Floral structure of Emmotum (Icacinaceae sensu stricto or Emmotaceae), a phylogenetically isolated genus of lamiids with a unique pseudotrimerous gynoecium,bitegmic ovules and monosporangiate thecae

Background and Aims

Icacinaceae sensu stricto consist of a group of early branching lineages of lamiids whose relationships are not yet resolved and whose detailed floral morphology is poorly known. The most bizarre flowers occur in Emmotum: the gynoecium has three locules on one side and none on the other. It has been interpreted as consisting of three fertile and two sterile carpels or of one fertile carpel with two longitudinal septa and two sterile carpels. This study focused primarily on the outer and inner morphology of the gynoecium to resolve its disputed structure, and ovule structure was also studied. In addition, the perianth and androecium were investigated.

Methods

Flowers and floral buds of two Emmotum species, E. harleyi and E. nitens, were collected and fixed in the field, and then studied by scanning electron microscopy. Microtome section series were used to reconstruct their morphology.

Key Results

The gynoecium in Emmotum was confirmed as pentamerous, consisting of three fertile and two sterile carpels. Each of the three locules behaves as the single locule in other Icacinaceae, with the placenta of the two ovules being identical, which shows that three fertile carpels are present. In addition, it was found that the ovules are bitegmic, which is almost unique in lamiids, and that the stamens have monosporangiate thecae, which also occurs in the closely related family Oncothecaceae, but is not known from any other Icacinaceae sensu lato so far.

Conclusions

The flowers of Emmotum have unique characters at different evolutionary levels: the pseudotrimerous gynoecium at angiosperm level, the bitegmic ovules at lamiid level and the monosporangiate thecae at family or family group level. However, in general, the floral morphology of Emmotum fits well in Icacinaceae. More comparative research on flower structure is necessary in Icacinaceae and other early branching lineages of lamiids to better understand the initial evolution of this large lineage of asterids.     

Gynoecium evolution in angiosperms: Monomery,pseudomonomery, and mixomery

The presence of a gynoecium composed of carpels is a key feature of angiosperms. The carpel is often regarded as a homologue of the gymnosperm megasporophyll (that is, an ovule-bearing leaf), but higher complexity of the morphological nature of carpel cannot be ruled out. Angiosperm carpels can fuse to form a syncarpous gynoecium. A syncarpous gynoecium usually includes a well-developed compitum, an area where the pollen tube transmitting tracts of individual carpels unite to enable the transition of pollen tubes from one carpel to another. This phenomenon is a precondition to the emergence of carpel dimorphism manifested as the absence of a functional stigma or fertile ovules in part of the carpels. Pseudomonomery, which is characterized by the presence of a fertile ovule (or ovules) in one carpel only, is a specific case of carpel dimorphism. A pseudomonomerous gynoecium usually has a single plane of symmetry and is likely to share certain features of the regulation of morphogenesis with the monosymmetric perianth and androecium. A genuine monomerous gynoecium consists of a single carpel. Syncarpous gynoecia can be abruptly transformed into monomerous gynoecia in the course of evolution or undergo sterilization and gradual reduction of some carpels. Partial or nearly complete loss of carpel individuality that precludes the assignment of an ovule (or ovules) to an individual carpel is observed in a specific group of gynoecia. We termed this phenomenon mixomery, since it should be distinguished from pseudomonomery.     

The Carpel of Moringa

The gynoecium of Moringa is tricarpellary, syncarpous and unilocularwith parietal placentation. The three carpel primordia ariseindependently but soon become connected resulting in an annularstructure which develops into the tubular gynoecium. The gynoeciumis supplied with three dorsal and three marginal bundles. Thelatter represent the fusion product of the marginal bundlesof adjacent carpels and each splits into three in the ovarywall. The ovules receive their vascular supply from a commonbundle, which branches from the dorsal trace of the carpel atthe base of the ovary. The derivation of the gynoecium fromconduplicate carpels is postulated. Moringa oleifera, carpel morphology, conduplicate carpel, carpel ontogeny     

Morphology of the gynoecium and systematic position of the Ochnaceae

The gynoecium is syncarpous in all Ochnaceae. In the Ochnoideae carpels are peltate with a conventional cross-zone bearing one ovule, or, in Lophira , a very broad cross-zone with an horizontal ovular row. In Ochna and Brackenridgea , the style is gynobasic, each carpel develops transmitting tissue on its morphologically dorsal surface, and this tissue lines a canal or originates a solid inner strand in each carpel at style level. The style is tubular, with an inner cuticle, and compound, each component with its own transmitting tissue. In Ouratea the style is solid with a single compound transmitting strand. In Lophira and Elvasia the transmitting tissue seems to be developed by the morphologically ventral carpellary surfaces. Ovules are unitegmic with a bivalent integument.
In the Sauvagesioideae carpels are peltate, but with ovules above the cross-zones, on margins of the symplicate zone. In Euthemis , there is one ovule on each side of, and close to, each cross-zone. The single stylar canal is bounded by the morphologically dorsal carpellary surfaces. In Sauvagesia ovules occur on both sides of the cross-zones but most of them are above on carpel margins, as are all ovules of Cespedesia. The stylar canal of Sauvagesia is bounded by the ventral carpel surfaces, three strips of the outer surface passing inside at the sutures and developing into transmitting tissue. The stylar canal of Cespedesia is bounded by the dorsal carpel surfaces. The gynoecium of Wallacea has two epeltate carpels with a laminar placentation, the carpel margins being displaced on to the topographically ventral carpel surfaces with a row of ovules along each margin. Ovules are bitegmic.
The Ochnoideae, which shows relationships with the Rutaceae, Meliaceae, Simaroubaceae and Hippocastanaceae, is more advanced than the Sauvagesioideae, which clearly belongs in the Violales. The Ochnaceae is to be placed in the Violales.     

A TEST OF SEVERAL HYPOTHESES FOR THE DETERMINATION OF SEED NUMBER IN AMELANCHIER ARBOREA,USING SIMULATED PROBABILITY DISTRIBUTIONS TO EVALUATE DATA

The number of seeds per fruit is variable within Amelanchier arborea trees. Because A. arborea flowers are five-carpellate and each carpel contains two ovules, we were able to use the pattern of seed maturation within fruits to test whether the failure of some ovules to develop into seeds is determined by mechanisms operating at the level of carpels, such as stigma-clogging, or by mechanisms operating at the level of ovules, such as ovule infertility. The presence of one-, two-, and zero-seeded carpels demonstrated that the number of ovules developing into seeds was not due entirely to carpel-level phenomena. In order to test the hypothesis of carpel independent seed development, without the assumption that all ovules have the same probability of developing into seeds, it was necessary to use simulation, since no conventional statistical models were appropriate. Analysis of this simulation allowed us to reject carpel independent processes as the only determinant of seed number. A mixed model of seed development, in which some carpels fail entirely and ovules in the remaining carpels develop equiprobably, was shown to be consistent with the data.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE VII. POMOIDEAE: CHAENOMELES,CYDONIA, DOCYNIA

The multi-ovulate pomoids, Chaenomeles, Cydonia, and Docynia, all have closed sutures and extensive fusion between carpel and floral cup and between ovular and wing bundles. Although the ovules in Docynia are generally apotropic and few in number (4–7), the ovules in the other two genera are pleurotropic and numerous (15–48). A statistical treatment of the whole tribe of Pomoideae shows that in carpels with open sutures ovular and wing bundles definitely tend to be separate while in those with closed sutures these bundles tend to be fused. To a lesser degree carpels with open sutures also tend to have bitegmic ovules, separate carpels, and a lesser extent of fusion between carpel and floral cup, while carpels with closed sutures tend to have monotegmic ovules, united carpels, and a greater extent of fusion between carpel and floral cup.     

Floral Ontogenetic Evidence in Support of the Willdenowia Clade of South African Restionaceae

Willdenowia clade of Restionaceae was studied to understand patterns of reduction of floral elements and sample evidence for discussing the relationships of the group. All species studied are characterized by a concordant reductive trend involving the retardation/reduction of the perianth, the loss of the anterior carpel and the displacement of the remaining carpels, linked with a strongly compressed spikelet. Different modes of carpel reduction, such as a progressive or immediate loss, or fusion of two neighboring carpels, are presented and discussed. The most parsimonious event of gynoecium evolution for the Willdenowia clade is either the sterilization of two carpels in an originally trimerous gynoecium, followed by the loss of the anterior carpel, or the sudden loss of the anterior carpel, preceeding the sterilization of one lateral carpel. The concordant development of the taxa of the Willdenowia clade supports a one-time loss of a carpel and the homogeneity of the clade. Received 12 March 2001/ Accepted in revised form 29 May 2001     

Contributions to the systematic position of Hydrolea (Hydroleaceae) based on floral development

In the flower of Hydrolea palustris, unusually orientated with one sepal abaxially, organogenesis starts in following sequence: five sepals (2/5 sequence), five simultaneously initiated alternating petals, five episepalous stamens, two (seldom three) carpels forming a coenocarpous septate gynoecium. The two carpels are orientated rather in the diagonal floral plane than in the median one. Petal primordia fuse very late by forming interprimordial bridges (late sympetaly!). Many ovules develop on considerably widened placentas. On the very basis of the superior ovary a five-humped nectary disk is formed.Within Solanales (APG II 2003) late sympetaly, an intrastaminal disk and a 2-carpellate, septate, superior ovary are found in Hydroleaceae, Convolvulaceae, and Solanaceae. Enlarged axile placentas characterize Hydrolea, Solanaceae, and Sphenocleaceae but Sphenocleaceae differ considerably by early sympetaly. Montiniaceae differ by having a choripetalous corolla. Nearly diagonal orientation of the carpels seems to relate Hydrolea close to Solanaceae, but the orientation of the calyx is different.     

臭椿花器官分化的初步研究

利用扫描电镜(SEM)和光镜(LM)对臭椿花序及花器官的分化和发育进行了初步研究,表明:1)臭椿花器官分化于当年的4月初,为圆锥花序;2)分化顺序为花萼原基、花冠原基、雄蕊原基和雌蕊原基。5个萼片原基的发生不同步,并且呈螺旋状发生;5个花瓣原基几乎同步发生且其生长要比雄蕊原基缓慢;雄蕊10枚,两轮排列,每轮5个原基的分化基本是同步的;雌蕊5,其分化速度较快;3)在两性花植株中,5个心皮顶端粘合形成柱头和花柱,而在雄株中,5个心皮退化,只有雄蕊原基分化出花药和花丝。本研究着重观察了臭椿中雄花及两性花发育的过程中两性花向单性花的转变。结果表明,臭椿两性花及单性花的形成在花器官的各原基上是一致的(尽管时间上有差异),雌雄蕊原基同时出现在每一个花器官分化过程中,但是,可育性结构部分的形成取决于其原基是否分化成所应有的结构:雄蕊原基分化形成花药与花丝,雌蕊原基分化形成花柱、柱头和子房。臭椿单性花的形成是由于两性花中雌蕊原基的退化所造成,其机理有待于进一步研究。     

Comparative floral structure and systematics in Crossosomatales (Crossosomataceae, Stachyuraceae, Staphyleaceae, Aphloiaceae, Geissolomataceae, Ixerbaceae, Strasburgeriaceae)

Floral structure of all putative families of Crossosomatales as suggested by molecular studies was comparatively studied. The seven comprise Crossosomataceae, Stachyuraceae, Staphyleaceae, Aphloiaceae, Geissolomataceae, Ixerbaceae, and Strasburgeriaceae. The entire clade (1) is highly supported by floral structure, also the clades (in sequence of diminishing structural support): Ixerbaceae/Strasburgeriaceae (2), Geissolomataceae/Ixerbaceae/Strasburgeriaceae (3), Aphloiaceae/Geissolomataceae/Ixerbaceae/Strasburgeriaceae (4), and Crossosomataceae/Stachyuraceae/Staphyleaceae (5). Among the prominent floral features of Crossosomatales (1) are solitary flowers, presence of a floral cup, imbricate sepals with outermost smaller than inner, pollen grains with horizontally extended endoapertures, shortly stalked gynoecium, postgenitally united carpel tips forming a compitum, stigmatic papillae two‐ or more‐cellular, ovary locules tapering upwards, long integuments forming zigzag micropyles, cell clusters with bundles of long yellow crystals, mucilage cells, seeds with smooth, sclerified testa and without a differentiated tegmen. Clade (2) is characterized by large flowers, petals forming a tight, pointed cone in bud, stamens with long, stout filaments and sagittate anthers, streamlined, conical gynoecium, antitropous ovules, rudimentary aril, lignified, unicellular, T‐shaped hairs and idioblasts with striate mucilaginous cell walls. Clade (3) is characterized by alternisepalous carpels, punctiform stigma formed by postgenitally united and twisted carpel tips, synascidiate ovary, only one or two pendant ovules per carpel, nectary recesses between androecium and gynoecium. Clade (4) is characterized by pronounced ‘pollen buds’. Clade (5) is characterized by polygamous or functionally unisexual flowers, x‐shaped anthers, free and follicular carpels (not in Stachyuraceae). Crossosomataceae and Aphloiaceae, although not retrieved as a clade in molecular studies, share several special floral features: polystemonous androecium; basifixed anthers without a connective protrusion; stigma with two more or less decurrent crests; camplyotropous ovules and reniform seeds; simple, disc‐shaped nectaries and absence of hairs. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 147 , 1–46.     

Patterns of angiospermy development before carpel sealing across living angiosperms: diversity,and morphological and systematic aspects

Almost all angiosperms are angiospermous, i.e. the ovules are enclosed in carpels at anthesis and during seed development, but angiospermy develops in different ways across angiosperms. The most common means of carpel closure is by a longitudinal ventral slit in carpels that are partly or completely free. In such carpels, the closure process commonly begins at midlength of the prospective longitudinal slit and then proceeds downward and upward. Closure by a transverse slit is rarer, but it is prominent in groups of the ANITA grade and in a few early branching monocots (some Alismatales) and some early branching eudicots (a few Ranunculaceae and Nelumbonaceae), in these eudicots combined with a more or less developed longitudinal slit. In all these cases the carpels have a single ovule in ventral median position. In ANITA lines with pluriovulate carpels, there is only a short longitudinal slit in the uniformly ascidiate carpels. In carpels with a unifacial style the closure area is narrow; this pattern is rare and scattered mainly in some wind‐pollinated monocots and eudicots. In most angiosperms the carpels become closed before the ovules are visible from the outside of the still incompletely closed carpels (early carpel closure). This is notably the case in the ANITA grade and magnoliids. Delayed carpel closure, with the ovules visible before the carpels are closed, is much rarer and is concentrated in a few monocots (mainly some Alismatales and some Poales) and a few eudicots (mainly a few Ranunculales and many Caryophyllales, and scattered in some other eudicots). A kind of delayed carpel closure (with the placenta visible before closure but mostly not the ovules) also occurs in syncarpous gynoecia with a free central placenta. Most gynoecia with a free central placenta occur in the superasterids. In such gynoecia the individual carpel tips are not differentiated but the opening in young gynoecia has the shape of a circular diaphragm. In this case, when ovary septa and free carpel tips are missing, the number of carpels is sometimes unclear (Primulaceae, Lentibulariaceae, some Santalaceae). Extremely ascidiate carpels are concentrated in the ANITA grade, a few magnoliids and some early branching monocots. Aspects of potential advantages of plicate vs. ascidiate carpels with regard to flexibility of pollen tube transmitting tract differentiation are discussed. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 556–591.     

Gynoecium diversity and systematics of the basal eudicots

Gynoecium and ovule structure was compared in representatives of the basal eudicots, including Ranunculales (Berberidaceae, Circaeasteraceae, Eupteleaceae, Lardizabalaceae, Menispermaceae, Papaveraceae, Ranunculaceae), Proteales (Nelumbonaceae, Platanaceae, Proteaceae), some families of the former ‘lower’ hamamelids that have been moved to Saxifragales (Altingiaceae, Cercidiphyllaceae, Daphniphyllaceae, Hamamelidaceae), and some families of uncertain position (Gunneraceae, Myrothamnaceae, Buxaceae, Sabiaceae, Trochodendraceae). In all representatives studied, the carpels (or syncarpous gynoecia) are closed at anthesis. This closure is attained in different ways: (1) by secretion without postgenital fusion (Berberidaceae, Papaveraceae, Nelumbonaceae, probably Circaeaster); (2) by a combination of postgenital fusion and secretion; (2a) with a complete secretory canal and partly postgenitally fused periphery (Lardizabalaceae, Menispermaceae, some Ranunculaceae, Sabiaceae); (2b) with an incomplete secretory canal and completely fused periphery (Tro-chodendron); (3) by complete postgenital fusion without a secretory canal (most Ranunculaceae, Eupteleaceae, Platanaceae, Proteaceae, all families of Saxifragales and incertae sedis studied here). Stigmas are double-crested and decurrent in most of the non-ranunculalian taxa; unicellular-papillate in most taxa, but with multicellular protuberances in Daphniphyllaceae and Hamamelidaceae. Carpels predominantly have three vascular bundles, but five in Proteales (without Nelumbonaceae), Myrothamnaceae and Trochodendraceae. The latter two also share ‘oil’ cells in the carpels. Stomata on the outer carpel surface are present in the majority of Ranunculales and Proteales, but tend to be lacking in the saxifragalian families. In basal eudicots, especially in the non-ranunculalian families there is a trend to form more than one ovule per carpel but to develop only one seed, likewise there is a trend to have immature ovules at anthesis. Ovule number per carpel is predominantly one or two. Proteales (without Nelumbonales) mainly have orthotropous ovules, the other groups have anatropous (or hemitropous or campylotropous) ovules. The outer integument is annular in the groups with orthotropous or hemitropous ovules, and also in a number of saxifragalian families with anatropous ovules. In Proteales the integuments are predominantly lobed but there is no distinct pattern in this feature among the other groups. Among Ranunculales two pairs of families (Lardizabalaceae/Menispermaceae and Bcrberidaceae/Papaveraceae) due to similarities in gynoecium structure can be recognized, which are not apparent in molecular analyses. The close relationship of Platanaceae and Proteaceae is supported by gynoecium structure but gynoecial features do not support their affinity to Nelumbonaceae. The alliance of Daphniphyllaceae with Hamamelidaceae s.l. is also supported.     

Floral development of Cardiopteris,with emphasis on gynoecial structure and ovular morphology

Cardiopteris is unique in the expanded Cardiopteridaceae for several distinctive features, including its gynoecial structure and ovular morphology. We studied the floral development of Cardiopteris to clarify floral morphology and document floral development. Cardiopteris has three carpel primordia, which are separate at their tips but congenitally fused at their bases. The synascidiate zone (the fused proximal part) develops into the unilocular ovary; the three discrete carpel apices diverge in development: the apex of the adaxial carpel differentiates into a style and stigma, while the apices of the two lateral-abaxial carpels elongate and develop into a fleshy appendage only after fertilization. The ovules are attached to the lateral-abaxial carpels. At anthesis, the ovules are ategmic and orthotropous without funicles (morphologically undifferentiated). Functional differentiation occurs in the three carpels of Cardiopteris: the adaxial one is the site of pollination, while the lateral-abaxial two produce ovules. The ategmic orthotropous ovule is unusual in Cardiopteridaceae and is an apomorphy of Cardiopteris.     

Zur Entwicklung des Gynoeceums beiBergenia cordifolia (Saxifragaceae)

Scanning electron microscopical investigations of flower buds of the perennial herbBergenia cordifolia (Haw.)A. Br. (Saxifragaceae) reveal a primitive gynoecium. During ontogenesis the margins of the carpel lamina transgress on the apical cone of the axis by meristem incorporation and finally fuse with the margins of the opposite carpel. These processes of meristem incorporation and fusion first lead to gamophylly and furthermore to carpel peltation, as is demonstrated by SEM-photographs (ring-shaped dike and common septum of the two carpels). As a result of carpel peltation, the lowest point of the septum deliminates the synascidiate zone. Above this point, the symplicate and, eventually, the plicate zone follows (vid. ventral suture). The margins of the carpel lamina merely touch each other without being coalesced. The preparation of a window in the carpel's dorsal side permits a look at a massive lateral placenta (Leinfellner 1951) developing the ovules. In the lower third—in lateral position at the placenta's margin—the first ovules are seen, the next ones follow in acropetal and basipetal direction, as well as to the periphery of the placenta.

     

VARIATION IN STRUCTURE AMONG FRUITS OF MALOIDEAE (ROSACEAE)

Fruits of Rosaceae subfamily Maloideae are known as pomes, a fruit type unique to the Maloideae. Using light microscopy we examined the pomes of 173 species, broadly representing the taxonomic diversity of the subfamily. Significant variation occurs among pomes in retention, orientation, and texture of calyx lobes on the distal end of the fruit; density and distribution of sclereids in the flesh; heterogeneity among flesh parenchyma cells; carpel number and number of ovules per carpel; degree of connation among the carpels and adnation between ovary and hypanthium; and texture of the core. Phenetic clustering closely links congeneric fruits. Sorbus is a notable exception; fruits of the compound-leaved species form a cluster unrelated to fruits of the simple-leaved species. Fruits of Malus are also heteromorphic. Division of the Maloideae into two tribes, Crataegeae and Sorbeae, based largely on texture of the core is not substantiated. We hypothesize that the ancestral pome had five carpels, minimal connation of carpels, minimal adnation of ovaries to the hypanthium, two ovules per carpel, and a leathery core. Various adaptations for frugivore dispersal of the seeds partially explain trends in pome evolution.     

Regulation of gynoecium marginal tissue formation by LEUNIG and AINTEGUMENTA

The carpel is the female reproductive organ of flowering plants. In Arabidopsis, congenital fusion of two carpels leads to the formation of an enclosed gynoecium. The margins of the two fused carpels are meristematic in nature and give rise to placentas, ovules, septa, abaxial repla, and the majority of the stylar and stigmatic tissues. Thus, understanding how the marginal tissues are specified and identifying genes that direct their development may provide important insight into higher plant reproductive development. In this study, we show that LEUNIG and AINTEGUMENTA are two critical regulators of marginal tissue development. Double mutants of leunig aintegumenta fail to develop placentas, ovules, septa, stigma, and style. This effect is specific to the leunig aintegumenta double mutant and is not found in other double mutant combinations such as leunig apetala2 or aintegumenta apetala2. Additional analyses indicate that the absence of marginal tissues in leunig aintegumenta double mutants is not mediated by ectopic AGAMOUS. We propose that LEUNIG and AINTEGUMENTA act together to control the expression of common target genes that regulate cell proliferation associated with marginal tissue development.     

Intercarpellary growth of pollen tubes in the extragynoecial compitum and its contribution to fruit set in an apocarpous species, Schisandra sphenanthera (Schisandraceae)

? Premise of the study: Apocarpous plants possess carpels that are separated in the gynoecium. Extragynoecial compita, commonly occurring in basal angiosperms, have been proposed to have the potential to increase offspring quantity in apocarpous species through the intercarpellary growth of pollen tubes. To date, the impact of an extragynoecial compitum on fruit or seed set has not been studied in any species. This study investigated the pollen tube pathway between adjacent carpels and its contribution to fruit set in Schisandra sphenanthera. ? Methods: We investigated the fruit set ratio in the field and collected hundreds of gynoecia at their full flowering stage. Pollinated carpel ratio and pollen tube pathway observations were performed using fluorescence optics. ? Key results: Pollen grains germinated and tubes extended along the pseudostyle surface. Some of them turned and entered the ovules at the end of the stigmatic crest, whereas others subsequently grew into neighboring carpels through promontory connections located at the base of the unfused carpels. No tubes were found growing on the surface of the receptacle. More than 24 carpels could be fertilized by pollen tubes from one carpel through hand pollination. The pollinated carpel ratio was significantly lower than the fruit set ratio under natural conditions. ? Conclusions: Pollen tubes from one carpel can easily cross in the extragynoecial compitum between the adjacent carpels of S. sphenanthera, and this intercarpellary growth of pollen tubes can significantly increase the fruit set of apocarpous species, at least in S. sphenanthera.     

GYNOECIAL ONTOGENY AND MORPHOLOGY,AND POLLEN TUBE PATHWAY IN BLACK MAPLE,ACER SACCHARUM SSP. NIGRUM (ACERACEAE)

The black maple (Acer saccharum Marsh, ssp. nigrum [Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid- to late-summer, as two separate, opposite, hood-shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.