全 文 ：秋枫属的染色体数目及其进化意义?
薛恒钢 , 周颂东 , 王 强 , 何兴金?? , 余 岩
( 四川大学生命科学院 , 四川 成都 610064)
摘要 : 对秋枫属两个种 Bischofia javanica和 B. polycarpa 的体细胞进行了染色体计数研究。结果表明这两个
种在形态学上虽然存在差异 , 如秋枫是圆椎花序 , 重阳木是总状花序 , 但染色体数目均为 2n= 196。同时 ,
结合细胞学、形态学和生态学特点探讨了秋枫属的染色体基数 , 多倍化的起源及其演化意义。
关键词 : 秋枫属 ; 染色体 ; 形态学 ; 大戟科
中图分类号 : Q 942 文献标识码 : A 文章编号 : 0253 - 2700 (2007) 02 - 193 - 05
Chromosome Number of Bischofia (Euphorbiaceae) and
Its Evolutionary Implications
XUE Heng-Gang, ZHOU Song-Dong, WANG Qiang, HE Xing-Jin* * , YU Yan
( College of LifeScience, Sichuan University, Chengdu 610064 , China)
Abstract: The chromosome numbers and morphology of B. javanica and B. polycarpa were studied . The chromosome
numbers of both species are2n= 196 . The inflorescence is panicled in B. javanica while racemes in B. polycarpa . Com-
bined with thecytological , morphological and ecological data, the basic number and the origin and evolution of polyploidy
of thegenus were discussed .
Key words: Bischofia; Chromosomes; Morphology; Euphorbiaceae
Bischofia Bl . is a genus consisting of only two
species distributed fromsouthern and southeastern Asia
to Australia and Polynesia in the Old World . They also
occur in southwestern, central , eastern, and southern
China ( Wu, 1991 ) . It was an isolated genus in the
Euphorbiaceae, without any morphologically similar
neighbors in the subfamily Phyllanthoideae ( Webster,
1975 , 1994) . Although Airy Shaw (1965 , 1967) sug-
gested a relationship with the Staphyleaceae, evidence
fromembryology ( Bhatnagar and Kapil , 1973 ) , wood
anatomy (Mennega, 1987) , and leaf anatomy (Levin,
1986 a, b ) supports retention in Euphorbiaceae . In the
systematic treatment of the Euphorbiaceae by Webster
( 1975 , 1994 ) Bischofia was placed in the tribe
Bischofieae of subfamily Phyllanthoideae . Most re-
cently, based on the molecular data, Wurdack et al .
(2004) included Bischofia as agenus of Phyllanthace-
ae which was segregated fromEuphorbiaceae sensu lato
by APG II ( 2003 ) .
Bischofia polycarpa has affinitieswith B. javanica
and is considered as northern ecotype of B. javanica
( Wurdack et al . 2004 ) . However, recent research
suggests its segregation from B. javanica ( Li , 1994;
Yang, 1998; Radcliffe-Smith, 2001 ) . B. javanica is
a wide-ranging, invasive evergreen or semi-evergreen
woody treewith amaximum height of 40 m and diame-
ter of 2 .3 mwhile B. polycarpa, is a popular decidu-
ous tree common in central Chinaoccurring in forests at
elevations less than 1 000 m . Thewood of both B. jav-
anica and B. polycarpa is red, heavy, hard, and fine
云 南 植 物 研 究 2007 , 29 (2) : 193～197
Acta Botanica Yunnanica

?
?? ?Author for correspondence; E-mail : xingjinhe@ yahoo. com. cn; Tel : + 86 - 28 - 85415006; Fax: + 86 - 28 - 85415006
Received date: 2006 - 09 - 27 , Accepted date: 2007 - 03 - 07
作者简介 : 薛恒钢 (1971 - ) 男 , 博士研究生 , 主要从事植物分类的研究。 ?
Foundation item: 国家自然科学基金 ( 30670146) , 科技部自然科技资源平台专项 ( No . 2005DKA21403) 资助
grained, making it useful material for building . The
fruits are used in winemaking . Containing 30 - 54 per-
cent oil , the edible seeds are used as asourceof lubri-
cant . The bark is a source of red dye . The roots are
usedmedicinally .
It is clear that the relationship of the two species
and theorigin and evolutionof thisgenushavenot been
completely elucidated . Webster (1994 ) noted that in-
florescence structure was an important systematic char-
acter in Euphorbiaceae . Hans ( 1973 ) , after studying
the chromosome of 123 speciesof Euphorbiaceae, con-
cluded that chromosomal knowledge could reveal some
unsuspected situations or endorse the existing opinion .
There is a scarcity of reports on chromosome studies
within Bischofia, probably due to the small size and
large number of their chromosomes (Mehra and Gill ,
1968; Mehra and Hans, 1969; Hans, 1973) . It was
therefore considered that a study of the morphology,
and especially theinflorescence structure, together with
data fromthe detailed study of the chromosomeof B. -
javanica and B. polycarpa could contribute towards an
understanding of their evolution .
Material and Methods
The origin of the specimens is given inTable1 , withan in-
dication of the voucher specimens which were deposited in the
Herbarium of the College of Life Science, Sichuan University
(SZ) , Chengdu, China . Mitotic studies were made on root tips
obtained from plants transplanted to the experimental garden of
Sichuan University .
Table 1 Collection sites in Chinaof the two Bischofia species studied
Plant Accession number and site
Bischofia javanica X 221010 ?: Abandoned farm at Sichuan University
Bl . L 221011 ?: Grassland E′meishan, Sichuan
X 221012 ?L : Roadside 5 km along railway,
J ingkouhe, Sichuan
B ?. polycarpa (Levl .) X 331010: Hilly country, Miyi , Sichuan
Airy Shaw X 331012 ?: Forest, Mabian, Sichuan
X 331014 ?: Brook bank, Wolong, Sichuan
X 331018 ?: Valley, Yanyuan, Sichuan
For mitotic studies, root tipswerecollected in themorning,
treated with 0 .002 mol?L 8-hydroxyquinoline ( Tijo and Levan,
1950) for 3 .5 - 4.5 hat roomtemperature, fixed in 3∶1 ethanol-
acetic acid ( L?ve and L?ve, 1975 ) for at least one day, and
stored in70 % ethanol at 4±2℃ . Then they weremacerated in
1 mol?L hydrochloric acid at 60℃ for about 5 minutesand subse-
quently stained and squashed in 1 % aceto-orcein . One to five
plants fromeach populationand several roots per plantwere stud-
ied . As many metaphase plates as possible were studied from
each root . Number and apparent size of chromosomes was ob-
served . For apparent size of chromosomes, the terminology of
Stebbins (1938) was followed .
Result
Morphology
The morphological features of the two species are
summarized in Table 2 . The two accessions of B. java-
nica studied had basically the same morphological fea-
tures . There were two to three denticles per centimeter
along the leaves′serrated margin . The accessions of
B. polycarpa varied mainly in the leaves′base, those
of X 331010 beingbroadly round in contrast to theoth-
er three accessions, in which the leaves base were
broadly heart-shaped .
Chromosome number
B. javanica had a chromosome count of 2n= 196
in all cells analyzed . A typical mitotic cell is shown in
Fig . 1 : 1 , 2 . The chromosomes of B. javanica ranged
in length between 1 .08μmand 2 .88μm . B. polycarpa
also had a chromosome count of 2n = 196 in all cells
analyzed ( Fig . 1 : 3 , 4) . Its chromosome length was
between 1 .01μmand 2 .57μm .
Discussion
Basic chromosome number
The basic chromosomenumber for Bischofia rema-
ins controversial . Some authors ( Hans, 1973; Li ,
1994) considered the basic number for Bischofia to be
x = 7 . However, when the phylogenetic and morpho-
logical factor of the Bischofia were taken into account,
Wurdack ( 2004 ) considered x= 14 as basic number in
thegenus . Combined with the factors of ecological and
historical , the present study, based on all of the two
species of Bischofia, agreed to consider x = 14 as basic
number in thegenus .
Firstly, according to Stebbins ( 1971 ) , there are
differences in chromosome number between woody and
herbaceous angiosperms . Trees and shrubs have higher
basic numbers and, on the average, lower frequencies
of polyploidy within a genus than perennial herbs .
Woody plants of tropical regions resemble thoseof tem-
perate zones in the rarity of polyploidy series within a
genus, and their basic numbers were similar, with
modes at x= 11 , 12 , 13 and14 .Basic numbersof mod-
ern woody genera were derived by ancient polyploidy,
and that the original basic numbers of angiosperms,
491 云 南 植 物 研 究 29 卷
Table 2 Summary of the morphological characteristics of the accessions of the two species of Bischofia
Species Vegetative characteristics Floral characteristics Inflorescence
Bischofia javanica Bl .
X 221010 ?Evergreen woody tree, 40 mhigh and diameter of 0 .5 m . Small axillary flowers wereborne on dioe- Panicles
Leaves were trifoliatewith petiole 8 ?- 20 cm in length . cious panicles . The male inflorescencewas
Each papery leaflet was elliptic, 7 ?- 15 cm long and 4 - 8 *- 13 cm long and pubescent to glabrous,
8 ?cmwide, acute or caudate-acuminate apically and while the female inflorescence was 15 - 17
broadly cuneate to obtuse at base, with two to three cm long and pendant .
denticles per centimeter along the serrated margin .
L 221011 ?As X 221010 above . As X 221010 above . As X 221010 above .
X 221012 ?As X 221010 above . As X 221010 above . As X 221010 above .
B ?. polycarpa ( Levl .) Airy Shaw
X 331010 ?Deciduous- leavedwoody tree, 15 m high and diameter Small axillary flowers wereborne on dioe- Racemes
of 0 q. 3 m . Leaves were trifoliatewith petiole 9 - 13 ?. 5 cious racemes . Themale inflorescencewas
cm in length . Each papery leaflet was elliptic-ovate, 8 *- 13 cm long and pubescent to glabrous,
5 ?- 9 cm long and 3- 6 cmwide, acute acuminate apically while the female inflorescence was 2 e- 12
and, and broadly heart-shaped at base, with four to cm long and pendant .
five denticles per centimeter along the serrated margin .
X 331012 ?As X 331010 above . As X 331010 above . As X 331010 above .
X 331014 ?Leaves broadly round at base . All other characteristics As X 331010 above . As X 331010 above .
As X 331010 ?above .
X 331018 ?As X 331010 above . As X 331010 above . As X 331010 above .
Fig . 1 Photomicrograph of chromosome 1 , 2 . Bischofia javanica; 3 , 4 . Bischofia polycarpa .
5912 期 XU Heng-Gang et al .: Chromosome Number of Bischofia (Euphorbiaceae) and Its . . .
both woody and herbaceous, were x = 6 and x = 7 .
Both B. javanica and B. polycarpa are typical woody
angiosperms, B. polycarpa is primarily temperate zone
distributions, and B. javanica is tropical and temper-
ate, their basic number might be withmodes at x= 11 ,
12 , 13 and 14 . Furthermore Webster & Ellis ( 1962)
and Mangenot & Mangenot ( 1958) found x = 13 in the
subtribe Phyllanthinae, but the latter authors consid-
ered the basic number x = 12 to be primary within the
subtribe . Bischofica was atribeof thesubfamily Phyll-
anthoideae ( Webster 1975 , 1994 ) ; its basic number
might be near x= 13 or x = 12 .
Secondly, therewere no Bischofia taxa with 2n=
14 , andx = 7 cannot be taken as the basic chromosome
number so that x = 14 must be considered . However,
data fromthepresent paper showthat x = 14 could be a
derived basic number from x = 7 , this probably being
the most primitive basic number, now extinct . Wur-
dack et al . (2004) confirmed this assumption and sug-
gested that x = 14 could originate from x = 7 by
polyploidy .
Polyploidy
The ploidy level of both species of Bischofia was
14x ( x = 14 ) . This makes Bischofia different from
most of thewoody genus .
The frequency of polyploidy series in temperate as
well as tropical woody genera was low, a fact already
stated by Stebbins ( 1971) . This may be explained by
more consistent with the ecological relationships of
polyploids . Throughout the Tertiary period, and in the
case of tropical woody genera for perhaps even a longer
period of time, these groups did not have to cope with
drastic environmental differences . As components of
climax stages of plant succession, they had advanced
into new regions only when both climatic and soil con-
ditions had become similar to those in their previous
homes . Consequently, if occasional polyploid individu-
als had arose, they had not found any habitat in which
they had an adaptive superiority over their diploid pro-
genitors (Stebbins, 1971) . However, if drastic envir-
onmental changes followed by the opening up of new
habitats occurred, polyploids could establish and suc-
ceed . This was supported by the ecological position of
the exceptional woody generawhich do had ahigh per-
centageof polyploids . Throughout the glaciated regions
of the northern hemisphere, woody angiosperms that
had been most conspicuously successful as invaders of
newly available habitats had been the willows ( Salix)
and birches ( Betula) . These genera both have high
percentages of polyploidy (50% for Salix and 42% for
Batula) , and by far the greatest concentration of
polyploidy species and races was in the glaciated re-
gions (Stebbins, 1971) .
Some authors (Wu, 1991 , Wurdack et al . 2004)
demonstrated an incidence of invasive in B. javanica,
confirmed in this study, which demonstrates that many
B. javanica seedlings could easily be found in newly
available habitats which had been recently opened up
by human activity, such as old fields and roadsides .
This ecological position of Bischofia supported Steb-
bins′theory .
Evolution
In view of its chromosomes features, the genus is
a distinctive evolutionary lineage . Stebbins ( 1950 )
stressed the relationships between polyploidy and radi-
cal disturbances of thehabitat and added later (1971)
that these ancient cycles of polyploidy among woody
plants were promoted by radical disturbances of the
habitat and the occupation of newly available habitats .
The most probable general hypothesis, therefore, was
that the polyploidy which gave rise to thebasic numbers
of woody plants took place at various times during the
Cretaceous and the earliest part of the Tertiary period,
whilethe diversification of species on the basis of sec-
ondary basic numbers was largely a product of the Ter-
tiary and Quaternary periods (Stebbins, 1971) . Bischo-
fia with high chromosome numbers, with no close rela-
tives and restricted distribution seemto represent the fi-
nal stageof maturity of polyploidy complex, the“relic-
tual polyploids”, the term coined by Stebbins (1971) .
The polyploidy probably was an old event, various au-
thors (Awasthi , 1989; Yang, 1998) had identified old-
est fossil B. javanica fromwithin different Eocenesedi-
ments ( 53 - 33.7 myr) , then its low ploidy members
were likely to become progressively more restricted in
geographic distribution and finally extinct or those
which evolve adaptive combinations and chromosome
structures which were so radically different from those
possessed by the ancestors of the polyploids that they
place these newly evolved low ploidy populations be-
yond the recognizable limitsof the polyploidy complex .
Bischofia Bl . contains only two species: B. java-
nica and B. polycarpa . Indeed, morphologically B. jav-
691 云 南 植 物 研 究 29 卷
anica distinct from B. polycarpa in having panicled in-
florescence than racemes . Ecologically, B. javanica is a
wide-ranging, invasive evergreen or semi-evergreen
woody tree, whereas, B. polycarpa is apopular decidu-
ous tree common in central Chinaoccurring in forests at
elevations less than 1 000 m . It is well known that floral
features aremore reliablefor taxonomic and phylogenetic
classification than other types of morphological features
(Heywood, 1976) . According to Stebbins (1950) , the
reproductive organs of modern seed plants, which are
simpler in structure and development, are many times
less likely to be primitively simple than theywere to be
reduced and simplified from organs which were both
structurally and ontogenetically more complex in the
phylogenic ancestorsof themodern form .The panicle is
an indicationof primitiveness and the reductionof floral
parts is an indication of evolutionary advancement . The
dataon the inflorescence therefore suggest that B. jav-
anica is more primitive than B. polycarpa . However,
the chromosome numbers of both species were 2n =
196 , the really role of karyotype in the evolution of
B. javanica and B. polycarpa is obscure .
Since the cytotaxonmy has not been studied in
sufficient detail due to the small size and largenumber
of their chromosomes, any evaluation based on karyo-
type of the phylogenetic trends recognizes within
Bischofia would be premature . Analyses including
more data, such as molecular features and pollination
biologically, are necessary to clarify the phylogenetic
and taxonomic status of the two species .
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