ontogenia flori la fam. magnoliaceae

8/13/2019 Ontogenia flori la Fam. Magnoliaceae

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Comparative floral anatomy and ontogeny in Magnoliaceae

F. Xu1 and P. J. Rudall2

1South China Botanical Garden, Academia Sinica, Guangzhou, China2Royal Botanic Gardens, Kew, Richmond, Surrey, UK

Received November 16, 2004; accepted June 9, 2005

Published online: March 8, 2006

Springer-Verlag 2006

Abstract. Floral anatomy and ontogeny are de-

scribed in six species of Magnoliaceae, representing

the two subfamilies Liriodendroideae (Liriodendron

chinese and L. tulipifera) and Magnolioideae,

including species with terminal flowers (Magnolia

championi, M. delavayi, M. grandiflora, M. pae-

netalauma) and axillary flowers (Michelia crassipes).

The sequence of initiation of floral organs is from

proximal to distal. The three distinct outermost

organs are initiated in sequence, but ultimately form

a single whorl; thus their ontogeny is consistent with

a tepal interpretation. Tepals are initiated in whorls,

and the stamens and carpels are spirally arranged,

though the androecium shows some intermediacy

between a spiral and whorled arrangement. Carpels

are entirely free from each other both at primordial

stages and maturity. Ventral closure of the style

ranges from open in Magnolia species examined to

partially closed inMichelia crassipesand completely

closed inLiriodendron, resulting in a reduced stigma

surface. Thick-walled cells and tannins are present

in all species except Michelia crassipes. Oil cells are

normally present. Floral structure is relativelyhomogeneous in this family, although Liriodendron

differs from other Magnoliaceae in that the

carpels are entirely closed at maturity, resulting

in a relatively small stigma, in contrast to the

elongate stigma of most species of Magnolia. The

flower ofMagnoliadoes not terminate in an organ

or organ whorl but achieves determinacy by gradual

diminution.

Key words: Floral development, Floral morphology,

Liriodendron, Magnolia, Michelia.

Introduction

Magnoliaceae are a well-defined and horticul-

turally important family of about 230 species

of trees and shrubs characterised by large

flowers with numerous tepals and fertile partsinserted separately on an elongated axis. More

than 80% of species of Magnoliaceae are

distributed in subtropical and tropical regions

of eastern Asia; the remainder occur in Amer-

ica, indicating a relictual tropical disjunction

(Azuma et al. 2001). Renewed debate on the

systematics of the family has been stimulated

by several recent cladistic analyses, both

morphological (Li and Conran 2003) and

molecular (Shi et al. 2000), but several out-

standing questions remain.

Dandy (1927) proposed the first compre-hensive taxonomic treatment of Magnoliaceae,

which recognised ten genera distributed in two

tribes: Liriodendreae (sole genus Liriodendron)

and Magnolieae, including Magnolia, Mang-

lietia, Michelia, and six smaller genera. Sub-

sequent authors have proposed several

different infrafamilial taxonomic schemes, but

Pl. Syst. Evol. 258: 115 (2006)

DOI 10.1007/s00606-005-0361-1


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all of them divide the family into two

subfamilies, of which one, Liriodendroideae,

includes the sole genus Liriodendron, and the

other, Magnolioideae, includes a variable

number of genera. Laws (1984) Magnolioideae

included two tribes: Magnolieae, with terminal

flowers, and Michelieae, with axillary flowers.

Nooteboom (1985) and Cheng and Noote-

boom (1993) reduced genera of Magnolioideae

first to six genera (Chen and Nooteboom 1993)

and later to two, and discarded all tribes and

subtribes (Nooteboom 2000). Thus, there is no

disagreement about the status of Liriodend-

roideae containing only Liriodendron; this

isolated placement is also strongly supported

by analyses of nucleotide sequences in which

Liriodendronwas consistently sister to all otherMagnoliaceae (Qiu et al. 1995, Ueda et al.

2000, Shi et al. 2000, Kim et al. 2001). How-

ever, relationships within Magnolioideae

remain equivocal; in all analyses, including

chloroplast DNA sequence data from matK

(Shi et al. 2000), and ndhF (Kim et al. 2001,

2004), the large genusMagnoliais paraphyletic

with respect to the other smaller genera. Li and

Conran (2003) recommended placement of the

smaller genera of Magnolioideae within a

broadly circumscribed Magnolia, but high-lighted the need for more morphological data

to improve phylogenetic resolution within this

group. Many species of Magnoliaceae are

known only from fossils (e.g. Frumin and

Friis 1999, Kim et al. 2004), making combined

morphological and molecular analysis highly

desirable in this group.

The large magnolia flower was once con-

sidered to represent the primitive floral type

(the Ranalian hypothesis), based mainly on the

existence of many fossil forms. However, recent

improved understanding of phylogenetic rela-tionships, together with new fossil discoveries,

have demonstrated that small flowers with

relatively few organs predominate in early-

divergent angiosperms (magnoliids). The large

flowers of Magnoliaceae are now normally

regarded as relatively specialised within this

grade (for reviews see Crane et al. 1994,

Endress 1994a). Here we examine floral

anatomy and ontogeny of a broad taxonomic

range of species of Magnoliaceae in a system-

atic context. The floral morphology of Mag-

noliaceae has been investigated by several

authors, including Baillon (1866), Howard

(1948), Skvortsova (1958) and Melville (1969).

Influential studies of floral vasculature include

those of Canright (1960), Tucker (1961), Skip-

worth and Philipson (1966), Skipworth (1970)

and Ueda (1982, 1986). Earlier work on floral

ontogeny in Magnoliaceae includes

investigations of the floral apex and carpel ofMichelia fuscata (Tucker 1960, 1961), carpel

development inMagnolia stellataand Michelia

montana (Van Heel 1981, 1983), and floral

ontogeny in Liriodendron tulipifera and Mag-

nolia denudata (Erbar and Leins 1994, Leinsand Erbar 1994, Leins 2000).

Materials and methods

Species examined were chosen as representatives of

the taxa with terminal flowers (species ofMagnolia

L.), those with axillary flowers (species ofMichelia

T. Durand) and Liriodendron L. Specimens at a

range of developmental stages were collected either

from the Botanical Garden at the South China

Institute of Botany, Chinese Academy of Sciences(SCBI), or the Living Collections, Royal Botanic

Gardens, Kew (K). Voucher specimens of samples

collected from South China Institute of Botany

were deposited in SCBI. The following species were

investigated: Magnolia championi Benth. (section

Gwillimia) (SCBI: FX Xu 03011), M. delavayi

Franch. (section Gwillimia) (SCBI: FX Xu 03019),

M. grandifloraL. (section Theorhodon) (SCBI: FX

Xu 03008),M. paenetalaumaDandy (SCBI: FX Xu

03014), Michelia crassipesY.W.Law (SCBI: FX Xu

03016), Liriodendron chinense Sargent (SCBI: FX

Xu 03022) and L. tulipifera L. (K: 193977308).Material was fixed in formalin acetic alcohol

(FAA: 70% alcohol, formaldehyde and glacial

acetic acid in a ratio of 85:10:5). For scanning

electron microscope (SEM) examination, buds were

dehydrated in an ethanol series. Dehydrated mate-

rial was then critical-point-dried using a Baltec

CPD 030 critical point drier, mounted onto SEM

stubs using double-sided adhesive tape, coated with

platinum using an Emitech K550 sputter coater,

2 F. Xu and P. J. Rudall: Floral morphology of Magnoliaceae


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and examined using a Hitachi cold field emission

SEM S-4700-II at 45 KV. For light microscope

(LM) observations, material was embedded in resin

prior to sectioning. Fixed flowers and buds were

dehydrated in an ethanol series to absolute ethanol,

then transferred through an absolute ethanol : LRwhite resin series to absolute resin, and kept in a

fridge for about a week, with daily changes of resin.

Specimens were then moved to gelatine capsules

and polymerized between 5862C at 600 mbar

pressure for about 21 hours. Once cooled, the resin

specimens were sectioned at 5lm thickness using a

Leica microtome. Sections were stained in Tolui-

dine Blue and mounted in DPX (Sigma-Aldrich

Co., Gillingham, UK). Photomicrographs were

taken using a Leitz Diaplan photomicroscope with

a digital camera.

Results

Floral morphology and anatomy

Flowers are solitary, bisexual, and haplomor-

phic, i.e. with spirally arranged organs inserted

separately onto an elongated axis. A ring of

three bract-like structures surrounds the flow-

er; these are normally interpreted as bracts, but

sometimes as sepals. The perianth consists of

normally nine free tepals which surround

numerous free stamens and carpels respectively

(Figs. 16).

Androecium. In all species except Lirioden-

dron, the stamens have long slender non-

marginal sporangia which are embedded in

the adaxial surface of the microsporophyll. In

Magnoliaand Michelia species examined here,

the stamen apices (connective appendages) are

short, and there is no distinct filament, so that

the stamens cannot readily be differentiated

into filament, anther, and connective. By

contrast, in Liriodendron the sporangia aremarginal in position and the filaments are

thread-like. At anthesis, sporangia are introrse

in Magnolia and Michelia but extrorse in

Liriodendron. Shape of stamens in Liriodendron

and several Magnolioideae was also studied by

Endress (1994b).Gynoecium. The total number of carpels in

a flower varies between species. In Magnolia

championi and Magnolia paenetalauma, the

number is around ten; but over 90 are present

in Magnolia delavayi (Fig. 1) and 4050 in

Magnolia grandiflora (Fig. 2).

In material examined here, carpels were

entirely separate from each other; no connec-

tion or adnation was observed at any position

in any species examined here (Figs. 8, 9, 20, 21,

30, 31, 36, 37). The carpel-bearing region of

the reproductive apex is cylindrical inMichelia

crassipes, Magnolia championi and Magnolia

paenetalauma to sub-ovoid in Magnolia dela-

vayiand Magnolia grandiflora. InLiriodendron

the carpel-bearing region of the reproductive

apex is more or less conical. This region of the

flower is stipitate, formed by the sterile part of

Figs. 16. Flowers of Magnoliaceae. Fig. 1. Magno-

lia delavayi. Fig. 2. Magnolia championi. Fig. 3.

Michelia crassipes. Fig. 4. Liriodendron tulipifera.

Fig. 5. Magnolia grandiflora. Fig. 6. Magnolia pae-

netalauma

F. Xu and P. J. Rudall: Floral morphology of Magnoliaceae 3


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the carpels, a petiole-like stipe in Michelia

crassipes and all Magnolia species examined,

but not in Liriodendron. In Magnolia champi-

oni, M. paenetalauma and Liriodendron the

carpels are glabrous, but pubescent inMagnolia

grandiflora, Magnolia delavayi and Michelia

crassipes. Each carpel possesses a single style

with three vascular traces, a median and two

ventrals (Figs. 7, 17, 26, 32). Style shape and

length varies from narrow, semi-erect, and

elongated in Magnolia paenetalauma to com-

paratively stout and recurved in Magnolia

grandiflora. In Liriodendron the style is elon-

gate, broad, flattened and wing-like, and con-

tains numerous aggregations of thick-walled

cells (Figs. 34, 40). The extent of the stigmatic

epidermal papillae is variable between species.The stigma inLiriodendrondiffers from that of

species of subfamily Magnolioideae in that it is

small and localized, formed of epidermal

papillae (Fig. 38). Magnolia paenetalauma

(Figs. 10, 11) has a small stigmatic crest of

unicellular epidermal papillae which are longer

than other epidermal cells, whereas in Magno-

lia championi and Michelia crassipes the uni-

cellular epidermal papillae resemble other

epidermal cells (Fig. 24). The ventral suture

of the carpels is not closed in open flowers ofthe Magnolia species examined here (Figs. 22,

23), and only partially closed in Michelia

crassipes, in which the ventral suture is open

at the upper part of style (Fig. 29) but firmly

fused at the lower part (Figs. 27, 28) so that

the line of fusion completely disappears. In

Liriodendron the ventral suture in the style is

completely closed (Figs. 32, 33).

Ovules are inserted at the inner edge of the

carpel margin (see also Erbar 1983). There are

two ovules per carpel in all species examined

here. Crystals were not present in the integu-ments of species examined here, in contrast to

the material examined by Igersheim and En-

dress (1997).Idioblasts and sclereids. Idioblastic (soli-

tary) oil cells were present in all species

investigated here. They are circular and scat-

tered in the carpel parenchyma from the style

to the ovary, in the tissues (Figs. 15, 18) or

subepidermally in Magnolia paenetalauma

(Fig. 12). Mature oil cells are filled with a

large vacuole and a cupule, which is a common

character of oil cells (Mariani et al. 1989), was

observed in some slides (Figs. 15, 18).

Dark-staining tanniniferous cells were

present in most species, although they are

sparse or absent in Michelia crassipes. In

Magnolia championi (Figs. 18, 19, 25) they

are scattered throughout the carpel from style

to ovary and also concentrated under the

epidermis to form a ring of tanniniferous cells.

In Magnolia paenetalauma, tanniniferous cells

are only observed aggregated in the chalazal

region (Fig. 16) or scattered sparsely in the

ovary. In Liriodendron, tannins are present in

the outer integument and the distal portion ofthe inner integument (Fig. 35).

Numerous aggregations of thick-walled

cells or solitary idioblastic sclereids were

observed in all species except Michelia crassi-

pes, also reported for Magnoliaceae by Can-

right (1960), and Igersheim and Endress (1997).

These cells have lamellar thickened walls,

obvious cytoplasm, large intercellular spaces

and well-developed plasmodesmata (Figs. 13,

14). They are distributed from the style to the

ovary in Magnolia championi, Magnoliapaenetalauma and Liriodendron chinense,

although those of the latter possess compara-

tively thinner walls (Fig. 39). In the upper part

of the style ofMagnolia championi, the group of

thick-walled cells are associated with the

median veins, which is not connected in

Magnolia paenetalauma. From the middle part

of style, they are associated with both the median

and lateral veins in these two species. They are

totally free from the veins in Liriodendron.

In confirmation of the observations of

Canright (1960), carpel vasculature is similarin Magnolia and Michelia; the apical carpelsare supplied entirely from the central vascular

cylinder of the axis, while carpels from the

middle to the base are all supplied by both the

cortical and stelar systems. By contrast, in

Liriodendron, all carpels are supplied by

vasculature from both the cortex and central

vascular cylinder.



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Floral development

Floral apex. At initiation, the floral apex is

circular (Figs. 41, 53, 62, 71, 83) in all species

examined, and subsequently develops three

tepals surrounding a triangular floral primor-dium (Figs. 43, 54, 64). During subsequent

floral development the shape of the floral apex

varies from flat during perianth initiation

(Figs. 44, 57, 65) to highly convex at laterfloral stages (Figs. 49, 60, 68, 7476). The later

convex shape of the apex is maintained

through appendage initiations. Tepals,

stamens and carpels are initiated at slightly

different levels around the periphery of the

apex. The members of each group of organs

are initiated closely in time.

Figs. 716. Magnolia paenetalauma. Transverse sections of mature flower. Fig. 7. Floral apex, showing three

fully developed carpels in the last tier, each with 3 vascular bundles (white arrows). Fig. 8. Carpellary region,

showing carpels closely appressed, but not fused. Fig. 9. detail of Fig. 9, showing carpels closely appressed.

Fig. 10. Stigmatic epidermal papillae. Fig. 11. Detail of Fig. 10. Fig. 12. Subepidermal oil cell. Fig. 13. Upper

carpels, showing aggregations of thick-walled cells in each carpel. Fig. 14.Detail of thick-walled cells in Fig. 13,

free from the vascular bundles. Fig. 15.Oil cell (black arrow). Fig. 16.Tanniniferous cells in chalazal region of

ovule. All bars = 50 lm



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Figs. 1725 Magnolia championi. Transverse sections of mature flower. Fig. 17. Single carpel, showing three

vascular traces (black arrows) interspersed with regions of thick-walled cells. Fig. 18. Oil cell and tanniferouscells. Fig. 19. Single carpel, showing aggregations of thick-walled cells and subepidermal tannins. Fig. 20.

Carpels including ovules; carpels closely appressed but not fused to each other; note insertion to axis. Fig. 21.

Detail of Fig. 20, showing carpels closely appressed. Fig. 22. Carpel below ovule, showing ventral suture.

Fig. 23. Detail of Fig. 22, showing open ventral suture. Fig. 24. Stigma, showing unicellar epidermal papillae.

Fig. 25. Tanniniferous cells (arrowed) in chalazal region of ovule. All bars = 50 lm



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Tepals. The three outer tepals are initiated

in sequence (Figs. 42, 56, 59, 63) but ultimately

form a single whorl (Figs. 43, 54, 64). At this

stage, the shape of the floral primoridum

changes from circular to triangular (Figs. 43,

54, 64). The second whorl of three semicircular

tepal primordia are initiated at the tips of the

three angles formed by the triangular floral

primordium and alternate with the outer tepal

whorl (Figs. 44, 57, 65). One of them is

initiated slightly earlier than the other two

(Figs. 6567). Similarly, the innermost third

whorl of three perianth primordia differ

slightly from one another in time of initiation

and alternate with those of the middle whorl

and hence are opposite those of the first whorl

(Figs. 45, 46, 68, 72, 73). Thus, the tepals are

initiated in spiral acropetal succession, but are

trimerously whorled; the internodes between

petals seldom elongate. There is a considerable

difference in size between primordia of the first

and the second whorl during early stages

(Fig. 73). Following completion of tepal initi-

ation, the central floral primordium is more or

less circular (Figs. 4749, 68, 7476).

Stamens. Stamen primordia are initiated

at the same time or slightly later than the third

whorl of perianth primordia. One or two

stamen primordia arise opposite (in the same

sector as) the first tepal primordia (Figs. 46,

47, 68). Stamens are initiated acropetally,

successively and rapidly around the base of

the apex (Figs. 48, 49, 60, 76, 77, 84). The

order of stamen initiation within each whorl is

Figs. 2631. Michelia crassipes.Transverse sections of mature flower. Fig. 26.Single carpel, with three vascular

traces (black arrows); thick walled cells absent; the ventral suture is closed. Fig. 27.Lower part of style.Fig. 28.

Detail of Fig. 27, showing closed ventral suture. Fig. 29. Upper part of style, showing open ventral suture.

Fig. 30. Carpellary region, showing free carpels. Fig. 31. Detail of Fig. 30. All bars = 50 lm



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Figs. 4152. Magnolia paenetalauma. Floral development (SEM). Figs. 4143. Differentiation of three outer

tepals surrounding the triangular floral apex. Fig. 44. Differentiation of second tepal whorl, one tepal slightlyearlier than the other two. Fig. 45. Initiation of three outer and three middle tepals, and first tepal of inner

whorl. Figs. 4648. Differentiation of third tepal whorl and stamens. Fig. 49. Acropetal initiation of stamens.

At this stage the floral apex reaches its greatest height and diameter.Fig. 50.Differentiation of carpels, showing

carpel primordia larger than those of stamens. Fig. 51.Differentiation of carpels, showing the carpel primordia

initiated alternately and in series of four to five. Fig. 52.Older stage. Abbreviations:c= carpel;f= floral apex;

s= stamen;t1= tepal of first whorl;t2= tepal of second whorl;t3= tepal of third whorl. All bars = 100 lm



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not determined. During stamen development,

the floral apex displays its greatest height and

diameter. In Liriodendron tulipifera and Mag-

nolia delavayi the outermost stamens are

broader and petaloid at older stages (Figs. 61,

88).

Carpels. When all stamen primordia have

been initiated and begun to broaden, the

remaining floral apex becomes slightly flatter.

Some rounded bulges are initiated in series of

four to five, which are larger than the stamen

primordia (Figs. 50, 51, 55, 69, 78, 80, 81, 85,

86). Carpel primordia are free and are initiatedin acropetal succession (Figs. 50, 51, 58, 69, 70,

79, 87). During carpel initiation, the floral apex

gradually diminishes in height and diameter.

At the middle or late stage of ontogeny, the

margins of each carpel are incurved, forming a

deep ventral groove which extends to the tip

(Figs. 51, 55, 58, 7982, 87, 88). There is no

differentiation of stigma and style at this stage.

In older buds of all species examined here,

stamens and carpels are arranged irregularly

on the floral axis (Figs. 52, 61, 70, 82, 88).

Figs. 5361. Magnolia delavayi. Floral development (SEM). Figs. 53, 56, 59. Differentiation of outer tepals.

Fig. 54. Three outer tepals initiated surrounding triangular floral primordium. Fig. 55. Differentiation of

carpels, showing carpel primordia initiated in series of four to five. Fig. 57. Initiation of three middle tepals.

Fig. 58. Differentiation of carpels, showing deep ventral groove extending to the tip of each carpel. Fig. 60.

Initiation of stamens. Fig. 61. Older stage of flower bud, showing arrangement of stamens and carpels, and

outermost petaloid stamens. Abbreviations: c = carpel; f= floral apex; s = stamen; ps = petaloid stamens;

t1= tepal of first whorl; t2 = tepal of second whorl; t3 = tepal of third whorl. All bars = 100 lm



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Discussion

Our observations correspond with those of

other investigations, such as Tuckers (1961)

observations on Michelia fuscata, that apical

growth continues during floral development inMagnoliaceae, but the floral apex gradually

diminishes in diameter and height during

carpel initiation. Thus, the flower of Magnoli-

aceae is not a true determinate structure,

since it does not terminate in an organ or

organ whorl, as in typical eudicot flowers.

Rather, the floral meristem achieves determi-nacy by gradual diminution (Tucker 1960,

1979), as with the indeterminate apex of

racemose inflorescences.

Floral ontogeny in Magnoliaceae is remark-

ably homogeneous throughout the family, with

tepals arranged in a more or less whorled

pattern surrounding more or less irregularly

arranged fertile organs. Erbar and Leins (1994)

observed an intermediate organisation in

Magnolia denudataand Liriodendron tulipifera,

Figs. 6270. Magnolia cha (SEM). Fig. 62. Floral apex. Fig. 63. Differentiation of first tepal of outer whorl.

Fig. 64.Subsequent differentiation of outer tepal whorl surrounding the triangular floral primordium. Fig. 65

67.Differentiation of middle tepal whorl, one tepal slightly earlier than the other two. Fig. 68. Initiation of

stamens (arrow). Fig. 69. Differentiation of carpels, showing the carpel primordia initiated in series of four to

five.Fig. 70. Older stage, showing irregular arrangement of stamens and carpels. Abbreviations: c = carpel; f

= floral apex;s = stamen;t1= tepal of first whorl;t2= tepal of second whorl; t3= tepal of third whorl. All

bars = 100 lm



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Figs. 7182. Magnolia grandiflora. Floral development (SEM). Fig. 71. Floral apex. Figs. 7273. Initiation of

three tepal whorls. Fig. 7476.Initiation of third tepal whorl and stamens. At this stage the floral apex reachesits greatest height and diameter.Fig. 77.Acropetal initiation of stamens. Fig. 78.Initiation of carpels, showing

carpel primordia larger than stamen primordia. Figs. 7981. Differentiation of carpels, showing carpel

primordia initiated alternately, and in series of four to five. A deep ventral groove extends to the tip of each

carpel. The floral apex gradually diminishes in height and diameter. Fig. 82.Older stage of flower bud, showing

irregular arrangement of stamens and carpels. Abbreviations: c = carpel; f= floral apex; s = stamen; t1 =

tepal of first whorl; t2 = tepal of second whorl; t3 = tepal of third whorl. All bars = 100 lm



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and suggested that a whorled condition is

derived from a spiral one in basal angiosperms

(Erbar 1983, 1988; Erbar and Leins 1982, 1983,

1994). In some Magnolioideae not examined

here, such as Pachylarnax, Dugandiodendron,

andWoonyoungia(Li and Conran 2003) carpel

number is reduced to less than ten. Van Heel

(1983) described early carpel formation in

Michelia montana, which is unusual in possess-

ing only two to four stalked carpels arranged in

pairs.

One outstanding question of floral mor-

phology in Magnoliaceae is whether the out-

ermost organs represent bracts, as indicated by

their mature structure, or tepals, as Ueda

(1986) proposed. The three distinct outermost

organs are initiated in sequence, but ultimatelyform a single whorl; thus their ontogeny is

consistent with a tepal interpretation.

Both species ofLiriodendronexamined here

differ from other Magnoliaceae in that the

carpels are entirely closed at maturity, resulting

in a relatively small stigma, in contrast to the

elongate stigma of most species of Magnolia.

No carpel fusion was observed here in species of

Magnolioideae, either in primordial or mature

structures. In some other early-diverging an-

giosperms, including the ANITA grade and

some magnoliids (Endress and Igersheim 2000),

carpel closure is entirely by secretion rather

than by postgenital fusion. However, this char-

acter may be variable in Magnoliaceae, and

requires further investigation. Nooteboom

(1985) reported carpel fusion in some of the

smaller genera of Magnolioideae, such as Tal-

auma, Aromadendron and Tsoongiodendron, in

which the fruit is a syncarp. Li and Conran

(2003) reported that in all Magnoliaceae thecarpels are connate to varying degrees before

dehiscence; this conflicts with our data, but

indicates that some late fusion or concrescence

may occur. In Michelia crassipes, the ventral

Figs. 8388. Liriodendron tulipifera. Floral development (SEM). Fig. 83. Floral apex. Fig. 84. Initiation of

stamens. Figs. 85, 86. Initiation of carpels, showing carpel primordia initiated in series of four to five. Fig. 87.

Carpel differentiation, showing a deep ventral groove extending to the tip of each carpel; the floral apex

gradually diminishes in height and diameter. Fig. 88. Older stage of flower bud, showing arrangement of

stamens and carpels, and outermost petaloid stamens. Abbreviations:c= carpel;f= floral apex;ps= petaloid

stamen; s = stamen. All bars = 100 lm



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carpel suture is closed in the lower part of the

style, so that the stigmatic region is relatively

short. Michelia crassipes also differs from the

other species examined in the absence of thick-

walled cells and tannins. Wider sampling is

necessary to determine the significance of these

characters. However, we concur with Noote-

boom (1985) that concrescence of the carpels

alone is not a reliable character for delimitation

of genera in Magnoliaceae.

We thank Chrissie Prychid (Royal Botanic Gar-

dens, Kew) for help in the laboratory. The project

was supported by the National Sciences Founda-

tion of China (grant number 30000011, 30370108)

and the National Sciences Foundation of Guang-

dong province, China (grant number 000991). We

are grateful to Peter Endress and an anonymous

reviwer for their comments on the manuscript.

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Addresses of the authors: Fengxia Xu (e-mail:

[email protected]), South China Botanical Garden,Academia Sinica, Guangzhou, 510650, China.

Paula J. Rudall (e-mail: [email protected]),

Royal Botanic Gardens, Kew Richmond, Surrey,

TW9 3AB, UK.



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