全 文 ：Floral Ontogeny in Itea yunnanensis (Iteaceae)
GE Li_Ping1 ,2 , LU An_Ming1＊ , PAN Kai_Yu1
(1.Laboratory of Systematic and Evolutionary Botany , Institute of Botany , The Chinese Academy of Sciences , Beijing 100093 , China;
2.College of Forestry , Shanxi Agricultural University , Taigu 030801, Shanxi , China)
Abstract: To provide evidence insight into the phylogenetic position of Itea L., we observed floral ontogeny
of Itea yunnanensis Franch.under the scanning electron microscope(SEM)for the first time.The floral phyl-
lotaxis is whorled and floral organogenesis follows centripetal pattern.Sepal initiation is in a two_fifths helical
order.Petal initiation appears simultaneous , and petals grow at an ordinary rate.The haplostemony of this
species arises slightly later than petals but earlier than gynoecium in initiation.Two carpels are free at the early
stage of floral ontogeny , but incurve , get closer and become appressed to each other later.Paraffin transverse
sections series of gynoecium at anthesis show that two carpels are connate on the ventral side through their en-
tire length.At last , two carpels within the ovary fuse completely , forming two locules separated by a septum ,
the ventral vascular bundles in two stylar lobes are connected through the parenchyma , and the stigma lobes
become fused.These observations are different from those by Bensel and Palser (1975).The gynoecia they
describedmight be not mature , but rather at early developmental stage.We compared floral developmental pat-
tern and floral structure of Itea with its related taxa.In I .yunnanensis petals grow in the way that is different
from that of some related taxa such as Saxifragaceae sensu stricto , Hydrangeaceae , Ribes , Brexia.The devel-
oping pattern of gynoecium in I .yunnanensis is similar to that of some members in the Saxifragaceae sensu
stricto and Hydrangeaceae.The treatment to raise taxonomic rank of Itea from genus to family , Iteaceae , is
supported by our results.
Key words: Itea yunnanensis;floral ontogeny
The genus Itea L.consisting of about 18 species ,
mainly occurs in eastern Asia (from the Himalayas to
Japan)and Malaysia , with only one species(Itea virgini-
ca)disjunctly extending to eastern North America.There
are about 15 species in China , where ten are endemic(Jin and Ohba , 2001).
The genus Itea is often treated as the only member
of the subfamily Iteoideae under the Saxifragaceae sensu
lato(Saxifragaceae s.l.)(Niu and Ohba , 1999).But
the Saxifragaceae s.l.has been proved to be a typically
polyphyletic assemblage by new pieces of evidence , and
the distinct families ranging from 3 to 15 were recognized
in this lineage by different authors (Morgan and Soltis ,
1993;Soltis and Soltis , 1997).Among all these treat-
ments , the position of Itea is particularly controversial(Morgan and Soltis , 1993;Soltis and Soltis , 1997).
Based on different lines of evidence , such as morphologi-
cal , embryological , cytological , palynological , molecu-
lar , the alliances of Itea proposed by different authors are
respectively the Saxifragaceae sensu stricto (Saxifragaceae
s.s.), Ribes (included in the Grossulariaceae),
Pterostemon (Pterostemonaceae , Mexico), Escallonia ,
Choristylis and Brexia (Bensel and Palser , 1975;Morgan
and Soltis , 1993;Soltis and Soltis , 1997).
Floral ontogeny has been shown to be valuable in
elucidating phylogenetic position for generic and supra_
generic taxa(Tucker , 1992;Liang et al , 1996;Roels et
al , 1997;Feng and Lu , 1998;Sun et al , 1998;Huf-
ford , 2001).However , the floral organogenesis in Itea
has not been reported yet so far.The present work aims to
provide evidence of floral ontogeny in Itea for further
study on its phylogeny.
1 Materials and Methods
Inflorescences and flower buds of Itea yunnanensis
Franch.at different developmental stages were collected
from Kunming Botanical Garden in Yunnan Province , Chi-
na , April 2001.The voucher specimen , LU An_Ming
2082 , is deposited in the Herbarium , Institute of Botany ,
The Chinese Academy of Sciences (PE).The materials
were fixed in fixative FAA(5 parts formalin∶6 parts acetic
acid∶89 parts 50% alcohol).Just before dissection , the
flower buds were transferred to 95% alcohol through a se-
ries of concentrations of alcohol.Bracts and larger floral
organs were removed from each piece under a dissection
microscope.Appropriate dissection was followed by further
dehydration through an alcohol_isoamyl acetate series and
critical point drying with CO2.The materials were then
mounted on aluminum stubs and coated with gold_palladi-
um before they were observed under the Hitachi S_800
scanning electron microscope (SEM).The micrographs
were taken under the SEM.Flower buds for histological
study were dehydrated in an alcohol series , embedded in
paraffin , sectioned at a thickness of 10 μm with a rotary
microtome.The preparations were stained with safranin and
fast green for light microscopy observations.
Received:2002-06-12 Accepted:2002-09-18
Supported by the National Natural Science Foundation of China(30130030)and by a grant of Systematic and Evolutionary Biology , The Chinese Academy of Sci-
ences(219222F).
＊Author for correspondence.E_mail:
植 物 学 报
Acta Botanica Sinica 2002 , 44 (11):1261-1267
1262 植物学报 Acta Botanica Sinica Vol.44 No.11 2002
2 Results
2.1 Organography
The bisexual and regular flowers are small , numer-
ous , often in a fascicle of three flowers , and arranged he-
lically into a terminal raceme_like inflorescence(Fig.1).
The central and larger one of three fascicle flowers has one
bract , while each of the lateral two has one bract and two(or one)bracteoles (Figs.2 , 3 , 19).The bracts are
small and subulate.The flowers have five triangular_
lanceolate sepals;five white or yellowish green , linear_
lanceolate , valvate petals , which are erect , slightly in-
curved distally at anthesis.Five stamens are inserted at
the margin of disc (Figs.25 ,26), alternate with petals.
The anthers are oblong , dorsifixed (Fig.25), introrse
and tetrasporangiate (Fig.26);the distal connective is
slightly protrusive.The gynoecium is of two united
carpels;ovary is three_quarters inferior (Fig.28), 2_
locular and with numerous ovules borne on an axile pla-
centa;disc is ringlike , thick , on the top of ovary (Fig.
26);the major part of ovary wall is adnate to floral cup(Fig.28).The gynoecium has a single , 2_grooved style(Fig.26), and a capitate stigma (Fig.29).
2.2 Sepal initiation and development
A number of floral primordia are arranged helically
at the upper part of an inflorescence axis and initiated in
acropetal order(Fig.1).The floral apex is dome_like at
first , but it is not still convex after sepal primordia initia-
tion(Figs.2 , 3).Sepals are initiated successively on the
periphery of the floral apical meristem in a two_fifths helix(Fig.4).The abaxial and nonmedian sepal arises first(Figs.3 , 4), followed by the adaxial sepal , with the
third in a lateral_abaxial position , and the fourth and fifth
in lateral_adaxial positions (Fig.4).Subsequently , the
sepal primordia enlarge and grow into triangular form.The
sepals are half as long as petals at anthesis.
2.3 Petal initiation and development
During the sepal growth five petal primordia are ini-
tiated nearly simultaneously in positions centripetal to the
sepals and alternating with them(Figs.5 , 6).The petal
primordia begin to dorsiventrally flatten , broaden and un-
dergo marginal growth(Fig.12).All incipient petals be-
come inwardly tilted toward the center of the floral apex
and appear to be square_like (Fig.15), but later they
elongate , incurve apically and become hooked(Figs.17 ,
21).Petals are valvate , and they are longer than sepals
after anthers have formed.
2.4 Stamen initiation and development
When the petal primordia begin to grow , five stamen
primordia are initiated almost simultaneously inside petals
and in antesepalous positions (Figs.7 , 8).Because of
rapid growth , they are nearly as large as petal primordia
in size at the early developmental stage.At this time ,
visible are ten subequal size round primordia(Fig.9), of
which the outer five are petal primordia , and the inner
antesepalous five are stamen primordia (Figs.9 , 10).
Differentiation of the stamen primordia begins with dor-
siventrally flattening and distal expansion for anther for-
mation.Subsequently , anther region grows both radially
and tangentially , thecae and connective are formed , and
each anther at this time appears to be triangular from dor-
sal view , but hooked at apex;filaments are extremely
short(Figs.17 , 18 , 20).Then , median ventral grooves
forms first in the anthers (Fig.18), followed by lateral
grooves that delimit the microsporangia (Figs.21 , 22 ,
23).At this stage the anthers are oblate , with the hooked
and obtuse connective protrusion (Fig.23).The anthers
in larger buds are ellipsoid_ovoid (Fig.25).At anthesis
each theca opens by a longitudinal slit to release pollen
grains.
2.5 Gynoecium initiation and development
After stamen primordia initiation , the floral apex be-
come concave at the center , and a pentagon meristem
arises(Fig.9).As the depression deepen progressively ,
two free carpel primordia are formed on the torus (Figs.
11 , 13).They grow more rapidly on the dorsal side than
on the ventral one , and as a result each carpel primordi-
um appears to be horseshoe_shaped (Fig.14).Each in-
cipient carpel elongate upwards and become slightly thin
at the upper part , and then differentiate into a stylar
lobe , a stigma lobe as well as a part of the ovary.The
lower part of each carpel extends downwards and inserts
into the floral cup , developing into the major part of the
ovary(Figs.26 , 28).Two carpels are free from each oth-
er at the early stage of gynoecium development(Figs.14 ,
16 , 17);the subsequent development makes them ap-
proach at the ventral side and become appressed (Figs.
22 , 23 , 30 , 31).The distal tips of the carpels elongate
continuously upwards and become thinner , followed by
the formation of style and stigma (Figs.24 , 25).Cross
sections of the ovary at anthesis indicate that two carpels
fuse ventrally in a cup_shaped receptacle , with formation
→
Figs.1-17. Floral ontogeny in Itea yunnanensis(SEM micrographs).1.A young inflorescence with floral primordia and early floral buds ,×42.2.A young floral bud with one bract and two bracteoles , ×210.3.Sepal initiation , ×180.4.After sepals initiated , ×240.5.De-
veloping sepals and nearly simultaneously initiated petal primordia , ×150.6.After petals established , ×210.7.Showing the beginning of
androecium and progressive development of sepals and petals , ×180.8.Showing the nearly simultaneously initiated stamens , ×210.9.
Showing the stamen primordia(the inner five)and petal primordia(the outer five), ×300.10.The concave floral apex , ×150.11.The
center of a floral bud , showing the details of the floral apical ring meristem , ×300.12.A floral bud , the petals has already flattened , the
stamens begin to differentiate , ×120.13.Two carpels primordia arise on the torus , ×180.14.Two free , horse_shoes shape carpels ,
×300.15.Anther differentiation , ×132.16.A floral bud , showing the developing carpels.The visible part of the carpels remains indepen-
dent from each other , ×180.17.The petals are incurved apically.Anther and filament have formed on the incipient stamens , ×120.
Abbreviations:a , stamen(primordium);B , bract;b , bracteole;c , carpel;d , disc;F , floral apex;o , ovule;p , petal;s , sepal;s1-s5 ,
order of sepal initiation;st , stigma;stl , style.
GE Li_Ping et al:Floral Ontogeny in Itea yunnanensis(Iteaceae) 1263
1264 植物学报 Acta Botanica Sinica Vol.44 No.11 2002
of a septum between them(Figs.27 , 33).The ovary wall
is adnate to the cup_shaped torus.During the early carpel
development , two stylar lobes grow with different rates ,
and thus two lobes of stigma are not situated at the same
level(Figs.25 , 26), but the stylar lobes become the
same in length by anthesis.As shown in Fig.34 , the
ventral vascular bundles in two stylar lobes are united
through a line of narrow and long parenchyma , though the
margins of these two lobes remain free.Therefore , the
style at last appears as a single unit.Two lobes of the
stigma are also ventrally fused(Fig.35), forming a capi-
tate stigma with a furrow throughout the center(Fig.29).
3 Discussion
3.1 Initiation time and growth rate of petals
Table 1 lists the patterns of floral development of
Itea and its related taxa examined in the Saxifragaceae s.
l.It is suggested by Roels et al(1997), in the Saxifra-
gaceae s.s.and Ribes , that petal primordia are initiated
in a retarded manner:initiation is often simultaneous with
the antepetalous stamen primordia (Gelius , 1967), and
early petal growth is very limited.The petals do not follow
sepals in initiation but arise after sepals have been well
established , so the sepals cover the bud during the whole
Table 1 A comparison of patterns of floral development in Itea and its related taxa
Taxa
Order of
sepal
initiation
Developing
rate of petal
primordia
Stamen
No. Type
Gynoecium
No.of
carpel
Position of
ovary
Synstyly Pla
Itea yunnanensis 2/5 helix Normal 5 Hap 2 3/4 inf Cnt Ax
Choristylis 5 Hap 2 Inf Separate Ax
Ribes Successive Retarded 5(4) Hap 2 Inf Partially cnt Par
Saxifraga Successive Retarded 10 Obdip 2-5 Nearly sup-1/2
inf
Separate or cnt Ax
Astilbe aponica Successive 10 Obdip 2 Nearly sup Separate Ax
Rodgersia podophylla Successive Retarded 10 Obdip 2 Nearly sup Separate Ax
Chrysosplenium serre-
anum
Successive No petal 8 Obdip 2 1/2 inf Separate Par
Deutzia corymbosa 2/5 helix Fast 10 Dip 3 Inf Separate Ax
Philadelphus purpuras-
cens
2 by 2 Fast 25-33 Pol 4 1/2 inf Nearly cnt Ax
Kirengeshoma 2/5 helix Rapid 15 Pol 3-4 1/2 inf Separate Ax
Deinanthe Tight helix Fast Num Pol 5 1/2 inf Cnt Par
Hydrangea Tight helix Fast 10(8-25) Dip or pol 2-5 Partly inf_inf Separate or cnt
at the base
Escallonia Successive Normal 5 Hap 2-5 Inf Cnt Ax or par
Brexia Successive Rapid 5 Hap 5 Sup Cnt Ax
Pterostemon 10 Dip 5 Inf Partly cnt Ax
Ax , axile;Cnt , connate;Dip , diplostemonous;Hap , haplostemonous;Inf , inferior;Num , numerous;Obdip , obdiplostemonous;Par , parietal;Pla , placenta;
Pol , polyandrous;Sup , superior.
The data are from the references:Gelius , 1967;Hutchinson , 1967;Klopfer , 1973;Bensel and Palser , 1975;Jin et al , 1995;Takhtajan , 1997;Roels et al ,
1997;Hufford , 2001.
→
Figs.18-35. 18-29.Floral ontogeny in Itea yunnanensis(SEM micrographs).18.Showing five stamens and two carpels.The median
ventral grooves form in the anthers;note connective extend apically and appear hooked.Two carpels get closer each other, ×90.19.Outlook
of a floral bud , showing the base of pedicel with one bract and two bracteoles.At the stage , the sepals are longer than the petals , ×36.20.
The anthers appear triangular from dorsal view;the apical connective looks obtuse , ×48.21.The upper parts of two carpels meet together.
Lateral grooves arise in the anthers , ×66.22.Differentiating anther sacs and developing carpels , ×78.23.Four pollen sacs have formed.
Each distal connective looks like a small globe, ×60.24.Developing style , ×78.25.Showing the petals , stamens , style and stigma.Petal
is longer than any other floral organs at the stage.The petals appear hooked distally.The anthers are dorsifixed , ×24.26.A later floral bud ,
showing the disc, style and stigma , ×36.27.A transversal section through the ovary , indicating two locules , ovules borne on the axial pla-
centa , ×42.28.A lateral view of later gynoecium.The ovary wall has been partly removed to show 3/4 inferior ovary and numerous ovules ,
×42.29.A stigma at anthesis.Stigma look like a slightly 2_split capitate , its papillule cross each other along the middle region , ×78.30-35.Light microscopic sections through the gynoecium.30-32.Cross sections through an early gynoecium.30.Lower part of two carpels ,
×205.31.Middle part of two carpels , ×128.32.Upper part of two carpels , ×128.33-35.Paraffin cross sections through a mature gy-
noecium.33.Two carpels is fused within the ovary , ×32.3.34.Two stylar lobes are united through a line of narrow and long parenchyma ,
×64.5.35.The stigma is fused , ×64.5.
The abbreviations are the same as in Figs.1-17.
GE Li_Ping et al:Floral Ontogeny in Itea yunnanensis(Iteaceae) 1265
floral development(Roels et al , 1997).But in the Hy-
drangeaceae and Brexia , the plastochron between sepal
initiation and petal initiation is very short , and petal pri-
mordia grow rapidly .At a relatively early stage in ontoge-
ny , petals appear larger than sepals and cover the inner
parts of the bud(Roels et al , 1997).Our result , howev-
er , suggests that the perianth development of Itea is dif-
ferent from both of the above , but follow an intermediate
pattern.Petal primordia are initiated just after sepals es-
tablished(Fig.6), and develop in an ordinary rate , nei-
ther retarded nor accelerated.The sepals are not smaller
than the petals until the formation of tetrasporangium(Fig.21).Only after the stigma has been differentiated
do the petals become longer than the sepals.The sepals
cover the inner parts of the bud at the early stage of floral
development , while the petals cover the inner parts of the
bud at later development.Such a pattern is named as anOrdinary Type.
3.2 Type of androecium
As shown in Table 1 , Itea , Ribes , Choristylis , Es-
callonia and Brexia are haplostemonous , whereas most
members of the Saxifragaceae s.s.are obdiplostemonous(Klopfer , 1973).Diplostemony (often 8-10)is com-
mon in the Hydrangeaceae , while polyandry is also pre-
sent in Philadelphus , Kirengeshoma , Deinanthe , Platy-
crater.Pterostemon is also of diplostemony , but only the
outer five stamens are fertile (Hutchinson , 1967).
3.3 Attribute of gynoecium
Bensel and Palser (1975)described the gynoecium
of Itea yunnanensis as follows:a split appears between
the two carpels near the top of the ovary , at or below the
level where the floral cup becomes free from the ovary
wall , and the carpels are completely free from each other
from that level to the stigmas , but the stigmas are fused.
According to their observations , two carpels are f ree in
the entire stylar region in the species.However , our ob-
servations revealed a different development state from their
conclusion.Two carpels are free from each other at the
early stage of gynoecium development(Figs.14 , 16 , 17 ,
32), and then they incurve and get appressed gradually
with the further development.Their epidermis is not his-
tologically fused (Fig.31)until late stage of gynoecium
development , when the two carpels become connate
through the entire length , though the stylar region is unit-
ed only through a line of narrow and long parenchyma.
The free styles as described by Bensel and Palser (1975)
in Itea yunnanensis occurs only at the early stage of gy-
noecium development.In fact , two carpels gradually be-
come syncarpous and more or less fusion exists from ovary(through style)to stigma when the gynoecium is mature.
In the present systems of classification of an-
giosperms , Itea is placed in the Escalloniaceae(Hutchin-
sons Cunoniales , Thornes Hydrandeales)by Hutchin-
son(1973)and Thorne (1992), but in the Grossulari-
aceae under Rosales by Cronquist (1981).However ,
Dahlgren (1983) treated Itea as a separate family ,
Iteaceae , and placed it under Saxifragales.Takhtajans(Takhtajan , 1997)Iteaceae comprises two genera , Itea
and Choristylis , and the family is placed near Saxifr-
gaceae s.s.under Saxifragales.
The patterns of f loral ontogeny and the floral struc-
ture mentioned above indicate that the initiation and early
development of gynoecium in Itea are similar to those
found in the Saxifragaceae s.s.and some members in the
Hydrangeaceae , such as Hydrangea (especially the
species with two carpels , e.g.H.quercifolia), Deutzia ,
Philadelphus(Klopfer , 1973;Roels et al , 1997).How-
ever , petal development of Itea is different from that of
the Saxifragaceae s.s., the Hydrangeaceae , Ribes , and
Brexia.The type of androecium distinguishes Itea from
the Saxifragaceae s.s., the Hydrangeaceae and Pteroste-
mon.
Therefore , the genus Itea differs distinctly from all
presumedly related taxa , such as the Saxifragaceae s.s.,
the Hydrangeaceae , Brexia , Pterostemon and Ribes in
ontogeny.Our results support raising taxonomic rank of
Itea from a genus to a separate family , Iteaceae.But
confirmation of its systematic position and its natural rela-
tives need further comprehensive analyses based on more
data from fossil , anatomy , DNA sequence , etc.
Acknowledgements:The authors are grateful to Prof.
HONG De_Yuan , WANG Yin_Zheng and Dr.LIU Jian_
Quan for their valuable comments on the manuscript , Mr.
XIAO Yin_Hou as well as Ms.WEN Jie for their guide
during experiments and Mr.YANG Xue_Jian for develop-
ing photos.
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滇鼠刺花的形态发生(鼠刺科)
葛丽萍1 ,2 路安民1＊ 潘开玉1
(1.中国科学院植物研究所系统与进化植物学重点实验室 , 北京 100093;2.山西农业大学林学院 , 太谷 030801)
摘要: 在扫描电镜下 , 观察了滇鼠刺(Itea yunnanensis Franch.)花的形态发生。花 3 朵一束 , 排成总状花序。花器
官为轮状结构 ,向心发生;花萼以 2/5 螺旋式相继发生 , 5 个花瓣原基几乎同步地在花萼内侧与其互生的位置发生。
雄蕊单轮对萼 。当雄蕊发生后 ,花顶中心的分生组织开始凹陷 , 成为浅锅状;在其周围出现一个环状的分生组织 ,
随之 , 2心皮原基产生 , 进而发育为马蹄形。初期的心皮相互分离 , 随着进一步发育 , 心皮内卷 , 彼此靠近 、紧贴 , 逐
渐于腹面合生 ,形成 2 室的中轴胎座;花柱的腹维管束通过薄壁组织连通;花期柱头融合 , 因此该种为合生心皮。
对鼠刺属(Itea)及相关类群花发育性状和花结构进行了比较 ,支持把鼠刺属提升为鼠刺科(Iteaceae)的观点。
关键词: 滇鼠刺;花的形态发生
中图分类号:Q949 文献标识码:A 文章编号:0577-7496(2002)11-1261-07
收稿日期:2002-06-12 接收日期:2002-09-18
基金项目:国家自然科学基金(30130030);中国科学院生物分类区系学科发展特别支持费资助课题(219222F)。
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GE Li_Ping et al:Floral Ontogeny in Itea yunnanensis(Iteaceae) 1267