The JapaneseSocietyJapanese Society forforPlant Plant Systematics ISSN OOOI-6799 Acta Phytotax. Geobot. 49 (2): 99-104 (1998) Chromosome Base Number of Coiylus (Betulaceae): Correction, and Evolution KAZUO OGINUMAi HIDETOSHI KAT02 and HIROSHI TOBE3 ' ithculty of Human Lijle and Enyironmental Seiences, Kochi Women's [Jhiversity, Kochi 780-8515, 2Makino Japan; Herbarium, thculty ofScience, 7bkyo Metropolitan Uhiversity, Hl chioji, Tokyo, "Flaculty 192-0364, Japan; of integrated Human Studies, K),oto Vhiversity, 1<Yoto 606-8501, Japan Abstract. The chromosome base number of Corytus (15 species) has long been considered to be x=14 on the basis of the early report of Woodworth, but in later publieations different chromosome nurnbers have been reported in most species of the genus. This paper, on the basis of review of the earlier publications and additional observations in three species of Ceryltts (C. americana, C, heterqphylla var, thunbergii, C. sieboldiana), demonstrates that the generic chromosome base number is not x=14 but x=11. Molecular phylogeny of Betulaceae (published elsewhere in this issue) suggests that x=11 is an autapomorphy of Corylus derived from x=8 common to three other genera of Coryloideae. Key words: Betulaceae, chremosome number, CoTyloideae, Corylus, evolution Received September 11, 1998; accepted January 4, 1999 The family Betulaceae is well known cytologically, and all the six genera have been studied with respect to their gametic andlor somatic chromosome numbers. The generic chromosome base number is determined as x=14 for Alnus and Betula and x=8 for Carpinus, Ostrlya, and Ostryopsis (see Johnson and Wilson, 1993). Concerning the remaining genus Corylus, 14 of the 15 species are known cytologically, and its chromosome base number has usually been considered to be x=14 (e.g., Bousquet et at., 1992; Johnson and Wilson, 1993; Takhtajan, 1997). "all Furlow (1990, p. 65) describes that investigated species of Corylus have chromosome numbers of 2n=28." The report of n= 14, however, appears only in a paper of Woodworth (1929, 11 species), that of 2n=28 in a paper of Mehra (1976, Corytus colurna), and those of various chromosome numbers such as n==6, 7-10, 11, 10-12, and 2n=18 and 22, instead of n=14 or 2n=28, in the other publications (Table 1). Noticeably, 2n==22 is the commonest number in the publications after Woodworth. These facts have made us doubt x==14 of Coryl"s and to reinvestigate several species of the genus to clarify an exact generic chromosome base number. Materials and Methods Three species of CoT:ylus, i.e., C. americana Walt. (voucher: Tbbe & Oginuma 288), C. heterqphylla Fischer var. thunber:gii Blume (voucher: NII-Electronic Library Service The JapaneseSocietyJapanese Society forforPlant Plant Systematics 100 Acta Phytotax. Geobot, Vol. 49 TABLE 1, A summaTy of chromesome data in Corytus Woodwerth Pr¢ $entstudy Taxon (1929) Other authorsi> Cerytus americana MM. n=14n=:14n=14nv14 n==6n::1e,11,M 2n==222n=222nm18,22,282n==22 C. aveUana L. C, col"rna L. n=7-10n=:6 C. cornuta Marsh 2n=222n==222nrt222n= C. farox Wallich C. heterophylla Fisch. n==14 2n:=22 C. hostrata Ait, n=11 222n==222n==22 C Zolurneides Schneider C. maxima Mill. n==14n=14n=t14n=14n=:14n==14n=11 C, pontia C, Koch C, sieboldiana Blume 2n=22 C. spinescens Rehd, C. tibetica Betalin 2n=22 C. vilinorinii Rehd. i)Data "Index from Fedorov (1974), and to Plant Chromosome Numbers7' edited by Moore (1973-1977>, Goldblatt <1981L1988) and Goldblatt and Johnson (1990-1,993). Tbbe 309) and C. sieboldiana Blume (voucher: Tbbe & Oginuma 291) cultivated at Kamigamo Experimental Forest Station of Kyoto University, were investigated in this study. Somatic chromosomes were examined using young leaves and on the basis of at least five cells for each species. Methods of sampling, pretreatment, fixation, maceration, and staining for cytological study were described elsewhere (Oginuma et al., 1992). The categories of chromosomes follow Levan et al. (1964) and were described on the basis of the position of centromeres. Results and Discussion All the three species examined, i.e., Corylus americana (Figs. 1, 2), C. heterophylta var. thunbergii (Figs. 3, 4), and C. sieboldiana (Figs. 5, 6), have 2n=22 in 11 pairs. Their karyotypes at mitotic metaphase, which were observed for the first time for the genus, are nearly identical in the three species. The length of 22 chromosomes varies gradually and ranges from about 0.5ptm to 1.7gm. Of the 22 chromosomes, six chromosomes constituting the first and the second longest pair and a medium-sized pair have centromeres at submedian position, and the remaining 16 chromosomes in eight pairs have thern at median position. The secondary constrictions are observed in the proximal regjons of the short arms in the first longest pair of chromosomes. Based on the three species examined, the somatic karyotype is apparently consistent in the genus Corlylus and comprises 22 chromosomes in 11 pairs. In Table 1 all the chromosome information available until NII-Electronic Library Service The JapaneseSocletyJapanese Society forforPlantSystematlcs Plant Systematics December 1998 OGINUMA et alChromosomes of Coi)Jlus 101 be ' igag ' '' ･ el･ '･X,i･ g s･,/si $l,ljee#lkge.f,si/Ylk ijge ts ts lj ee"' X ' tw11'' / pa ,1ts11j,11l,agim/ I,1eess#,ti1esk,ecik FiGs 16 Somatic chiomosomes at metaphase in Cor]Jl"s 1-2 C amertcana (2n==22) 3-4 C heterophytta var thunbergti (2n==22) 5-6 C sleboJdiana (2n=22) Arrowheads indicate chTomosomes with a secondary constnctien Arrows mdicate chromosomes having centromeres at submedian posmon Figs 2, 4, and6are respective drawmgs of Figs 1, 3, and5 Scale=2ptm NII-Electronic Library Service The JapaneseSocietyJapanese Society forforPlant Plant Systematics 102 Acta Phytotax. Geobot. Vol, 49 now is presented, Apart from the report of Woodworth (1929), ll of 14 species whose chromosome numbers have been counted all have either or both n==11 or 2n==22. Thus, contrary to the traditional idea, the base number of Corylus ought to be corrected as x== 11, and not x=14. The phylogenetic relationship of Betulaceae has been just clarified together with Ticodendraceae and Casuarinaceae using Nbthojbg"s as outgroup on the basis of matK gene sequence data (Kato et al., 1998). It TABLE 2.A summary of chromosorne data and base numbers in genera of Betulaceae SubiamilylTribeVGenusi) Chromosome data (n) Base number (x) Betuloidette Betuleae Alnus 74) 142)3)S) 212)]) 2s2)])S) s62)]}S) or) 14 ) : ] : (7 Betuta 142)3)5),212)3),243),2s2)3)S),312).322),3s2)3),422)3)14 Coryloideae Carpineae Cau)in"s 8Z}3)S),l.62)3),322)3)5) 88 Ostrya s2)3)5) Coryleae Corylus 63),7-123),112)3)S),142)3) 118 Ostryopsts s2)s) i)CIass'ification follows Furlow (1990). 2)Data from Fedorov (1974) 3}Data "Index frorn to Plant Chromosome Numbers" edited by Moore (1973-1977), Goldblatt (1981-1988) and Goldblatt and Sohnsen (1990-1993), `)Data from Chiba (1962)･ S)Data from the pTesent study or unpublished data, Ainus {xtl4) Betula {x=14) Carpinus (xics) Betulaceae Osttya (xirs) Cot3tlus (x=m OStTYopSiS (X=8) "codendron (x=13) Ticodendraceae Casuarina Casuarinaceae Nothofagaceae Notholagus FIG. 7, Evolution of generic chromosome base numbers in Betulaceae. Phylegenetic tree is from Kato et al. (1998; this vo]urne) where a monophyly of Betulaceae and sister-group Telationship between Betulaceae and Ticedendraceae are strengly supported. An arrow indicates an evolution ofx=11. NII-Electronic Library Service The JapaneseSocietyJapanese Society forforPlant Plant Systematics December 1998 OGINUMA et al.: Chromosomes of Coryltcs 103 can be summarized as follows: Betulaceae (comprising six genera Ainus, Betula, Carpinus, Corylus, Osttlya, and Ostcyopsis) are monophyletic and sister to Ticodendraceae; Betulaceae are divided into two clades, one comprising Alnus and Betula (as Betuloideae) and the other comprising the remaining four genera (as Coryloideae); the latter clade is further divided into two subclades, the Corylus-Ostryopsis clade and the Carpintts-Ostrya clade (Fig. 7). Since chromosome base numbers of all the six genera of Betulaceae have become clear (Table 2), their evolution can be discussed in the light of the phylogenetic tree. However, since Betulaceae have a common chromosome base number neither with the sister group Ticodendraceae (x=13, Snow and Goldblatt [1992]) nor with Casuarinaceae (x =8 in Gymnostoma, a most primitive genus of the family [Johnson and Wilson, 1989]), it is uncertain which is an ancestral base number of the family, x=8, 11 (Coryloideae) or x=(7 or) 14 (Betuloideae). Irrespective of familial base number, however, x=8 is obviously a plesiomorphy of Coryloideae because it is common to both the Cor:yltLs-Ostryopsts clade and the Carpinus-Ostrlya clade. The x==11 of Corytus is an autapomorphy derived from x=8. We are. to Hiroyuki Tanaka for their assistance in collecting materials used in grateful this study, References Bousquet, J., S. H, Strauss and P. Li. 1992. Complete congruence between morphological and rbcL-based molecular phylogenies in Birches qrld related species (Betulaceae). Mol. Biol. Evol, 9: 1076-1088, Chiba, S. 1962. Studies on the breeding of Betula andAinus species. (1) On the differences of morphological characters and chromoseme number between Alnus and Alnus hirsuta hirsuta var, microphyUa. J, Jap. Forest Soc. 44: 237-243. Fedorov, A. A, 1974. Chromosome Numbers of Flowering Plants. English ed, Otto Koeltz, Koeningstein. Furlow, J, J. 1990, The genera of Betulaceae in the Southeastern United States, J. Arnold Arb. 71: 1-67, Goldblatt, P. 1981-1988, Illdex to Plant Chromosome Numbers, Volumes for 1975-1978, 1982-1983 and 1984-1985 published in 1981, 1985 and 1988, respectively. Monogr. Syst. Bot, Missouri Bot, Gard. 5: 1-553; 13: 1-224, 23: 1-264. and D, E. Johnson.