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 Life Science , 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 are 2n=196.The inflorescence is panicled in B.javanica while racemes in B.polycarpa.Com-
bined with the cytological , morphological and ecological data , the basic number and the origin and evolution of polyploidy
of the genus were discussed.
Key words:Bischofia;Chromosomes;Morphology;Euphorbiaceae
Bischofia Bl.is a genus consisting of only two
species distributed from southern 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).AlthoughAiry Shaw(1965 , 1967)sug-
gested a relationship with the Staphyleaceae , evidence
from embryology (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 a genus of Phyllanthace-
ae which was segregated from Euphorbiaceae sensu lato
by APG II(2003).
Bischofia polycarpa has affinities with 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 tree with a maximum height of 40m and diame-
ter of 2.3 m while B.polycarpa , is a popular decidu-
ous tree common in central China occurring in forests at
elevations less than 1 000m.The wood 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 a source of lubri-
cant.The bark is a source of red dye.The roots are
used medicinally.
It is clear that the relationship of the two species
and the origin and evolution of this genus have not 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 species of 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 the inflorescence structure , togetherwith
data from the detailed study of the chromosome of B.-
javanica and B.polycarpa could contribute towards an
understanding of their evolution.
Material and Methods
The origin of the specimens is given in Table 1 , with an 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 China of 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 221012L:Roadside 5 km along railway ,
Jingkouhe , 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 tips were collected in the morning ,
treated with 0.002 mol L 8-hydroxyquinoline (Tijo and Levan ,
1950)for 3.5-4.5 h at room temperature , fixed in 3∶1 ethanol-
acetic acid (Löve and Löve , 1975)for at least one day , and
stored in 70% ethanol at 4±2℃.Then they were macerated in
1 mol L hydrochloric acid at 60℃ for about 5 minutes and subse-
quently stained and squashed in 1% aceto-orcein.One to five
plants from each population and several roots per plant were 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 being broadly round in contrast to the oth-
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 1.08μm and 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 1.01μm and 2.57μm.
Discussion
Basic chromosome number
The basic chromosome number 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
the genus.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 the genus.
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 those of 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 and 14.Basic numbers of mod-
ern woody genera were derived by ancient polyploidy ,
and that the original basic numbers of angiosperms ,
194 云 南 植 物 研 究 29卷
Table 2 Summary of the morphological characteristi cs of the accessions of the two species of Bischofia
Species Vegetative characteristi cs Floral characteri stics Inf lorescence
Bischofia javanica Bl.
X 221010 Evergreen woody tree , 40m high and diameter of 0.5m. Small axi llary flowerswere borne on dioe- Panicles
Leaves were trifoliate with petiole 8-20 cm in length. cious panicles.The male inflorescence was
Each papery leaflet was elliptic , 7-15 cm long and 4- 8-13 cm long and pubescent to glabrous ,
8 cm wide , acute or caudate-acuminate apically and whi le the female inf lorescence 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-leaved woody tree , 15m high and diameter Small axi llary flowerswere borne on dioe- Racemes
of 0.3 m.Leaves were trifoliate with petiole 9-13.5 cious racemes.The male inflorescence was
cm in length.Each papery leaflet was elliptic-ovate , 8-13 cm long and pubescent to glabrous ,
5-9 cm long and 3-6 cm wide , acute acuminate apically whi le the female inf lorescence was 2-12
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.
1952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 with modes at x=11 ,
12 , 13 and 14.Furthermore Webster &Ellis(1962)
andMangenot &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 a tribe of the subfamily Phyll-
anthoideae (Webster 1975 , 1994);its basic number
might be near x=13 or x=12.
Secondly , there were no Bischofia taxa with 2n=
14 , and x=7 cannot be taken as the basic chromosome
number so that x =14 must be considered.However ,
data from the present paper show that 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 the woody 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 genera which do had a high per-
centage of 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 the habitat 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 the basic numbers
of woody plants took place at various times during the
Cretaceous and the earliest part of the Tertiary period ,
while the diversification of species on the basis of sec-
ondary basic numbers was largely a product of the Ter-
tiary andQuaternary periods(Stebbins , 1971).Bischo-
fia with high chromosome numbers , with no close rela-
tives and restricted distribution seem to represent the fi-
nal stage of 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 from within different Eocene sedi-
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 limits of the polyploidy complex.
Bischofia Bl.contains only two species:B.java-
nica and B.polycarpa.Indeed , morphologically B.jav-
196 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 a popular decidu-
ous tree common in central China occurring in forests at
elevations less than 1 000m.It is well known that floral
features are more reliable for 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 they were to be
reduced and simplified from organs which were both
structurally and ontogenetically more complex in the
phylogenic ancestors of the modern form.The panicle is
an indication of primitiveness and the reduction of floral
parts is an indication of evolutionary advancement.The
data on 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 large number
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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1972期 XU Heng-Gang et al.:Chromosome Number of Bischofia (Euphorbiaceae)and Its ...