid numbers of 2n=24, 32, and 40 Although Morita (1995, 2017) described T. ohirense S. in T. hondoense. Additionally, polyploid complexes in Watan. et Morita to be an alpine diploid species in Japan, several Japanese branches of the genus Taraxacum have its chromosome number was not reported. Among sex- been analyzed cytotaxonomically by Sato et al. (2007b, ual diploid dandelions, only T. maruyamanum differs in c, d, 2008, 2011, 2014, 2019, 2020). The taxonomic spe- the number of satellite chromosomes. Sato et al. (2007a) cies T. albidum (Fig. 1C) and T. denudatum (Fig. 1D) 2021 Chromosomal Divergence of Taraxacum in Japan 111 include tetraploids and pentaploids, respectively (Sato Ann. Rep. Hakusan Nat. Conserv. Cent. 39: 1–4. (in Japanese) et al. 2011, 2019), whereas T. shikotanense (Fig. 1E) Miyaji, Y. 1932. On the chromosome numbers in the genus Taraxa- cum. Bot. Mag. Tokyo 46: 406–408. (in Japanese) comprises a polyploid series (hexaploid to undecaploid) Morita, T. 1995. Taraxacum. In: Iwatsuki, K., Yamazaki, T., Boufford, (Sato et al. 2020). 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