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.     

The unusual gynoecium structure and extragynoecial pollen-tube pathway in <Emphasis Type="Italic">Phytolacca</Emphasis> (Phytolaccaceae)

The fusion of carpels into a unified compound gynoecium is considered a dominant feature of angiosperm evolution and it also occurs by postgenital fusion during the gynoecium development in some apocarpous species. However, we found the reverse process, the separation of carpels from combined carpel primordia, during the development of the gynoecium in Phytolacca. Semithin sectioning and scanning electron microscopy were utilised to observe the structure and development of the gynoecia in Phytolacca acinosa and Phytolacca americana, fluorescence microscopy was utilised to observe the pollen tube growth in the gynoecia of the two species, and the topology method was applied to analyze the relationship between the gynoecium structure and pollen tube pathway. Although the gynoecia of P. acinosa and P. americana are both syncarpous, the degree of carpel fusion in the mature gynoecia of the two syncarpous species is different as a result of variant developmental processes. However, change in the degree of carpel fusion during the development of gynoecia in Phytolacca does not affect pollen tube growth because of the existence of the extragynoecial pollen-tube pathway. Thus, the change in the degree of carpel fusion in Phytolacca is primarily the result of diversification of developmental processes related to selection pressure.     

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.     

Multicarpellate gynoecia in angiosperms: occurrence,development, organization and architectural constraints

Most angiosperms have gynoecia with two to five carpels. However, more than five carpels (here termed ‘multicarpellate condition’) are present in some representatives of all larger subclades of angiosperms. In such multicarpellate gynoecia, the carpels are in either one or more than one whorl (or series). I focus especially on gynoecia in which the carpels are in a single whorl (or series). In such multicarpellate syncarpous gynoecia, the closure in the centre of the gynoecium is imprecise as a result of slightly irregular development of the carpel flanks. Irregular bumps appear to stuff the remaining holes. In multicarpellate gynoecia, the centre of the remaining floral apex is not involved in carpel morphogenesis, so that this unspent part of the floral apex remains morphologically undifferentiated. It usually becomes enclosed within the gynoecium, but, in some cases, remains exposed and may or may not form simple excrescences. The area within the remaining floral apex is histologically characterized by a parenchyma of simple longitudinal cell rows. In highly multicarpellate gynoecia with the carpels in a whorl, the whorl tends to be deformed into an H‐shaped or star‐shaped structure by differential growth of the floral sectors, so that carpels become aligned in parallel rows, in which they face each other with the ventral sides. In this way, a fractionated compitum may still be functional. Multicarpellate gynoecia (with the carpels in one whorl or series) occur in at least one species in 37 of the 63 angiosperm orders. In contrast, non‐multicarpellate gynoecia are present in at least one species of all 63 orders. The basal condition in angiosperms is more likely non‐multicarpellate. Multicarpellate gynoecia are restricted to flowers that are not highly synorganized. In groups with synorganized androecium and gynoecium and in groups with elaborate monosymmetric flowers, multicarpellate gynoecia are lacking. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 1–43.     

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     

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.     

Floral development in <Emphasis Type="Italic">Thermopsis turcica</Emphasis>, an unusual multicarpellate papilionoid legume

The vast majority of the species of family Leguminosae have an apocarpous monomerous gynoecium. However, only a few taxa regularly produce multicarpellate gynoecia. The only known species of papilionoid legumes which has both a typical “flag blossom” and more than one carpel is Thermopsis turcica (tribe Thermopsideae). We studied the floral ontogeny of T. turcica with special reference to its gynoecium initiation and development. Flowers arise in simple terminal racemes in a helical order and are subtended by bracts. Bracteoles are initiated but then suppressed. Sepals appear more or less simultaneously. Then, petals emerge and remain retarded in development until later stages. The gynoecium usually includes three carpels with an abaxial one initiating first and two adaxial carpels arising later and developing somewhat asynchronously. The abaxial carpel appears concomitant with the outer stamens and is always oriented with its cleft toward the adaxial side, while the adaxial carpels face each other with their clefts and have them slightly turned to the adaxial side. Rarely uni-, bi- or tetracarpellate flowers arise. Seed productivity of T. turcica is on approximately the same level as in unicarpellate species of Thermopsis hence supporting the fact that the multicarpellate habit is adaptive or at least not harmful in this species.     

Unique growth paths of heterospecific pollen tubes result in late entry into ovules in the gynoecium of Sagittaria (Alismataceae)

• Pollen‐pistil interactions are a fundamental process in the reproductive biology of angiosperms and play a particularly important role in maintaining incipient species that exist in sympatry. However, the majority of previous studies have focused on species with syncarpous gynoecia (fused carpels) and not those with apocarpous gynoecia (unfused carpels).
• In the present study, we investigated the growth of conspecific pollen tubes compared to heterospecific pollen tubes in Sagittaria species, which have apocarpous gynoecia. We conducted controlled pollinations between S. pygmaea and S. trifolia and observed the growth of conspecific and heterospecific pollen tubes under a fluorescence microscope.
• Heterospecific and conspecific pollen tubes arrived at locules within the ovaries near simultaneously. However, conspecific pollen tubes entered into the ovules directly, whereas heterospecific tubes passed through the carpel base and adjacent receptacle tissue, to ultimately fertilize other unfertilized ovules. This longer route taken by heterospecific pollen tubes therefore caused a delay in the time required to enter into the ovules. Furthermore, heterospecific pollen tubes displayed similar growth patterns at early and peak pollination. The growth pattern of heterospecific pollen tubes at late pollination was similar to that of conspecific pollen tubes at peak pollination.
• Heterospecific and conspecific pollen tubes took different routes to fertilize ovules. A delayed entry of heterospecific pollen into ovules may be a novel mechanism of conspecific pollen advantage (CPA) for apocarpous species.

     

Comparative floral structure and systematics in Celastrales (Celastraceae, Parnassiaceae, Lepidobotryaceae)

Floral morphology, anatomy and histology in the newly circumscribed order Celastrales, comprising Celastraceae, Parnassiaceae and Lepidobotryaceae are studied comparatively. Several genera of Celastraceae and Lepidobotrys (Lepidobotryaceae) were studied for the first time in this respect. Celastraceae are well supported as a group by floral structure (including genera that were in separate families in earlier classifications); they have dorsally bulged‐up locules (and thus apical septa) and contain oxalate druses in their floral tissues. The group of Celastraceae and Parnassiaceae is also well supported. They share completely syncarpous gynoecia with commissural stigmatic lobes (and strong concomitant development of the commissural vascular bundles but weak median carpel bundles), only weakly crassinucellar or incompletely tenuinucellar ovules with an endothelium, partly fringed sepals and petals, protandry in bisexual flowers combined with herkogamy by the movement of stamens and anther abscission, and stamens fused with the ovary. In contrast, Lepidobotryaceae are more distant from the other two families, sharing only a handful of features with Celastraceae (not Parnassiaceae), such as pseudohermaphroditic flowers, united stamen bases forming a collar around the gynoecium and seeds with a conspicuous aril. However, all three families together are also somewhat supported as a group and share petals that are not retarded in late floral bud development, 3‐carpellate gynoecia, ventral slits of carpels closed by long interlocking epidermal cells and pollen tube transmitting tissue encompassing several cell layers, both integuments usually more than two cell layers thick, and only weak or lacking floral indumentum. In some molecular analyses Celastrales form an unsupported clade with Malpighiales and Oxalidales. This association is supported by floral structure, especially between Celastrales and Malpighiales. Among Celastrales, Lepidobotryaceae especially share special features with Malpighiales, including a diplostemonous androecium with ten fertile stamens, epitropous ovules with an obturator and strong vascularization around the chalaza. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 149 , 129–194.     

Convergent elaboration of apocarpous gynoecia in higher advanced dicotyledons (Sapindales, Malvales, Gentianales)

The apocarpous gynoecia of three separate groups of higher advanced dicotyledons show postgenital fusion of their apical parts. In this fused region the pollen tube transmitting tissue of the carpels is united into a compitum, which provides advantages of a syncarpous to the apocarpous gynoecium. It is supposed that in at least some of these groups the general evolutionary trend of the angiosperms from apocarpy towards syncarpy is reversed.     

Pollen tubes enter neighbouring ovules by way of receptacle tissue,resulting in increased fruit-set in Sagittaria potamogetifolia Merr

Using fluorescence microscopy, deposition of pollen on stigmas and pollen tube growth in the gynoecium of Sagittaria potamogetifolia Merr., a monoecious species with an apocarpous gynoecium, were observed. The maximum rate of pollination averaged 83.9 +/- 4.7 %, and the number of pollen grains per stigma ranged from zero to 30. Pollen tubes grew through one stigma to the base of the ovary at almost the same speed, but generally only one of the pollen tubes then turned towards the ovule and finally entered the nucellus through the micropyle. The other pollen tubes grew through the ovary base and the receptacle tissue into ovules of adjacent carpels whose stigmas were not pollinated or which had been pollinated later. This phenomenon is termed pollen tube 'reallocation' by the authors. To verify the direct effect of the phenomenon on fruit set, artificial pollination experiments were conducted in which two or more pollen grains were placed onto only one stigma in each gynoecium; frequently more than one fruitlet was obtained from each flower treated. The reallocation of pollen tubes among pistils in the gynoecium could effect fertilization of ovules of unpollinated pistils and lead to an increase in sexual reproduction efficiency. It would, to some extent, also increase pollen tube competition among pistils of the whole gynoecium.     

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.     

Morphology and development of the female flowers in Geonoma interrupta (Arecaceae)

Morphology and development of the female flowers in Geonoma interrupta are described and compared with other taxa within Arecaceae. Inflorescences are pleiothyrses. Cincinni are immersed in pits and arranged according to the Fibonacci pattern along the rachillae. The gynoecium is composed of three free carpels in early stages and later becomes pseudomonomerous. Two carpels are sterile; they develop to different degrees and are commonly unequal in size. The fertile carpel contains a single, crassinucellate, anatropous ovule. Styles are formed in each carpel. The style of the fertile carpel becomes basifixed as the ovary enlarges. The stigmas remain free and plicate during development and expose unicellular papillae at anthesis. Pollen tube transmitting tracts and a compitum are present in the ventral slits of the stigmas and the postgenitally united styles during anthesis. A septal nectary is formed by incomplete union of the flanks of the carpels at the base of the gynoecium, and nectar is secreted from an epithelium. It is suggested that in Geonoma as a whole, the attraction of pollinators to female flowers is due to a combination of nectar reward and partial mimicry of male flowers.     

Comparative floral structure and systematics of Pelagodoxa and Sommieria (Arecaceae)

Floral structure is compared in Pelagodoxa and Sommieria (Arecaceae, Arecoideae). Male flowers have three free, imbricate sepals, three basally congenitally united and apically valvate petals, and six stamens. Anthers are dorsifixed and dehiscence introrse. The sterile gynoecium is tricarpellate. Female flowers have three free, imbricate sepals and three free, imbricate petals, which are slightly fused with the sepals at the base. Four to six staminodes are congenitally united at the base and fused with the ovary for a short distance. The gynoecium is syncarpous. Carpels are almost equal in early development; later the gynoecium becomes pseudomonomerous. The three stigmatic branches are equally developed, apical and sessile. The carpels are (syn-)ascidiate up to the level of the placenta and (sym-)plicate above. Each carpel has one ovule, in the sterile carpels it is aborted at anthesis. The fertile ovule is erect up to anthesis and pendant afterwards because of the bulging out of the ovary. Pollen tube transmitting tracts (PTTT) encompass the secretory epidermis of the ventral slits of each carpel. Floral structure in Pelagodoxa and Sommieria supports the sister group relationship between the two genera suggested in recent molecular phylogenies and reflects their close relationships to a major clade of pseudomonomerous arecoid palms from the Indo-Pacific region.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 27–39.     

Comparative floral morphology and anatomy of Anacardiaceae and Burseraceae (Sapindales), with a special focus on gynoecium structure and evolution

Anacardiaceae and Burseraceae are traditionally distinguished by the number of ovules (1 vs. 2) per locule and the direction of ovule curvature (syntropous vs. antitropous). Recent molecular phylogenetic studies have shown that these families are sister groups in Sapindales after having been separated in different orders for a long time. We present a comparative morphological study of the flower structure in both families. The major clades, usually supported in molecular phylogenetic analyses, are well supported by floral structure. In Anacardiaceae, there is a tendency to gynoecium reduction to a single fertile carpel (particularly in Anacardioideae). The single ovule has a long and unusually differentiated funicle, which connects with the stylar pollen tube transmitting tract in all representatives studied. In Anacardiaceae–Spondiadoideae, there is a tendency to form an extensive synascidiate zone, with a massive remnant of the floral apex in the centre; these features are also present in Beiselia (Burseraceae) and Kirkiaceae (sister to Anacardiaceae plus Burseraceae) and may represent a synapomorphy or apomorphic tendency for the three families. In core Burseraceae, gynoecium structure is much less diverse than in Anacardiaceae and has probably retained more plesiomorphies. Differences in proportions of parts of the ovules in Anacardiaceae and Burseraceae are linked with the different direction of ovule curvature. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 499–571.     

False paracarpy in Seemannaralia (Araliaceae): from bilocular ovary to unilocular fruit

Background and Aims

Seemannaralia appears to be fundamentally different from all other Araliaceae in the presence of a well-developed symplicate zone in its gynoecium, as well as in the ovule insertion in the symplicate zone (rather than in the cross-zone). The present investigation re-examined the floral structure of Seemannaralia with emphasis on the morphology and evolution of its gynoecium.

Methods

Flowers and fruits of Seemannaralia gerrardii at various developmental stages were examined using light microscopy and scanning electron microscopy.

Key Results

Ovaries in the flowers of Seemannaralia are bilocular. Each ovary locule corresponds to a carpel whose ascidiate part is distinctly longer than the plicate part. Each carpel contains one fertile ovule attached to the cross-zone, and one sterile ovule as well. The fruit is unilocular: its central cavity is occupied by a single large seed. In the course of fruit development, the growth of one ovule stops while another ovule develops into the mature seed. When this ovule outgrows the available space in the locule, the septum is ruptured, forming a united cavity of two carpels.

Conclusions

Despite literature data, the synascidiate zone is well developed in the gynoecium of Seemannaralia, and the ovules are attached to the cross-zone. Its preanthetic and anthetic gynoecium has nearly the same structure as gynoecia of most other Araliaceae. The Seemannaralia fruit resembles the paracarpous gynoecium but its ground plan is very different because the central cavity is formed by mechanical rupture of the septum. The term ‘pseudoparacarpy’ (‘false paracarpy’) is proposed to describe this condition, which has not been reported to date for indehiscent fruits in any taxa other than Seemannaralia. In this genus, the pseudoparacarpy has probably resulted from a decrease in seed number in the course of the transition from zoochory to anemochory.     

Flower and fruit characters in the early-divergent lamiid family Metteniusaceae, with particular reference to the evolution of pseudomonomery

Evaluating the morphological relationships of angiosperm families that still remain unplaced in the current systems of classification is challenging because it requires comparative data across a broad phylogenetic range. The small neotropical family Metteniusaceae was recently placed within the lamiids, as sister to either the enigmatic Oncothecaceae or the clade (Boraginaceae + Gentianales + Lamiales + Solanales + Vahliaceae). We examined the development of two of the primary diagnostic traits of Metteniusaceae, the moniliform anthers and the unilocular gynoecium. The gynoecium is 5-carpellate, and contains two ovules with a massive, vascularized integument. Late sympetaly and unitegmic ovules support placement of Metteniusaceae in the lamiids. The 5-carpellate gynoecium is consistent with a sister-group relationship between Metteniusaceae and Oncothecaceae. The gynoecium of Metteniusaceae is unusual in that it is monosymmetric throughout ontogeny, which indicates pseudomonomery; the five carpel initials are congenitally fused by their margins and form a single locule; the two ovules develop from the two smallest and most poorly developed lateral carpels. Comparisons with other pseudomonomerous taxa allow us to propose division of the complex processes leading to pseudomonomery into eight characters, including carpel number and fusion, gynoecial symmetry, timing of carpel reduction, and number and position of nonfertile carpels.     

Within-carpel and among-carpel competition during seed development, and selection on carpel number, in the apocarpous perennial herb Helleborus foetidus L. (Ranunculaceae)

Apocarpous flowers share opportunities for post-fertilization ovule selection among more functional levels than syncarpous flowers, because the occurrence of a variable number of unfused carpels adds a new source of variation to the likelihood of successful female reproduction. The extent to which post-fertilization events might differ among these unfused carpels may promote variations in the reproductive strategies of plants. We report a study of the variation, within and among carpels and flowers, in seed production and mass in the apocarpous Helleborus foetidus (Ranunculaceae), in relation to the number of carpels per flower. Differences within and among carpels in female reproductive success were affected by carpel number and pollination environment. When analysing whole flowers as functional units we also found that the magnitude of the differences related to carpel number and pollination treatment actually depended on the “distribution” of pollen types within flowers. Thus, variable within-flower pollination environments, more likely to occur in apocarpous than in syncarpous flowers, may affect the strategies of resource allocation for fruit development at different stages of the reproductive process. Regarding seed production, we found that producing more flowers with four carpels was under directional; however, when mean diaspore mass was considered as a measure of fitness, directional selection was found on producing flowers with two and three carpels (the modal carpel number found in wild populations). We discuss ecological and developmental reasons which could explain the observed pattern, and conclude that selection on an optimum carpel number may be very variable across the species range, as the discussed reasons may impose constraints on eventual evolutionary response, thus contributing to the maintenance of the intra-individual variability in carpel number.     

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.