View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Kanazawa University Repository for Academic Resources Patterns of occurrence of hybrids of Castanopsis cuspidata and C. sieboldii in the IBP Minamata Special Research Area , Kumamoto Prefecture , Japan 著者 Kobayashi Satoshi, Hiroki Shozo journal or 植物地理・分類研究 = The journal of publication title phytogeography and toxonomy volume 51 number 1 page range 63-67 year 2003-06-25 URL http://hdl.handle.net/2297/48538 Journal of Phytogeography and Taxonomy 51 : 63-67, 2003 !The Society for the Study of Phytogeography and Taxonomy 2003 Satoshi Kobayashi and Shozo Hiroki : Patterns of occurrence of hybrids of Castanopsis cuspidata and C. sieboldii in the IBP Minamata Special Research Area , Kumamoto Prefecture , Japan Graduate School of Human Informatics, Nagoya University, Chikusa-Ku, Nagoya 464―8601, Japan Castanopsis cuspidata（Thunb．）Schottky and However, it is difficult to identify the hybrids by C. sieboldii（Makino）Hatus. ex T. Yamaz. et nut morphology alone, because the nut shapes of Mashiba are dominant components of the ever- the 2 species are variable and can overlap with green broad-leaved forests of southwestern Ja- each other. Kobayashi et al.（1998）showed that pan, including parts of Honshu, Kyushu and hybrids have a chimeric structure of both 1 and Shikoku but excluding the Ryukyu Islands（Hat- 2 epidermal layers within a leaf. These morpho- tori and Nakanishi 1983）．Although these 2 Cas- logical differences among C. cuspidata, C. sie- tanopsis species are both climax species, it is boldii and their hybrid can be confirmed by ge- very difficult to distinguish them because of the netic differences in nuclear species-specific existence of an intermediate type（hybrid）. Cas- markers（paper in preparation by the authors）. tanopsis cuspidata and C. sieboldii were re- Therefore, the morphology of the leaf epidermis garded to be varieties in the same species until is a useful key characteristic for the identifica- it was decided that C. sieboldii was a variety of tion of C. cuspidata, C. sieboldii and their hy- C. cuspidata（Nakai 1939 ; Yamanaka 1966）. brid. However, Yamazaki and Mashiba（1987 a, b）clas- Hiroki and Ichino（1991）reported that hybrids sified the 2 trees as separate species on the basis occurred in forests around the temples and of differences in nut shape and leaf epidermis. shrines of the Mikawa District of Aichi Prefec- Castanopsis cuspidata has a single-layered leaf ture and suggested that this hybridization was epidermis and bears small, globular nuts, caused by the planting of C. sieboldii in the C. whereas C. sieboldii has a 2-layered leaf epider- cuspidata distribution area. In 2001 we sug- mis and bears large, oblong nuts（Yamazaki and gested that, in the coastal areas of the Chubu Mashiba 1987 a）. District, hybrids may be growing in natural for- A type of nut or wood morphology that is in- ests because C. sieboldii coexists with C. cuspi- termediate between the 2 species is recognized data in these areas, although this hybrid origin （Kobayashi and Sugawa 1959 ; Yamanaka 1966 is questionable because of uncertainty about the ; Yamazaki and Mashiba 1987 a）. On the basis origin of the distribution of C. sieboldii（Hiroki of its wood anatomy, Kobayashi and Sugawa and Kobayashi 2001）. （1959）suggestedthattheintermediatetypewas To conduct a thorough examination of hybridi- a hybrid. However, Yamanaka（1966）considered zation in natural forests, we chose the Castanop- that the intermediate type was merely an intras- sis population in the Minamata Special Research pecific variation. By comparing its nut shape Area of the International Biological Program with the typical nut shape of each species, Hi- （IBP）, Kyushu. Although Tagawa（1973, 1979） roki and Ichino（1991）showed that individuals reported that only C. cuspidata is present in this withtheintermediatetypeofnutthatwere area, we had received information that C. sie- growing around temples and shrines in the boldii also exists there（personal communication Chubu District were hybrids of the 2 species. by Tagawa and Okubo in 1999）. We eventually － 63 － 植物地理・分類研究 第 51 巻第 1 号 2003 年 6 月 Table 1. The number of individuals of Castanopsis cuspidata, cuspidata, C.sieboldii and hybrids found in the investigated area Castanopsis cuspidata Castanopsis siboldii Hybrid total No. of individuals 147 105 64 316 found that both C. cuspidata and C. sieboldii are japonica,withEurya japonica in the shrub layer distributed in the area（Omura et al. 1978）. （Omura et al. 1978）. Therefore, we expected hybrids to be present too. The sampled leaves were transversely cross- We also intended to investigate the distribu- sectioned（30-μm thickness）with a plant mi- tion of the 2 species to see whether the hybrid crotome at the widest point of the leaf. The leaf population occurred only in the region where the epidermis was observed under a microscope（10 2 species overlapped. ×20 and 10×40）. Individuals with a leaf epider- mis of 1 layer, 2 layers, and both 1 and 2 layers Study site and methods were identified as C. cuspidata, C. sieboldii and In October 1999, we sampled leaves of Cas- the hybrid, respectively. All individuals sampled tanopsis from 316 individuals from the foothills were recorded on a topographic map（1 : 5000）. to the hilltops of the IBP Minamata Special Re- search Area（about 12 ha）（lat 32°30′N, long Results and discussion 131°35′E, 400―642 m a.s.l．）at Minamata in Ku- From our examination of the leaf epidermis, mamoto Prefecture, where mature forests re- we identified 147 plants as C. cuspidata, 105 as main in their natural state. In this area Cas- C. sieboldii and 64 as hybrids（Table 1）.Indi- tanopsis dominates the tree layer, accompanying viduals with a chimeric structure of both 1 and 2 Cyclobalanopsis gilva, C. salicina and Machilus epidermal layers within a leaf were identified as Fig. 1. Leaf epidermis of a hybrid between Castanopsis cuspidata and C. sieboldii. Black arrow indicates 1―layered leaf epidermis ; white arrow points to 2―layered leaf epidermis. Bar = 20 μm. － 64 － June 2003 J. Phytogeogr. Taxon. Vol. 51. No. 1 Fig. 2. Distribution of Castanopsis cuspidata, C . sieboldii and their hybrids in the IBP Minamata Special Research Area. hybrids（Fig. 1）. These results confirm the exis- influence for the same reason as described above. tence of C. sieboldii in the Minamata Special Re- In the Minamata Special Research Area, many search Area, as already recorded by Omura et al． C. cuspidata individuals were distributed on the （1978）, although Tagawa（1973, 1979）referred lower slopes or in the valleys, and their distribu- only to the presence of C. cuspidata.Ourresults tion was sparser at higher altitudes（Fig. 2）.In also show that hybrids occur in the inland areas contrast, C. sieboldii occurred mainly in higher of Kyushu where the 2 Castanopsis species coex- areas, such as on hilltops and ridges. These re- ist. Coexistence of C. cuspidata and C. sieboldii sults are consistent with the reports of iscommoninsouthernKyushu（Sako and Saida Yamanaka（1966, 1975）on Shikoku, in which 1990）, so one would expect hybridization of the 2 C. sieboldii was found to be distributed inland at species to occur widely. higher altitudes than C. cuspidata.IntheMi- Although we demonstrated that hybrids occur namata Special Research Area, only C. sieboldii in the natural forests of Kyushu, hybrids are is distributed on the hilltops and ridges. We as- largely due to human influence in inland Chubu. sume that C. sieboldii is more tolerant to This is because C. sieboldii is not naturally dis- drought stress or immature soils than C. cuspi- tributed in inland Chubu（Inami 1966）,and data. Hiroki and Ichino（1998）suggested that planted C. sieboldii are needed for hybrid forma- C. sieboldii may be able to establish itself more tion（Hiroki and Ichino 1991）. Yamada and successfully than C. cuspidata in such stressful Nishimura（2000）reported the coexistence of C. habitats as hilltops and ridges because larger cuspidata and C. sieboldii in the forests around nuts give more rapid early growth. temples and shrines in and around Okayama Hybrid occurrence is not confined to the zone Prefecture and referred to the existence of an in- where C. cuspidata and C. sieboldii meet. This termediate type of leaf epidermis. We presume suggests a long history of hybridization of the 2 that also these hybrids originate through human species. － 65 － 植物地理・分類研究 第 51 巻第 1 号 2003 年 6 月 Acknowledgments 15 : 257―277. We thank Dr. H. Tagawa（President of Kago- Omura, M., Miyata, I. and Hosokawa, T. 1978. shima Prefectural College, Kagoshima）and Dr. Biological production in a warm-temperate ev- K. Okubo（Shinshu University, Matsumoto）for ergreen oak forest of Japan. Kira, T., Ono, Y. providing us with information about the distri- and Hosokawa, T．（eds．）. JIBP synthesis Vol- bution of Castanopsis species in Minamata. We ume 18, pp.1―15. University of Tokyo Press, wouldalsoliketothankthelateMr.M.Nish- Tokyo. ioka（formerly Lecturer at Hyogo College of Sako, S. and Saida, M. 1990. Distribution maps Medicine, Nishinomiya City）for acting as our of Castanopsis cuspidata, C. cuspidata var. guide in the IBP Minamata Special Research sieboldii, Quercus gilva, Q. serrata and Cas- Area. tanea crenata in Kagoshima proper Pref. Bull. Kagoshima Univ. For. 18 : 125．（in Japanese） References Tagawa, H. 1973. An investigation of initial re- Hattori, T. and Nakanishi, S. 1983. Phytosoci- generation in an evergreen broadleaved forest ological system of the Camellietea japonicae of Minamata Special Research Area of IBP. I. Bull. Fac. Educ., Kobe Univ. 71 : 123―157． Seedling production and the distribution of （in Japanese with English summary） two dominant species. Rep. Ebino Biol. Lab., Hiroki, S.