Morphology and Anatomy of the Flower of Meliosma (Sabiaceae)- Implications for Pollination

Morphology and anatomy of the flower of Meliosma (Sabiaceae):implications for pollination biology

L. P. Ronse De Craene,1 L. Wanntorp2

1Royal Botanic Garden Edinburgh, Edinburgh, UK2Swedish Museum of Natural History, Stockholm, Sweden

Received 29 June 2007; Accepted 9 October 2007; Published online 7 December 2007

� Springer-Verlag 2007

Summary. The structure and anatomy of mature

flowers of four species of Meliosma is investigated

using scanning electron and light microscopy. The

vasculature of the flower, including the structure of

the gynoecium, is described in detail. The mechanism

of stamen maturation and pollen release is illustrated

and discussed. The existence of an explosive pollina-

tion mechanism is questioned for at least part of the

species. Flowers are proterandrous and fertile stamens

are kept spatially separate from the style by a ring of

large staminodes. Anthers are disporangiate by the

loss of the adaxial pollen sacs. During maturation the

filament bends progressively outwards and releases

the pollen on the extension of the connective that acts

as a secondary pollen presentation system. The

nectary has five appendages topped with stomata

secreting abundant nectar. The relationships of Sabi-

aceae are discussed relative to other early diverging

eudicots. The significance of Sabiaceae as an isolated

clade is highlighted, although some features point to a

link with Menispermaceae.

Keywords: Meliosma; Sabia; Sabiaceae; early

diverging eudicots; disporangiate anthers; floral anat-

omy; staminodes; nectary; pollination

Introduction

The Sabiaceae is a small family of three genera

Sabia Colebr., Ophiocaryon Endl. and MeliosmaBl. distributed in Eastern and South Eastern Asia

and tropical Central and South America. Melios-ma with about 25–70 species has the widest

distribution occurring both in Asia and America,

while Sabia with about 19–50 species is

restricted to Asia, and Ophiocaryon with about

7 species is only found in tropical South America

(Chen 1943, van Beusekom 1971, Barneby 1972,

Kubitzki 2007). Occasionally two separate fam-

ilies Sabiaceae and Meliosmaceae have been

considered (e.g. Dahlgren 1981, Takhtajan 1997),

although a unified Sabiaceae is to be preferred

(e.g. Warburg 1895, Cronquist 1981, Stevens

2007).

Earlier classifications placed Sabiaceae either

in the Sapindales (e.g. Bentham and Hooker

1862, Dahlgren 1981, Takhtajan 1997), or in the

Ranunculales close to Menispermaceae (e.g.

Warburg 1895, Cronquist 1981). However, all

recent phylogenetic studies based on molecular

Correspondence: Louis P. Ronse De Craene, Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK

e-mail: [email protected]

Pl Syst Evol 271: 79–91 (2008)

DOI 10.1007/s00606-007-0618-y

Printed in The Netherlands

Plant Systematicsand Evolution

data have placed the family in the early diverging

eudicots, but uncertainties remain about its

position relative to Proteales and Buxales, or

even core eudicots (e.g. Hilu et al. 2003; Soltis

et al. 2003, 2005; Furness et al. 2007; Worberg

et al. 2007).

Wanntorp and Ronse De Craene (2007)

investigated the floral development of selected

species of Meliosma and found that the pentam-

erous flowers of Sabiaceae have a unique origin

with a spiral initiation throughout, adding support

to the hypothesis that pentamery has arisen

independently in the family.

The flowers of Meliosma are deceivingly

complex (Wanntorp and Ronse De Craene

2007). They consist of four to five small sepals,

five petals of two different sizes, three stamin-

odes, two fertile stamens, and a superior,

bicarpellate ovary. The staminodes are situated

opposite the large petals and are basally adnate

to them. The stamens are dorsally fused with a

small petal. Stamens and staminodes are

arranged in a closely coherent unit. Anthers

consist of a broad basal platform, in some

species extending into a crenulate rim, and bear

two globular pollen sacs in an apical-adaxial

position. The platform goes over into a narrow

flattened filament. Staminodes form pouches in

which the globular pollen sacs fit tightly when in

bud. Two of the staminodes are asymmetrically

built because only one pouch is developed, and

the odd one has two pouches. The four pollen

sacs fit with these four pouches. The staminodes

form a tightly connected rim encircling the style.

The gynoecium consists of two fused carpels

with two connivent, occasionally twisted styles.

The base of the ovary is surrounded by a

conspicuous nectary with five prominent

appendages alternating with the stamens and

staminodes. A floral diagram illustrating the

arrangement of floral parts is given in Wanntorp

and Ronse de Craene (2007).

Descriptions of the morphology of the flowers

of Meliosma often lack detail and are inaccurate

(e.g., Gagnepain 1950, see Discussion in Wann-

torp and Ronse De Craene 2007). Little is known

about the pollination of the tiny flowers and

almost nothing is known regarding the anatomy

of the flower. Warburg (1895) and van Beusekom

(1971) argue that the flowers of Meliosma have

an explosive pollination mechanism, whereas the

stamens are held under tension by the staminodial

appendages. In this study we analyze the floral

anatomy and the mature morphology of selected

species of Meliosma to understand the internal

structure of the flower and clarify the pollination

mechanism. Comparison is made with the flower

of the sister genus Sabia. Knowledge of the floral

morphology of families of the early diverging

eudicots becomes increasingly important to

understand the floral evolution of the angio-

sperms. This paper aims to contribute to that

goal.

Materials and methods

Flower buds of four species of Meliosma were used:

M. veitchiorum Hemsl. (accession number 19521006),

M. dilleniifolia (Wall.) Wall. aff. ssp. tenuis (Maxim.)

Beus. (accession number 19632056; M. dilleniifolia(Wall.) Wall. ssp. cuneifolia (Franch.) Beus. (syn. M.cuneifolia Franch., also used by Wanntorp and Ronse

De Craene 2007: accession number 19381038) in

cultivation at the Royal Botanic Garden Edinburgh

(RBGE), and M. pinnata (Roxb.) Walp. ssp. arnotti-ana (Walp.) Beus. var. oldhamii (Maxim.) Beus. (syn.

M. oldhamii Maxim.) from Kyoto Botanical Garden

(Japan). Floral buds were collected, fixed in FAA (5%

acetic acid, 5% formaldehyde, 90% ethanol 70%), and

subsequently stored in 70% alcohol. Additional

observations were made on flowering trees of M.veitchiorum and M. alba (Schlechtend.) Walp. (syn.

M. beaniana Rehd. & Wils.: accession number:

19081007) cultivated at RBGE. Meliosma veitchiorumand M. alba belong to subgenus Kingsboroughia,

while M. dilleniifolia and M. pinnata belong to

subgenus Meliosma. Buds and mature flowers were

dissected and prepared using a Wild MZ8 stereo-

microscope (Leica, Wetzlar, Germany), dehydrated in

an ethanol–acetone series, and critical point dried with

a K850 Critical Point dryer (Emitech Ltd, Ashford,

Kent, UK). The dried material was later coated with

platinum using an Emitech K575X sputter coater

(Emitech Ltd, Ashford, Kent, UK) and examined with

a Supra 55VP scanning electron microscope (LEO

Electron Microscopy Ltd, Cambridge, UK). Reference

material (in ethanol) (831 Led, 832 Led, 833 Led, 876

Led) is kept at RBGE.

80 L. P. Ronse De Craene, L. Wanntorp: Floral anatomy and pollination mechanism in Meliosma

For light microscopy flower buds were embedded

in Kulzer’s Technovit (2-hydroxyethyl methacrylate),

as described in Igersheim and Cichocki (1996) and

sectioned with a Leitz Minot 1212 rotary microtome

fitted with metal blade. The sections (about 8 l thick)

were stained with ruthenium red and toluidine blue

and enclosed in DMX.

Results

Floral anatomy. Floral anatomy was investigated

in flower buds of Meliosma veitchiorum, M.pinnata, and M. dilleniifolia ssp. cuneifolia. No

separate descriptions are given for individual

species as anatomy was generally found to be

similar. A closed vascular system is found at the

base of the flower. Traces for sepals and bracts arise

at different levels corresponding to their initiation

sequence. The five sepals are supplied by a single

vascular trace that divides into one median and two

laterals higher in the sepal (Fig. 1). Five common

stamen–petal traces are given off at a higher level

following the departure of sepal traces (Fig. 2).

Stamens/staminodes and the corresponding petals

are detached as common organs and the vascular

bundles branch off into the respective organs (Figs.

3, 4). The division of bundles to the stamens occurs

below that of the staminodes. At this level a nectary

is visible as small-celled tissue and two traces

diverge from the central stele (Fig. 4, arrows). The

gynoecium is delimited from the nectary and the

two traces differentiate as the two dorsal bundles of

the carpels (Figs. 4, 5). While the locules are visible

the central vascular tissue becomes reorganized in

two areas, each becoming the ventral traces for the

respective ovules of each carpel by halving (Figs. 5,

6, 12). The ventral traces are used up in supplying

the ovules. At the top of the ovary the dorsals fade

out and no traces run into the styles. Ovules are

initially inserted parallelly (only one of a pair

visible in Fig. 10) but in older buds they become

superposed and a septum separates the two locules

(Figs. 11–13, 15). The ovules fill the ovarian cavity

completely. The placenta is covered with darkly

staining secretory trichomes (Fig. 13) and secretion

extends along the whole stylar canal (Fig. 16). In M.pinnata and M. dilleniifolia the ovules have a single

integument (Figs. 11, 12, 15, 16). In M. veitchiorum

two integuments are formed as a rim around the

nucellus (Figs. 6, 14, 17). We occasionally found

that the outer integument is incompletely

developed, suggesting that the single integument

is the inner one in M. pinnata and M. dilleniifolia.

The styles extend beyond the ring of staminodes

(Figs. 8, 9, 18). Styles are weakly to strongly

appressed but not fused (Figs. 9, 18, 39–42). In M.pinnata and M. dilleniifolia the two styles are erect

and terminate in a common slit-like stigmatic area

(Figs. 9, 39, 40, 42). Styles are not closely

appressed to each other and are often intertwined

in M. veitchiorum (Fig. 27). No vascular tissue runs

in the styles but the two stylar canals are filled with

a secretion (Fig. 18). At the top of the styles the

stylar canals open adaxially into a broad slit. Anther

development has been described in Wanntorp and

Ronse De Craene (2007). Ovule development

corresponds with microsporogenesis (Fig. 25). In

young anthers the anther wall is composed of an

epidermis, an endothecium which is one cell thick,

a few intermediate layers, and an inner secretory

tapetum layer of the secretory type (Figs. 19, 20). In

older anthers the tapetum layer is partly resolved

and the endodermis shows tangential thickenings

(Figs. 21–23). The ovary wall, as well as the

anthers, contains cells with a broad prismatic

calcium oxalate crystal. In the anthers these are

mainly situated in the area of the vascular bundle

(Figs. 23, 24). By disintegration of the anther wall,

the crystals become intermingled with the pollen.

Pollen grains are tricolporate, about 15 l in size,

and with a reticulate exine.

Flowering process. Flowers are proter-

androus. There is a difference to the extent of

development of the style between different

species. In M. veitchiorum and M. pinnata the

styles grow between the tightly connivent

staminodes before the buds opens (Figs. 18,

27). In M. dilleniifolia ssp. cuneifolia the

development of the style lags behind and the

closely interconnected styles emerge when the

anthers are already open (Figs. 28, 30, 36). In

young flower buds the staminodes surround the

young styles in a coherent unit and the young

anthers fit in adaxial folds formed by the

staminodes (Figs. 9, 27, 36). At this stage the

filaments are abruptly bent inwards in the middle

L. P. Ronse De Craene, L. Wanntorp: Floral anatomy and pollination mechanism in Meliosma 81

and the anthers are hidden from view (Fig. 27).

One of the three staminodes is symmetrically

developed and encapsulates one pollen sac of

each anther; the two other staminodes have only a

single lobe that encloses the other pollen sac

(Figs. 6, 8, 26, 36). In this way the androecium

forms a tightly closed dome covering disc and

ovary. When the flowers open, the style protrudes

between the staminodes before the stamens are

clearly visible. By pressing on the filament with a

needle, the anthers pop out of the pouch formed

by the staminodes (Figs. 27–30). When the flower

expands, the filaments bend outwards and the

anthers become detached from the tight grip of

the staminodes. This is a progressive process in

M. veitchiorum and M. alba, as we could not see

the explosive mechanism described by van

Beusekom (1971) and Warburg (1895). In M.dilleniifolia we often found fewer stamens in

opened flowers (Figs. 28, 30), suggesting that

they drop off at an early stage, possibly by an

explosive mechanism. While the filaments curve

outwards the pollen sacs dehisce by a slit situated

on the inner surface (Figs. 27, 28, 30, 34, 35).

The single pollen sacs open inward out; the

anther wall curves outwards and exposes the

pollen grains that are collected in clumps on the

broad connective expansion (Figs. 29, 34, 35).

This broad dish-like area differs in shape between

different species, being shallow and extending as

flaps next to the pollen sacs in M. veitchiorum(Figs. 9, 27), and forming two ventral auricles in

M. dilleniifolia (Figs. 31–33) and M. pinnata(Fig. 34). The sticky pollen remains in clumps on

the protuberance for the insect visitor to collect

(Figs. 29, 34). When pollen is released the

anthers continue their outward curve (Fig. 30).

Soon after pollen release the stamens and

staminodes drop off with the petals. The

pollination mechanism might explain the

heteromorphy of the petals; the broad erect

petals enclose the bud and hold the staminodes

erect (Figs. 27, 28), while the smaller often bifid

petals do allow for the filament to curve outwards

(Figs. 32, 33). After the flower has dropped its

petals and stamens the ovary continues its

development sheathed by the nectary. The

ovary wall is covered with uniseriate multi-

cellular trichomes (Fig. 44).

The nectary in Meliosma is a broad disc

surrounding the superior ovary. There is no

vascular tissue but the secretory cells are small

with large nuclei (Figs. 4, 12, 18, 25, 38). At

maturity the nectary is either developed in the

shape of a tire or a buoy with weak crenellations

(Fig. 41), or it resembles a crown bearing five

prominent appendages topped with one to three

stomata (Figs. 39, 40, 43). Both types were

observed in M. dilleniifolia (Figs. 40, 41), while

in the other species only the crenulate disk was

found. Abundant secretion occurs through these

distal stomata (Figs. 45, 46). The appendages are

not equidistant, but four are grouped in pairs, while

the odd one is situated at the other end of the disc

(Figs. 40, 43). The arrangement of appendages

corresponds with the insertion of the stamens—the

pairs are close to the fertile stamen in the median

plane of the flower. As the staminodes tightly

Figs. 1–14. Transverse and longitudinal sections of the flower of Meliosma. 1, 7, 8, 10–13 M. dilleniifolia ssp.

cuneifolia; 2–6, 9, 14 M. veitchiorum. 1 TS at base of flower with departure of traces to each sepal (arrows). 2, 3Successive TS with departure of common petal–stamen traces (arrows). 4 Division of stamen petal traces and

separation of respective organs. Note nectary and departure of two dorsals (arrows) from the central stele. 5 TS

through the upper part of the nectary. 6 TS through the middle of the ovary with ovule attachment. 7 TS through

the upper part of the ovary. 8 TS through the base of the style. Note the connected staminodes. 9 TS through the

stylar and anther regions. 10 Young ovary showing one of the developing ovules. 11 Section of older ovary

showing two ovules within a locule. 12 TS in the lower part of the ovary showing two ovules and the nectary. 13TS through the middle of the ovary with placental tissue. The arrow points to secretory trichomes. 14 TS of one

locule showing an ovule with two integuments and attachment to the placenta. 1–3, 5–9 Bar 50 lm, 4 12,

13 = 20 lm; 10, 11 = 100 lm. Af fertile stamen, As sterile stamen, D dorsal trace, Ii inner integument, Nnectary, Nu, nucellus, Oi outer integument, Ow ovary wall, P petal or petal trace, S sepal, St style, V ventral trace.

Asterisks point to the adaxial side of the flower

b


cover the nectary as a lid (Figs. 6–8,38), nectar is

produced and accumulates between the broad

disc lobes. Access to nectar is only possible

through slits between the staminodial lobes—this

induces the pollinating insects to wander close to

the anther tissue.

Discussion

Anther dehiscence. The broad dish-like append-

age of the anthers has been described as an

expanded connective by various authors (e.g.

Baillon 1874, Warburg 1895, Takhtajan 1997).

However, the fact that the anthers are

disporangiate has been overlooked by most

authors (except for brief mentions in the

literature (e.g. Warburg 1895, Baillon 1874;

Chen 1943, Kubitzki 2007). Sabiaceae were

left out in the global review of anthers of

Endress and Stumpf (1990). Sabia shares the

disporangiate anthers with Meliosma (Ronse De

Craene unpubl. obs.; van de Water 1980). One

tricky question is whether the adaxial or the

abaxial pair of pollen sacs is reduced.

Developmentally it is not possible to observe

any traces of the second set of pollen sacs

(Wanntorp and Ronse De Craene 2007). The

normal dehiscence pattern for tetrasporangiate

anthers in most angiosperms is laterally with the

lobes curving towards the exterior (Fig. 47A).

When dehiscing, the anther walls of Meliosmacurve inward out, exposing the pollen on the

broad connective. A plausible explanation for

this pattern is that the adaxial (ventral) pollen

sacs have been lost and that the broadened

connective has pushed the two remaining pollen

sacs towards each other (Fig. 47B). In the case of

tetrasporangiate anthers opening in a similar

fashion one would expect the abaxial pollen sacs

to curve out in the same way as in Meliosma.

Van de Water (1980) described a similar

dehiscence pattern for Sabia. Sabia has a

broad connective; the anthers open along the

connection with the connective at the adaxial

side and the wall turns inside out. When fully

opened the anthers give the impression of being

extrorse. Disporangiate anthers are fairly

common in basal angiosperms (e.g. Lauraceae,

Monimiaceae, Hernandiaceae) and their location

is difficult to assess. They have been correlated

with a specialized floral biology such as a

secondary pollen presentation on the gynoecium

or a precise deposition of pollen linked to the

dehiscence of the thecae by narrow slits (Endress

and Stumpf 1990). In the case of Meliosma the

anthers are set widely apart and separated by the

broad staminodes; pollen is not deposited on the

gynoecium, but on the extended connective

appendage. It appears that Meliosma shows a

unique pattern of secondary pollen presentation

by accumulating pollen on the extensive

connective-dish. The gradual movement of the

anthers exposes the dish to visiting insects.

However, more experimental work needs to be

carried out in other species to verify the

statement of van Beusekom whether an

explosive mechanism can be invoked. In that

case the broad connective can act as a container

catapulting the pollen on the insect. Zhilin (1981)

suggested that the explosive mechanism is

restricted to subgenus Meliosma to which M.dilleniifolia and M. pinnata belongs. Subgenus

Kingsboroughia containing M. veitchiorum and

M. alba is said to lack the explosive mechanism

Figs. 15–26. Transverse and longitudinal sections of the flower of Meliosma. 15, 16, 18 M. pinnata; 17, 19–26M. veitchiorum. 15 LS showing two superposed ovules. In the upper ovule an embryo sac is visible (arrow). 16TS through locule. Note the single integument and secretory hairs on the placenta (arrow). 17 TS with detail of

ovule with two integuments. 18 LS through young flower. Note the style filled with secretion reaching into the

ovary (arrow). 19 LS of anther at meiosis. 20 LS of anther wall. 21 LS of mature anther. 22 TS of anther wall. 23TS through the middle of mature anther. Arrow points to the position of calcium oxalate crystals. 24 Detail of

cells in the connective area. 25 LS of part of the flower showing two superposed ovules. 26 Adaxial view of

staminode with two interconnected petals. 18, Bar = 50 lm, Figs. 19, 21, 23 = 10 lm, 15–17, 20, 22,

24 = 20 lm, 26 = 200 lm. Af fertile stamen, As sterile stamen, En endodermis, Ep epidermis, Ii inner

integument, N nectary, Nu, nucellus, Oi outer integument, P petal, Ta tapetum, V ventral trace

b


and the flowers remain open for a longer time.

This corresponds with our observations.

Floral anatomy. The ovary is syncarpous

but the styles are postgenitally united. The ovules

are initially positioned side by side in each locule

but they become superposed by the restricted

space for their further development. The

embryology of Sabiaceae has been briefly

described by Mauritzon (1936), Raju (1952),

and Sharanina (1996). They mention that the

ovules are unitegmic and have no micropyle. We

report the presence of two integuments in

Meliosma veitchiorum, contrary to descriptions

of unitegmy in textbooks obviously taken over

from earlier studies (e.g. Cronquist 1981,

Takhtajan 1997). However, the other species

studied were unitegmic. Endress and Igersheim

(1999) briefly described the gynoecium structure

of Sabia and reported the presence of mucilage in

style and ovary. We report the presence of intra-

ovarian secretory trichomes situated on the

placenta. These trichomes produce ovarian

mucilage which is also found in the pollen-

transmitting tract of the style and play an obvious

role in facilitating pollen tube growth (Rudall

et al. 1998). Secretory intra-ovarian trichomes are

rare in the eudicots, but are found more regularly

in the monocots and some basal angiosperms.

There is no discussion on crystals in anthers,

but Raju (1952) mentions crystals in the ovary

wall cells. We found that calcium oxalate crystals

were often present in open anthers mixed with

pollen grains. D’Arcy et al. (1996) studied the

presence of calcium oxalate in anthers of differ-

ent families, not including Sabiaceae. Contrary to

species where calcium oxalate occurs in packages

at the level of anther dehiscence, in Meliosma

calcium oxalate occurs scattered in idioblasts

around the connective area. D’Arcy et al. (1996)

discussed several hypotheses for the presence of

calcium oxalate packages, including a role in

anther dehiscence, as a metabolic sink, discour-

agement of herbivores or as a food source. It is

possible that the association of calcium oxalate

with pollen in Meliosma is accidental without the

significance of the packages associated with

specialized flowers found in the asterids.

The apical stomata on the nectary have been

overlooked by most authors, who describe disc

and glands, and nectaries as separate entities (e.g.

Chen 1943). The whole disc-like structure with

appendages needs to be described as a nectary, as

it contains densely staining tissue responsible for

nectar secretion. Chen (1943) and van de Water

(1980) observed a similar variation in the nectary

of Sabia as in Meliosma in the extent of

development of the appendages, as well as

presence of glandular tissue on top of the

appendages.

Systematic considerations. The flower mor-

phology of Meliosma is reminiscent of Sabia in

many ways and supports the recognition of a

single family (Chen 1943, van de Water 1980,

Kubitzki 2007, Wanntorp and Ronse De Craene

2007). Sabia and Meliosma share several floral

characters including the filaments adhering to the

base of the petals, disporangiate anthers with a

similar pollen morphology, the five-lobed

nectary, and similar ovary and ovules. The

connective in Sabia is thick, although not

developed to the extent found in Meliosma. A

comparative study including the polarization of

character evolution will only be possible by

including the third genus of Sabiaceae,

Figs. 27–38. Anthesis and anatomy of staminodes in Meliosma. 27, 29, 38 M. veitchiorum; 28, 30–33, 35–37:

M. dilleniifolia ssp. cuneifolia; 27, 34: M. pinnata. 27. Lateral view of flower at anthesis, two petals and two

staminodes removed. The right anther starts dehiscing (arrow). 28 Apical view of flower at the onset of

dehiscence. 29 Pollen grains on the exposed anther wall. 30 Flower with recurved filament. 31–33 adaxial,

lateral, and abaxial views of young anthers and their associated petals. 34 Dehisced anther with pollen grains on

the basal appendage. 35 TS of dehisced anther with pollen grains and the connective. 36 TS of staminodes

surrounding the style. 37 TS of two connected staminodes. 38 LS of nectary partly covered by staminodial

appendage. 35, 37, Bar = 20 lm, 36, 38 = 50 lm, 34 = 100 lm, 30–33 = 200 lm, 29–31 = 500 lm,

28 = 1 mm. Af fertile stamen, As sterile stamen, N nectary, P petal. Asterisks point to the adaxial side of the

flower

b


Ophiocaryon, for which material is currently not

available.

Affinities of Sabiaceae are still unclear.

Table 1 compares Sabiaceae with other poten-

tially related families in a number of characters.

A closer link with Menispermaceae (cf. Cron-

quist 1981) cannot be excluded based on pollen,

embryological and ovary characters. Some Meni-

spermaceae share dithecal anthers with Sabiaceae

(Endress and Stumpf 1990) but details of their

arrangement are not known. Interestingly some

Menispermaceae and Ranunculaceae have

unitegmic ovules with a rudimentary outer

integument (reported in Endress and Igersheim

1999). Sabiaceae share the presence of hemian-

atropous ovules with Menispermaceae and some

Figs. 39–46. Nectary and gynoecium in Meliosma. 39, 42, 43 M. pinnata; 40–41 M. dilleniifolia ssp.

cuneifolia; 44 M. veitchiorum; 45–46 M. dilleniifolia ssp. aff. tenuis. 39 Lateral view of flower without petals or

stamens. 40 Apical view of ovary with nectary and appendages. 41 Apical view of ovary with nectary. Note the

small, almost undeveloped appendages. 42 Stigmatic hole. 43 View of nectary from above—ovary removed. 44Detail of trichomes on the ovary wall. 45 Nectary appendage with one of the apical stomata visible. 46 Nectary

appendage covered with secretion. 42, 44, Bar = 20 lm, 45, 46 = 50 lm, 43 = 100 lm, 39 = 200 lm, 40,

41 = 500 lm. Asterisks point to the adaxial side of the flower


Fig. 47. Diagrammatic presentation of anther dehiscence of common tetrasporangiate anthers (A) and

disporangiate anthers of Sabiaceae (B). The adaxial side below, the abaxial side up

Table 1. Comparison of Sabiaceae with other early diverging eudicots on a number of selected floral characters

Characters Sabiaceae Menispermaceae Proteaceae Buxaceae Trochodendraceae

Common stamen–

petal (tepal) trace

+ ? + – +

Carpel number 2 (1)2–6 1 2–3 4/6-17

Nectary position Intrastaminal

disc

Petal Intrastaminal disc

lobes

Pistillode or

ovary

Ovary

Oxalate crystals in

ovary wall

+ + + – –

Ovary syncarpous + – – + +

Stigma shape Restricted to

carpel tip

Restricted to

carpel tip

Restricted to

carpel tip

Decurrent Decurrent

Bundles per carpel 3 5 3–5 3 5

Dorsal bundles Not reaching

style

? Reaching stigma Reaching

stigma

Reaching stigma

Secretory hairs in

ovary

+ – – –a –

Ovules two per

carpel and

superposed

+ + +/– + –

Ovules bitegmic +/– + (–) + + +

Ovule structure Hemianatropous Hemianatropous Ortho-,

hemianatropous

Anatropous Anatropous

Anthers

disporangiate

+ +/– – – –

Endothecium One-layered ? One-layered One-two-

layered

One-layered

Presence of

endoapertures

+ +/– – + –

Data from Endress (1995), Endress and Stumpf (1990, 1991), Endress and Igersheim (1999), Furness et al.

(2007), Nast and Bailey (1945), von Balthazar and Endress (2002), Wang et al. (2006), and this studya Pachysandra has non-secretory hairs at the transition of the ventral slit and the placenta (Endress and Igersheim

1999)


Proteaceae (Endress and Igersheim 1999). Pollen

grains are of a generalized type (tricolporate,

subprolate and reticulate, with endoapertures:

Erdtman 1952; Furness et al. 2007). Sabiaceae

share endoapertures only with two other fami-

lies of early-diverging eudicots, Buxaceae and

Menispermaceae. Recent molecular evidence

(Worberg et al. 2007) supports the monophyly

of Sabiaceae and places the family as the second

branch in the basal eudicot grade with inconclu-

sive support. This places the family in an isolated

position in relation to the other early diverging

eudicots as might be expected from the unusual

floral morphology which evolved clearly sepa-

rately with little evidence of a close association

with other families (Wanntorp and Ronse De

Craene 2007).

We thank Frieda Christie and Dr. Chris Jeffree for

assistance with the SEM. We are also grateful to Dr.

Toru Tokuoka for collecting flower buds of Meliosmapinnata. Travel for LW to RBGE was possible

through SYNTHESYS grant GB-TAF 1626. Helpful

comments by Dmitry Sokoloff and an anonymous

reviewer are gratefully acknowledged.

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Morphology and Anatomy of the Flower of Meliosma (Sabiaceae)- Implications for Pollination

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