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Cytology of Thirteen Taxa in the Genus Isodon (Lamiaceae: Nepetoideae) from China

国产香茶菜属十三个分类群的细胞学研究



全 文 :国产香茶菜属十三个分类群的细胞学研究∗
向春雷1ꎬ 陈亚萍1ꎬ2ꎬ 船本常男3∗∗ꎬ 彭  华1
(1 中国科学院昆明植物研究所东亚植物多样性与生物地理学重点实验室ꎬ 云南 昆明  650201ꎻ 2 中国科学院大学ꎬ
北京  100049ꎻ 3 日本昭和药科大学ꎬ 药学基础教育与研究中心ꎬ 日本 东京  194 ̄8543)
摘要: 对国产 11种 2变种共 16个居群的香茶菜属植物的染色体数目进行了研究ꎮ 除线纹香茶菜细花变种
以外ꎬ 其它种类的染色体数目均为首次报道ꎮ 研究结果表明ꎬ 有 12个物种为二倍体ꎬ 其染色体数目均为
2n= 24ꎬ 推测该属植物的染色体基数为 x= 12ꎮ 而细锥香茶菜既有染色体数目为 2n = 24 的居群ꎬ 也存在
2n= 48的居群ꎬ 表明该种为二倍体或四倍体ꎬ 同时 2n= 48的染色体数目也是香茶菜属内的首次报道ꎮ
关键词: 染色体数目ꎻ 横断山脉ꎻ 香茶菜属ꎻ 多倍体
中图分类号: Q 942            文献标识码: A                文章编号: 2095-0845(2014)05-561-08
Cytology of Thirteen Taxa in the Genus Isodon
(Lamiaceae: Nepetoideae) from China
XIANG Chun ̄Lei1ꎬ CHEN Ya ̄Ping1ꎬ2ꎬ Tsuneo FUNAMOTO3∗∗ꎬ PENG Hua1
(1 Key Laboratory for Plant Diversity and Biogeography of East Asiaꎬ Kunming Institute of Botanyꎬ Chinese Academy
of Sciencesꎬ Kunming 650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ Chinaꎻ
3 Biological Instituteꎬ Fundamental Education and Research Center of Pharmaceutical Sciencesꎬ
Showa Pharmaceutical Universityꎬ 194 ̄8543 Tokyoꎬ Japan)
Abstract: This paper reports the chromosome numbers of 11 species and two varieties of Isodon from 16 populations
in China. For all taxa except I􀆰 lophanthoides var. graciliflorusꎬ chromosome numbers are reported here for the first
time. All taxa are counted as diploid (2n= 24): I􀆰 albopilosusꎬ I􀆰 coetsaꎬ I􀆰 flabelliformisꎬ I􀆰 forrestiiꎬ I􀆰 gesneroidesꎬ
I􀆰 lophanthoides var. graciliflorusꎬ I􀆰 oreophilus var. elongatusꎬ I􀆰 parvifoliusꎬ I􀆰 pleiophyllusꎬ I􀆰 polystachysꎬ I􀆰 racemosusꎬ
I􀆰 scopariusꎬ and I􀆰 weisiensis. Thusꎬ x= 12 is inferred as the basic chromosome number of Isodon. In additionꎬ the
chromosome number 2n= 48ꎬ which is newly recorded for the genusꎬ is also reported in one population of I􀆰 coetsaꎬ
indicating the species to be diploid and tetraploid.
Key words: Chromosome numberꎻ Hengduan Mountainsꎻ Isodonꎻ Polyploidy
  Isodon (Schrad. ex Benth.) Spach (Lamiaceae)
was segregated as an independent genus from the no ̄
toriously heterogeneous Plectranthus L′Hér. (Spachꎬ
1840ꎻ Kudôꎬ 1929ꎻ Coddꎬ 1968ꎬ 1984ꎬ 1986) based
on a combination of morphological characters: pedun ̄
culate and bracteolate cymesꎬ 4 / 1 ̄bilabiate corolla
limbs ( four lobes on the upper lip and one lobe on
the lower)ꎬ equally or subequally 5 ̄toothed or 3 / 2 ̄
bilabiate calycesꎬ and free filaments inserted at base
of corolla tube (Liꎬ 1988ꎻ Li and Hedgeꎬ 1994ꎻ Har ̄
植 物 分 类 与 资 源 学 报  2014ꎬ 36 (5): 561~568
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201413237

∗∗
Funding: Knowledge Innovation Project of the Chinese Academy of Sciences (KSCX2 ̄EW ̄J ̄24ꎬ KSCX2 ̄EW ̄Z ̄1)ꎬ National Natural Sci ̄
ence Foundation of China (31270245ꎬ 31110103911)ꎬ and State Key Laboratory of Systematics and Evolutionary Botanyꎬ Institu ̄
te of Botanyꎬ Chinese Academy of Sciences (LSEB2012 ̄08)
Author for correspondenceꎻ E ̄mail: funamoto@ac􀆰 shoyaku􀆰 ac􀆰 jp
Received date: 2013-12-12ꎬ Accepted date: 2014-04-24
作者简介: 向春雷 (1984-) 男ꎬ 博士ꎬ 副研究员ꎬ 主要从事植物分类与系统发育研究ꎮ E ̄mail: xiangchunlei@mail􀆰 kib􀆰 ac􀆰 cn
ley et al.ꎬ 2004). As currently circumscribedꎬ the ge ̄
nus Isodon comprises ca. 100 species distributed in
tropical to temperate East Asia and tropical Africa
(Coddꎬ 1984ꎻ Liꎬ 1988ꎻ Li and Hedgeꎬ 1994ꎻ Mab ̄
berleyꎬ 2008)ꎬ of which 80 species have been repor ̄
ted from China (Liꎬ 1988ꎻ Li and Hedgeꎬ 1994). Most
of these species are geographically restricted to the
Southwestern Chinaꎬ which is considered as the di ̄
versity center of the genus ( Zhong et al.ꎬ 2010ꎻ
Xiang and Liuꎬ 2012ꎻ Chen et al.ꎬ 2014).
The value of cytological data in the study of
plant evolutionꎬ diversification and phylogeny has
long been recognizedꎬ and chromosome cytology is
considered as important evidence in resolving rela ̄
tionships among the mint family ( Bushnellꎬ 1936ꎻ
Elena ̄Rosellóꎬ 1981ꎻ Gillꎬ 1983ꎻ Cantinoꎬ 1985ꎻ
Funamotoꎬ 2007ꎻ Funamoto et al.ꎬ 2008ꎬ 2009ꎻ
Funamoto and Smirnovꎬ 2011). Despite the poten ̄
tial systematic importance of chromosomal data for
Isodonꎬ the genus is cytologically poorly studied
(Table 1). The first published account of chromo ̄
somal data in Isodon can be traced back to 1950
when Suzuka (1950) reported the chromosome num ̄
ber of Plectranthus japonicus (Burm. f.) Koidz [ =
I􀆰 japonicus ( Burm. f.) H. Hara] to be 2n = 24.
Wakabayashi (1973) identified 2n= 24 for Rabdosia
umbrosa (Maxim.) H. Hara var. hakusanensis (Kudô)
H. Hara [ = I􀆰 umbrosus ( Maxim.) H. Hara var.
hakusanensis (Kudô) K. Asano]ꎬ and Sokolovskaya
et al. (1986) reported 2n = 24 for both I􀆰 japonicus
and I􀆰 excisus ( Maxim.) Kudô. In his cytological
study of the flora of Cameroons Mountainꎬ Morton
(1993) reported 2n= 42 (x = 7) for I􀆰 ramosissimus
(Hook. f.) Coddꎬ indicating it to be hexaploid. Lat ̄
erꎬ chromosome numbers of seven species and six
varieties of Isodon occurring in Japan were studied
by Yamashiro et al. (2005) and all of the taxa had
2n= 24 chromosomes.
Although most of the taxa of Isodon are distribu ̄
ted in Chinaꎬ only four species and two varieties
have had their chromosome numbers reported so
far (Table 1). Jin and Sha (2004) and Zhao et al.
Table 1  Data of chromosome numbers available for Isodon taxa before present study
Taxon Chromosomenumber (2n) Reference Origin
I􀆰 effusus (Maxim.) H. Hara 24 Yamashiro et al.ꎬ 2005 Japan
I􀆰 excisus (Maxim.) Kudô 24 Sokolovskaya et al.ꎬ 1986 Russia
I􀆰 inflexus (Thunb.) Kudô 24 Yamashiro et al.ꎬ 2005 Japan
I􀆰 japonicus (Burm. f.) H. Hara 24 Sokolovskaya et al.ꎬ 1986 Russia
I􀆰 japonicus (Burm. f.) H. Hara 24 Suzukaꎬ 1950ꎻ Yamashiro et al.ꎬ 2005 Japan
  var. glaucocalyx (Maxim.) H􀆰 W. Li 24 Jin and Shaꎬ 2004 China
I􀆰 longitubus (Miq.) Kudô 24 Yamashiro et al.ꎬ 2005 Japan
I􀆰 lophanthoides (Buch.  ̄Ham. ex D. Don) H. Hara 36 Huangꎬ 2011 China
  var. gerardianus (Benth.) H. Hara 24 Huangꎬ 2011ꎻ Zhang et al.ꎬ 2012 China
  var. graciliflorus (Benth.) H. Hara 24 Huangꎬ 2011ꎻ Zhang et al.ꎬ 2012 China
I􀆰 ramosissimus (Hook. f.) Codd 42 Mortonꎬ 1993 Cameroon
I􀆰 rubescens (Hemsl.) H. Hara 24 Zhao et al.ꎬ 2007 China
I􀆰 serra (Maxim.) Kudô 24 Huangꎬ 2011 China
I􀆰 shikokianus (Makino) H. Hara 24 Yamashiro et al.ꎬ 2005 Japan
  var. intermedius (Kudô) Murata 24 Yamashiro et al.ꎬ 2005 Japan
  var. occidentalis Murata 24 Yamashiro et al.ꎬ 2005 Japan
I􀆰 tricocarpus (Maxim.) Kudô 24 Yamashiro et al.ꎬ 2005 Japan
I􀆰 umbrosus (Maxim.) H. Hara 24 Yamashiro et al.ꎬ 2005 Japan
  var. excisinflexus (Nakai) K. Asano 24 Yamashiro et al.ꎬ 2005 Japan
  var. hakusanensis (Nakai) K. Asano 24 Wakabayashiꎬ 1973ꎻ Yamashiro et al.ꎬ 2005 Japan
  var. latifolius Okuyama 24 Yamashiro et al.ꎬ 2005 Japan
  var. leucanthus (Murata) K. Asano 24 Yamashiro et al.ꎬ 2005 Japan
265                                  植 物 分 类 与 资 源 学 报                            第 36卷
(2007) identified 2n = 24 for I􀆰 japonicus var. glau ̄
cocalyx (Maxim.) H􀆰 W. Li and I􀆰 rubescens (Hemsl.)
H. Haraꎬ respectively. Most recentlyꎬ Huang (2011)
checked the chromosomes of two species and two va ̄
rieties of the genus and reported 2n = 24 for I􀆰 serra
(Maxim.) Kudôꎬ I􀆰 lophanthoides (Buch.  ̄Ham. ex
D. Don) H. Hara var. gerardianus (Benth.) H. Ha ̄
raꎬ and I􀆰 lophanthoides var. graciliflorus (Benth.)
H. Haraꎬ but 2n = 36 for I􀆰 lophanthoides var. loph ̄
anthoidesꎬ which suggested this species to be trip ̄
loid. Identical chromosome numbers for I􀆰 lophantho ̄
ides var. gerardianus and I􀆰 lophanthoides var. gracil ̄
iflorus were further verified by Zhang et al. (2012).
The remaining taxa of the genusꎬ especially those
distributed in Southwestern Chinaꎬ have not yet been
investigated cytologically. Thusꎬ further studies to
obtain basic information are badly needed.
The main objective of present contribution is to
examine the chromosome numbers of several repre ̄
sentatives of Isodon from Chinaꎬ especially from the
region of Hengduan Mountains. We also hope to e ̄
valuate the systematic significance of chromosome
data for the genus. It forms a part of our research on
the taxonomy of Isodon ( Xiang and Liuꎬ 2012)ꎬ
and the cytological study of Lamiaceae from Eastern
Asia ( Funamoto and Ogawaꎬ 2004ꎻ Funamotoꎬ
2007ꎻ Funamoto et al.ꎬ 2008ꎬ 2009ꎻ Funamoto and
Smirnovꎬ 2011).
1  Materials and methods
Mericarps of 16 populations belonging to 13
taxa (11 species and two varieties) of Isodon were
collected from plants growing under natural condi ̄
tions in Gansuꎬ Sichuanꎬ Tibetꎬ and Yunnanꎬ Chi ̄
na. Voucher specimens were kept at Herbarium of
Kunming Institute of Botanyꎬ Chinese Academy of
Sciences ( KUN). Nomenclature of Isodon in this
study follows Li & Hedge (1994)ꎬ except for I􀆰 poly ̄
stachys (Y􀆰 Z. Sun) H. Hara which is here retained
as a distinct species whereas Li (1988) and Li &
Hedge (1994) reduced it as a synonym of I􀆰 coetsa
(Buch.  ̄Ham. ex D. Don) Kudô. Additionallyꎬ tax ̄
onomic treatment of I􀆰 lophanthoides var. gerardianus
follows the revision of Suddee et al. (2004)ꎬ in which
the variety was treated as a synonym of I􀆰 lophantho ̄
ides var. graciliflorus.
The mericarps were sown on wet filter paper in
petri ̄dishes for germination. Freshly growing root
tips were collected from the above materials for cyto ̄
logical investigations. They were cut off 5 - 10 mm
long and pretreated in 2 mmol􀅰L-1 8 ̄hydroxyquino ̄
line for 4 h at 20 ℃ꎬ and then fixed in 45% acetic
acid for 10 min at about 2 ℃ . Finally they were mac ̄
erated in a mixture of 45% acetic acid and 1 mol􀅰L-1
hydrochloric acid (1∶1) for 20-23 s at about 60 ℃ꎬ
and stained in 2% aceto ̄orcein for over 30 min at
room temperature in a moist chamber with 45% ace ̄
tic acid. Slide preparations were made using the con ̄
ventional aceto ̄orcein squash methods and were
faintly heated under an alcohol frame for 1-2 s be ̄
fore observation (Funamoto and Ogawaꎬ 2004). Pho ̄
tomicrographs were taken from freshly prepared slide
glasses using OLYMPUS Digital Camera ( DP72 ̄
SET ̄A ̄2) System.
For the determination of chromosome numbersꎬ
at least five individuals of each population were in ̄
vestigatedꎬ and for each individualꎬ chromosome
numbers of 5-10 cells were counted at somatic met ̄
aphase. Chromosomes at the resting state and mitotic
prophase were observed as well. Description of mor ̄
phological characteristics of the resting nuclei fol ̄
lowed the classification of Tanaka (1971).
2  Results and discussion
Chromosome numbers of the 13 taxa are listed
in Table 2 and morphology and size of the chromo ̄
somes are illustrated in Figs􀆰 1 - 2. All species and
varieties have the chromosome number 2n = 24ꎬ ex ̄
cept for I􀆰 coetsa (2n= 24ꎬ 48). Thusꎬ x= 12 can be
inferred as the basic chromosome number of Isodon
from China. The result largely corroborates that of
Yamashiro et al. ( 2005) who contributed to the
chromosome numbers of Isodon occurring in Japan.
In their studyꎬ all seven species and six varieties
3655期      XIANG Chun ̄Lei et al.: Cytology of Thirteen Taxa in the Genus Isodon (Lamiaceae: Nepetoideae) 􀆺     
from Japan have 2n = 24 chromosomes. Considering
that chromosomes of Isodon are of unclear centro ̄
meres and rather small sizes (generally smaller than
2 μmꎬ see Figs􀆰 1-2)ꎬ which is in agreement with
previous studies (Jin and Shaꎬ 2004ꎻ Yamashiro et
al.ꎬ 2005ꎻ Huangꎬ 2011ꎻ Zhang et al.ꎬ 2012)ꎬ de ̄
tailed karyotype analysis was not implemented suc ̄
cessfully in present study. According to the classifi ̄
cation of Tanaka (1971)ꎬ the resting nuclei of the
Isodon species studied belong to the rod prochromo ̄
some type. Rod ̄shaped heteropycnotic bodies with
varied size and shape can be observed. The surfaces
of the prochromosomes are smooth. A heterochromat ̄
ic segment located in the proximal region of the
chromosome forming by each prochromosome can be
observed as well.
For all taxa except I􀆰 lophanthoides var. gracili ̄
florusꎬ chromosome numbers have not been counted
beforeꎬ and our result (Table 2ꎻ Fig􀆰 1Hꎬ I) is con ̄
sistent with previous findings that I􀆰 lophanthoides
var. graciliflorus has 2n = 24 chromosomes (Huangꎬ
2011ꎻ Zhang et al.ꎬ 2012). Noticeablyꎬ the number
2n= 36 was reported by Huang (2011) from I􀆰 lop ̄
hanthodies var. lophanthoidesꎬ suggesting this taxa to
be triploid. The result can be confirmed by evidence
from the previous palynological survey of I􀆰 lophanth ̄
odies that most of its pollen grains were found to be
abortive tetrads with various shapes ( Chen et al.ꎬ
2000ꎻ Huangꎬ 2011)ꎬ and from our observation in
the wild that most of the mericarps of the species
Table 2  List of taxaꎬ collection dataꎬ and chromosome numbers of Isodon examined in this study
Taxon Chromosomenumber (2n)                         Collection data
I􀆰 albopilosus (C􀆰 Y. Wu & H􀆰 W. Li)
H. Hara 24
Chinaꎬ Gansuꎬ Kangxianꎬ Qujiagouꎬ N33°22′47″ꎬ E105°29′08″ꎬ Alt. 1 400 mꎬ
Fang W et al. FW11150
I􀆰 coetsa (Buch. ̄Ham. ex D􀆰 Don) Kudô 24 Chinaꎬ Yunnanꎬ Shangri ̄Laꎬ Edi tunnelꎬ Alt. 2 500 mꎬ Dong HJ et al. D630
24 Chinaꎬ Yunnanꎬ Songmingꎬ Aziyingꎬ Guodongꎬ N25°23′59″ꎬ E102°43′15″ꎬ Alt.2 200 mꎬ Xiang CL et al. 500
48 Chinaꎬ Yunnanꎬ Longlingꎬ transplanted in Kunming Botanical Gardenꎬ Alt. 1 800 mꎬXiang CL 1012 ̄02
I􀆰 flabelliformis (C􀆰 Y. Wu) H. Hara 24 Chinaꎬ Sichuanꎬ Kangdingꎬ Pengbuxiꎬ N29°46′58″ꎬ E101°31′06″ꎬ Alt. 3 300 mꎬFang W et al. FW11259
I􀆰 forrestii (Diels) Kudô 24 Chinaꎬ Yunnanꎬ Lijiangꎬ Yuhuꎬ Xuesongcunꎬ Alt. 2 850 mꎬ Dong HJ et al. D452
I􀆰 gesneroides (J. Sinclair) H. Hara 24 Chinaꎬ Sichuanꎬ Xiangchengꎬ Ma ̄an ̄shanꎬ N 28°57′56″ꎬ E99°45′29″ꎬ Alt. 3 710 mꎬFang W et al. FW11277
I􀆰 lophanthoides var. graciliflorus
(Benth.) H. Hara 24
Chinaꎬ Yunnanꎬ Songmingꎬ Aziyingꎬ Guodongꎬ N25°23′59″ꎬ E102°43′15″ꎬ Alt.
2 200 mꎬ Xiang CL et al. 507
I􀆰 oreophilus var. elongatus (Hand. ̄
Mazz.) A􀆰 J. Paton & Ryding 24
Chinaꎬ Sichuanꎬ Muliꎬ the way from Muli to Badiaoꎬ N27°58′33″ꎬ E101°16′35″ꎬ
Alt. 2 850 mꎬ Fang W et al. FW11088
I􀆰 parvifolius (Batalin) H. Hara 24 Chinaꎬ Gansuꎬ Zhouquꎬ Lijieꎬ N33°53′31″ꎬ E104°03′11″ꎬ Alt. 1 567 mꎬ FangW et al. FW11184
I􀆰 pleiophyllus (Diels) Kudô 24 Chinaꎬ Yunnanꎬ Lijiangꎬ Yuhuꎬ Xuesongcunꎬ Alt. 2 850 mꎬ Dong HJ et al. D467
I􀆰 polystachys (Y􀆰 Z. Sun) H. Hara 24 Chinaꎬ Yunnanꎬ Songmingꎬ Aziyingꎬ Guodongꎬ N25°23′59″ꎬ E102°43′15″ꎬ Alt.2 200 mꎬ Xiang CL et al. 510
I􀆰 racemosus (Hemsl.) Murata 24 Chinaꎬ Gansuꎬ Kangxianꎬ Jia’anꎬ Qinghe foresty stationꎬ N33°14′27″ꎬ E105°49′05″ꎬ Alt. 1 596 mꎬ Fang W et al. FW11174
I􀆰 scoparius ( C􀆰 Y. Wu & H􀆰 W. Li)
H. Hara 24
Chinaꎬ Yunnanꎬ Lijiangꎬ Hutiaoxiaꎬ N27°20′03″ꎬ E100°12′21″ꎬ Alt. 2 550 mꎬ
Dong HJ et al. D571
I􀆰 weisiensis (C􀆰 Y. Wu) H. Hara 24 Chinaꎬ Yunnanꎬ Deqinꎬ Benzilanꎬ Mt. Baimaꎬ Alt. 3 050 mꎬ Dong HJ et al. D623
24 Chinaꎬ Yunnanꎬ Deqinꎬ Shenpingꎬ N29°26′40″ꎬ E98°57′03″ꎬ Alt. 3 482 mꎬ LiuED et al. 3343
465                                  植 物 分 类 与 资 源 学 报                            第 36卷
were also abortive. On one handꎬ triploidy is always
thought to be a hindrance to the origin of fertile spe ̄
cies due to the high order of meiotic irregularity
which it brings about (Storeyꎬ 1950). On the other
handꎬ I􀆰 lophanthodiesꎬ distributed in wet hillsꎬ for ̄
ests and ravines in Southern Chinaꎬ is one of the
most widespread species of Isodon. It can also be
found in Indiaꎬ Myanmarꎬ Nepalꎬ Thailandꎬ and
Vietnam (Li and Hedgeꎬ 1994). Thusꎬ it is worthy
to further elucidate the reproduction mechanism of
I􀆰 lophanthodies based on a multidisciplinary investi ̄
gation.
The monotypic genus Skapanthus C􀆰 Y. Wu &
H􀆰 W. Li was delimited by Li (1975) and Wu and
Li ( 1977) to accommodate the species previously
known as Plectranthus oreophilus Dielsꎬ as it was
readily differentiated from Plectranthus by several
morphological characters. Laterꎬ the genus was trea ̄
ted as a synonym of Isodon by Paton and Ryding
(1998). Hereꎬ we counted the chromosome number
Fig􀆰 1  Photomicrographs of somatic chromosomes at metaphase in Isodon taxa from China
A. I􀆰 albopilosusꎻ B. I􀆰 coetsa (Dong HJ et al. D630)ꎻ C. I􀆰 coetsa (Xiang CL et al. 500)ꎻ D. I􀆰 coetsa (Xiang CL et al. 1012 ̄02)ꎻ
E. I􀆰 flabelliformisꎻ F. I􀆰 forrestiiꎻ G. I􀆰 gesneroidesꎻ Hꎬ I. I􀆰 lophanthoides var. graciliflorus. Scale bars= 5 μm
5655期      XIANG Chun ̄Lei et al.: Cytology of Thirteen Taxa in the Genus Isodon (Lamiaceae: Nepetoideae) 􀆺     
Fig􀆰 2  Photomicrographs of somatic chromosomes at metaphase in Isodon taxa from China
Aꎬ B. I􀆰 oreophilus var. elongatusꎻ C. I􀆰 parvifoliusꎻ D. I􀆰 pleiophyllusꎻ E. I􀆰 polystachysꎻ F. I􀆰 racemosusꎻ G. I􀆰 scopariusꎻ
H. I􀆰 weisiensis (Dong HJ et al. D571) ꎻ I. I􀆰 weisiensis (Liu ED et al. 3343) . Scale bars= 5 μm
of I􀆰 oreophilus (Diels) A􀆰 J. Paton & Ryding var.
elongatus ( Hand.  ̄Mazz.) A􀆰 J. Paton & Ryding
and the result provides additional evidence for its ac ̄
commodation in Isodon. Like most Isodon speciesꎬ
I􀆰 oreophilus var. elongatus has 2n = 24 chromosomes
(Table 2ꎻ Fig􀆰 2Aꎬ B). In additionꎬ the treatment
is also supported by recent molecular phylogenetic
study that species of Isodon and Skapanthus formed a
group with strong support values in all analyses
(Zhong et al.ꎬ 2010).
Chromosomes numbers of three populations of
I􀆰 coetsa from Yunnan province were investigated.
The chromosome number of 2n = 24 from Shangri ̄La
(Table 2ꎻ Fig􀆰 1B) and Songming (Table 2ꎻ Fig􀆰 1C)
is half of that of the cytotype 2n = 48 from Longling
(Table 2ꎻ Fig􀆰 1D). The chromosome number 2n =
48 in the genus is also reported here for the first
time. With the assumed basic number of x = 12 for
Isodonꎬ both diploidy and tetraploidy exist within in ̄
dividuals of I􀆰 coetsa. The formation of the polyploidy
665                                  植 物 分 类 与 资 源 学 报                            第 36卷
of the species needs further investigation.
Due to the low frequency of polyploid chromo ̄
some numbers occurring in Isodon taxa studied to
dateꎬ it can be inferred that polyploid speciation may
not play an important role in the evolutionary history
of the genus as other author considered ( Zhong et
al.ꎬ 2010). It is more likely that their diversification
emerges at the diploid level (Yamashiro et al.ꎬ 2005).
Howeverꎬ studies of a larger number of species more
fully representing the well ̄recognized taxonomic groups
and of additional interspecific hybrid material would
probably contribute to the determination of origins
and relationships within Isodon. Furthermoreꎬ cyto ̄
logical knowledge may also be used in conjunction
with data from various sources to achieve a better
understanding of phylogenetic relationship and speci ̄
ation of Isodon taxaꎬ and consequently to reveal their
natural classification. Thusꎬ further studies are still
needed to fill the gap of our knowledge of Isodon.
Acknowledgements: The authors are grateful to Dr. En ̄De Liu
(KUN)ꎬ Mr. Wei Fangꎬ Dr. Hong ̄Jin Dongꎬ and Dr. Ze ̄Huan
Wang for their help in field survey and sample collection.
References:
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865                                  植 物 分 类 与 资 源 学 报                            第 36卷