Chromosome Botany (2007) 2: 87-91 © Copyright 2007 by the International Society of Chromosome Botany Intraspecific polyploidy of Houttuynia cordata and evolution of chromosome number in the Saururaceae Kazuo Oginuma1,8, Hisako Sato2, Yoshiko Kono2, Shaotien Chen3, Zuken Zhou3, Ching-I. Peng4, Arata Momohara5, Tomohisa Yukawa6 and Hiroaki Setoguchi7 1Department of Environmental Science, Faculty of Human Life and Environmental Science, Kochi Women’s University, Eikokuji-cho 5-15, Kochi 780-8515, Japan; 2Graduate School of Human Health Science, Kochi Women’s University, Eikokuji-cho 5-15, Kochi 780-8515, Japan; 3Department of Phytotaxonomy and Phytogeography, Kunming Institute of Botany, The Chinese Academy of Sciences, Heilongtan, Kunming 650204, Yunnan, The People’s Republic of China; 4Herbarium (HAST), Research Center for Biodiversity, Academia Sinica, Taipei 115, Taiwan; 5Faculty of Horticulture, Chiba University, Matsudo, Chiba 271-8510, Japan; 6Tsukuba Botanical Garden, National Science Museum,Tsukuba-shi, Ibaraki 305-0005, Japan; 7Department of Biology, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida Nihonmatsu-cho, Sakyo-ku, Kyoto-shi, Kyoto 606-8501, Japan 8Author for correspondence ([email protected]) Received July 19, 2007; accepted August 25, 2007 ABSTRACT. Intraspecific polyploidy and cytogeography were clarified in the samples of Houttuynia cordata (Saururaceae) studied in the Sino-Japanese region of eastern Asia, ranging from Nepal, China, northern Thailand, Taiwan to Japan. Five chromosome numbers of 2n=72, 80, 96, 112 and 128 were detected, four of which were firstly recorded here. These chromosome numbers suggested that the basic chromosome number of Houttuynia could be x=8. The observed cytotypes were evaluated as 2n=72, 80, 96, 112 and 128, and represented 9x, 10x, 12x, 14x, and 16x, respectively. The continental part of east Asia harbored intraspecific polyploidy ranging from 9x to 16x, and only one cytotype of 12x or 2n=96 was found from the eastern edge of the Asian continent between Taiwan and Japan. The evolution of basic chromosome number was discussed based on a phylogenetic tree of the Saururaceae, suggesting that x=11 was an archaic basic chromosome number in this family. Houttuynia may have experienced a disploid reduction from x=11 to x=8, as an autoapomorphy and subsequent intraspecific polyploidization in continental eastern Asia. KEYWORDS: Chromosome, Eastern Asia, Houttuynia cordata, Saururaceae, Sino-Japanese region Houttuynia Thunb. is monotypic and a member of the the wide distribution of this species: n=48 (Japan, Mihara Saururaceae together with three other genera of Anemopsis, 1960), 2n=24 (Taiwan, Hsu 1968), n=52-56 (Japan, Shibata Gymnotheca and Saururas (The Angiosperm Phylogeny and Miyake 1908), 2n=ca. 96 (Japan, Okabe 1934; Nepal, Group [APG II] 2003). Phylogenetic relationships of Kurosawa 1966), 2n=96 (Japan, Okada 1986), and these four genera have been reported based on DNA 2n=100-104 (unknown location, Soderberg 1927). The sequence data; however, the phylogenetic position of long range of H. cordata in the Sino-Japanese region, Houttuynia conflicts in the organelle and nuclear DNA covering over 5000 km, suggests that migration and trees (Meng et al. 2002, 2003). Chloroplast (cp) and intraspecific evolution of H. cordata may have occurred mitochondrial (mt) DNA sequence data suggest that separately in several areas. Intraspecific diversity and Houttuynia is sister to Anemopsis, whereas nuclear (n) geographic structure of chromosome number are expected DNA suggests that Houttuynia is sister to the Saururus- along the corridor in the Sino-Japanese region. Gymnotheca clade. The basic chromosome number of Houttuynia is Houttuynia cordata Thunb., only the species in the controversial, as is the Saururacean chromosome number. genus, is a perennial herb mainly distributed in the Sino- The basic chromosome number of Houttuynia is thought Japanese region of eastern Asia, ranging from Japan to to be x=12 (Okada 1986), while the basic number is x=22 the Himalayas through the Ryukyu Islands, Taiwan, and or 11 (2n=44) in Anemopsis, x=9 (2n=18) in Gymnotheca, China, and extending to southeast Asia. In Japan, the and x=11 (2n=22) in Saururas. Based on variation in species propagates by formation and separation of chromosome number within Houttuynia, the basic chro- underground stems and by parthenogenesis (Shibata and mosome number should be redetermined to understand Miyake 1908; Mihara 1960), whereas reproduction by the evolution of chromosome number in the Saururaceae, sexual reproduction has not been reported. The reproduc- a paleoherb group, i.e., to determine the plesiomorphic tive characteristics of parthenogenetic and microspore characteristic of chromosome number in this paleoherb degeneration are widely accepted (e.g., Mabberley 1998). family. Various chromosome numbers have been reported from Here we present intraspecific polyploidy with new 87 88 OGINUMA ET AL. chromosome data in H. cordata collected from Japan, 3) 2n=96 One plant each collected in Southeast China Nepal, Thailand, The People’s Republic of China and (Figs. 4 and 9 [collection site 11], Table 1) and Japan Taiwan. We examined the presence or absence of chromo- (Figs. 5 and 9 [collection site 14], Table 1) and four plants some number diversity and discuss its cytogeographical collected from two localities in Taiwan (Figs. 6 and 9 aspects, in addition to discussing chromosome evolution [collection sites 12 and 13], Table 1) showed 2n=96. This in the Saururaceae by combining our original data and chromosome number confirms previous reports (Mihara previously published data. 1960; Okada 1986). MATERIALS AND METHODS The localities where H. cordata individuals were collected are shown in Table 1. Individual plants were collected in the field and cultivated in the greenhouse, Kochi Women’s University, Japan. The pretreatment, fixation, and chromosome-staining methods were described elsewhere (Oginuma and Nakata 1988). Voucher specimens were deposited in the Herbaria of Kyoto University (KYO) and Academia Sinica, Taipei (HAST). The evolutionary trend of basic chromosome number in the Saururaceae was estimated using the ACCTRAN transformation in MacClade version 3.05 (Maddison and Maddison 1992), based on the Saururacean phylogeny (Meng et al. 2003). RESULTS AND DISCUSSION Somatic chromosome numbers at metaphase in the plants collected in 14 localities were 2n=72, 80, 96, 112 and 128. Those chromosomes showed gradual variation in length, ranging from 0.6-1.6 µm (Figs. 1-8). 1) 2n=72 The ten plants collected in five localities in China (Figs. 1 and 9 [collection sites 5-8 and 10], Table 1) and two plants collected from Thailand (Figs. 2 and 9 [collection site 3], Table 1) were 2n=72, that was the first Figs. 1-8. Somatic chromosomes at metaphase for record of this chromosome number for this species. intraspecific polyploidy determination of Houttuynia cordata. 1. 2n=72 (Jin Tou, China). 2. 2n=72 (Chiang 2) 2n=80 One plant collected from Teng Chon, Yunnan Mai, Thailand). 3. 2n=80 (Teng Chong, China). 4. 2n=96 (Chong Zuo, China). 5. 2n=96 (Kochi, Japan). 6. 2n=96 County, China, was 2n=80 (Figs. 3 and 9 [collection site (Yangming Shan, Taiwan). 7. 2n=112 (Kakani, Nepal). 8. 4]), that was reported here for the first time. 2n=128 (Teng Chong, China). Scale = 2 µm. Table 1. Chromosome number of Houttuynia cordata and its collections Chromosome No. of plants Collections number observed 2n=72 China. Yunnan County, ca. 15 km south from Gong Shang. S.Chen & H. Setoguchi 2004073 (KYO) 2 China. Yunnan County, near FuGong, south of Gong Shang. S. Chen & H. Setoguchi 2004074 (KYO) 2 China. Yunnan County, Gong Shang, S. Chen & H. Setoguchi 2004063G (KYO) 2 China. Yunnan County, Xinxian Xiang - Wan Fou Jian. H. Setoguchi et al. 2004378 (KYO) 2 China. Yunnan County, Jin Tou. H. Setoguchi et al. 200611(KYO) 2 Thailand. Chiang Mai, Queen Sirkit Bot. Gard. H. Funakoshi s.n. in 2006 (KYO) 2 2n=80 China. Yunnan County, Tengchong. H. Setoguchi et al. 200410 (KYO) 1 2n=96 Taiwan. Taipei County, Chingshan Waterfall. H. Setoguchi 04T-M1905 (KYO) 2 2n=96 Taiwan. Taipei County, Yangmingshan. Oginuma 0602 (KYO) 2 2n=96 China. Guangxi Zhuangzu Zizhiqu, Chong Zuo Shi. Peng 19746 (HAST) 2 2n=96 Japan. Kochi City. Oginuma 0601 (KYO) 2 2n=112 Nepal. Kathmandu County, Godawari. Oginuma 0602 (KYO) 2 2n=112 Nepal. Nuwakot County, Kakani. Oginuma 0603 (KYO) 2 2n=128 China. Yunnan County, Pin Bian. H. Setoguchi 2004389 (KYO) 2 2n=128 China. Yunnan County, Tengchong. H. Setoguchi et al. 200410 (KYO) 1 INTRASPECIFIC POLYPLOIDY OF HOUTTUYNIA CORDATA 89 Fig. 9. Cytogeographical distribution of intraspecific polyploidy in Houttuynia cordata. 1. Kakani, Nepal (2n=112). 2. Godawari, Nepal (2n=112). 3. Chiang Mai, Thailand (2n=72). 4. Teng Chong, China (2n=80, 2n=112). 5. Jin Tou, China (2n=72). 6. Fu Gong, China (2n=72). 7. Southern Fu Gong, China (2n=72). 8. Gong Sahan, China (2n=72). 9. Pin Bian, China (2n=128). 10. Xingxian Xiang, China (2n=72). 11. Chang Zuo, China (2n=96). 12. Yangming Shan, Taiwan (2n=96). 13. Ching Shan waterfall, Taiwan (2n=96). 14. Kochi, Japan (2n=96). 4) 2n=112 Four plants collected from two localities in South China, whereas the cytotype of 2n=112 plant was Nepal showed 2n=112 (Figs. 7 and 9 [collection sites 1 found in Nepal and that of 2n=72 plant was found in and 2], Table 1), that was reported here for the first time. north Thailand. The chromosome number of 2n=ca. 96 was reported earlier in Nepal plants (Kurosawa 1966). 5) 2n=128 Three plants collected in two localities in The individual with the chromosome number of 2n=96 China were 2n=128 (Figs. 8 and 9 [collection sites 4 and may be distributed widely throughout the Sino-Japanese 9], Table 1), that was reported here for the first time. region from the Himalayas to Japan down to South China Houttuynia cordata showed here five different chro- and Taiwan.