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.     

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.     

Ontogeny and evolution of the flowers of South African Restionaceae with special emphasis on the gynoecium

 The South African Restionaceae make up a highly diverse group of genera displaying several reductive trends in the configuration of the flower, especially in the gynoecium. In this paper the floral ontogeny of fourteen species representing nine of the 11 genera of the Restio clade is studied with the SEM. Although flowers are basically simple, the variability in both mature and developmental stages is striking. Differences between species are the result of changes in growth rate, coupled with differential pressures of organs. Trends in the elaboration of bracts, perianth, androecium and gynoecium are compared. Together with data that have been presented elsewhere about the other clade of African Restionaceae, viz. the Willdenowia-clade, a scheme with potential developmental pathways is proposed and the most evident routes are selected based on ontogenetic evidence. Nine possible reductions are presented arising through three main routes. Received August 27, 2001 Accepted October 26, 2001     

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.     

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     

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.     

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.     

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.     

Female flowers and inflorescences of Didymelaceae

 In molecular analyses Didymelaceae together with Buxaceae form a fairly well-supported clade among families near the base of eudicots. Only little is known, however, about the flowers and inflorescences of Didymelaceae. In this study, the structure of the female flowers and inflorescences of Didymeles integrifolia was studied. Flowers are unicarpellate and orientation of the carpel is slightly deflected abaxially as in Proteaceae. Otherwise, Didymelaceae share many features of the gynoecium with Buxaceae and some other basal eudicots: the carpels are ascidiate in the lower half; anthetic carpels are completely closed by postgenital fusion; stigma is double-crested and widely decurrent; stigmatic papillae are unicellular and pear-shaped; the pollen tube transmitting tract is extensive and prominently differentiated; fruits are fleshy drupes with persistent stigma and style. However, the exceedingly elongate base of the integuments of Didymelaceae is an unusual feature among basal eudicots and even angiosperms. Received October 31, 2002; accepted December 17, 2002 Published online: March 31, 2003     

Developmental morphology of female flowers of Gyrostemon and Tersonia and floral evolution among Gyrostemonaceae

Floral simplifications and specializations in the evolution of Gyrostemonaceae have confused the systematics of the family. Recent phylogenetic analyses have demonstrated their placement among Capparales. This investigation presents a phylogenetic analysis of Gyrostemonaceae, demonstrating that Codonocarpus and Gyrostemon form a clade that is the sister group of Cypselocarpus, Tersonia, and Walteranthus. These phylogenetic results and data on development of Gyrostemon and Tersonia are used to discuss the morphology and evolutionary diversification of female flowers of Gyrostemonaceae. The uniseriate perianth of Gyrostemonaceae consists of four to eight tepals with an unusual lateral to median developmental sequence. The female flowers of Gyrostemon and Tersonia display no distinctive evidence of an androecium, although the former has late-forming, primordium-like structures positioned between the tepals and gynoecium that may be the vestiges of either a second perianth series or the androecium. The gynoecium of Gyrostemonaceae is syncarpous, although the two main clades in the family differ in the expression of ovarian synorganization. The Codonocarpus–Gyrostemon clade is unusual in having largely separate carpels that are only syncarpous because the ventral side of each is formed by the flank of the floral apex. All Gyrostemonaceae, however, incorporate the flank of the floral apex as the ventral side of the carpel, and this is the location of ovule development. On the basis of its placement in a clade that includes Tersonia and Walteranthus, the uniloculate and uniovulate gynoecium of Cypselocarpus may be pseudomonomerous. All Gyrostemonaceae have large stigmas that are typical of anemophilous taxa, and they differ from most other Capparales in this attribute. Among Capparales, Gyrostemonaceae may be most similar to Ochradenus (Resedaceae), which also appears to be anemophilous. It is unclear whether the similarities of Ochradenus and Gyrostemonaceae are homologies, indicative of a close relationship between the two groups, or evolutionary parallelisms associated with separate shifts to anemophily.     

Molecular Phylogeny of Casuarinaceae Based on rbcL and matK Gene Sequences

rbcL (1310 bp) and matK (1014 bp), using 15 species representing the family. The study included analyses of Ticodendron (Ticodendraceae) and three species of Betulaceae as close relatives, and one species each of Juglandaceae and Myricaceae as outgroups. Analyses based on matK gene sequences, which provided a much better resolution than the analyses based on rbcL gene sequences alone, resulted in a single most parsimonious tree whose topology is almost identical with the strict consensus tree generated by the combined data set of rbcL and matK gene sequences. Results showed that Casuarinaceae are monophyletic, comprising four distinct genera, Allocasuarina, Casuarina, Ceuthostoma and Gymnostoma, which were not recognized until recently. Within the family, Gymnostoma is positioned at the most basal position and sister to the remainder. Within the remainder Ceuthostoma is sister to the Allocasuarina-Casuarina clade. Morphologically the basalmost position of Gymnostoma is supported by plesiomorphies such as exposed stomata in the shallow longitudinal furrows of the branchlets, a basic chromosome number x=8 and the gynoecium composed of two fertile, biovulate carpels. The three other genera, Allocasuarina, Casuarina, and Ceuthostoma, have invisible stomata in the deep longitudinal furrows of the branchlets, a higher basic chromosome number x=9 or 10–14 (unknown in Ceuthostoma), the gynoecium composed of one fertile and one sterile carpel with a single ovule (unknown in Ceuthostoma). The diversity of infructescence morphology found in the latter three genera suggests that they may have evolved in close association with the elaboration of fruit dispersal mechanisms. Received 14 September 2001/ Accepted in revised form 12 October 2001     

INFLORESCENCE AND FLOWER DEVELOPMENT IN THE PIPERACEAE III. FLORAL ONTOGENY OF PIPER

Floral development in Piper was compared between four-staminate species (P. aduncum and P. marginatum) and six-staminate species (P. amalago). All Piper species have a syncarpous gynoecium composed of three or four carpels. The floral apex is initiated by a periclinal division in the subsurface layer in the axil of a bract 40-55 μm high; initiation of the bracts occurs separately and considerably earlier. The floral primordium widens and the first pair of stamens are initiated at either side. The median anterior stamen forms next, and the median posterior later. This sequence is common to all species studied. In the six-staminate P. amalago, the last two stamens form simultaneously in lateral-anterior positions. The stamens hence arise as pairs, and symmetry is bilateral or dorsiventral. The three or four carpels arise simultaneously; they are soon elevated on a gynoecial ring by growth of the receptacle below the level of attachment of the carpels to produce a syncarpous gynoecium. The floral apex lastly produces the solitary basal ovule and is used up in its formation.     

STUDIES ON THE FLORAL ANATOMY OF THE CUNONIACEAE

Twenty-two genera representing sixty-two species of Cunoniaceae and Davidsonia were examined with respect to floral anatomy. Sepals are vascularized by three traces with the lateral traces of adjacent sepals united. Pancheria is unique for the family with species in which the sepals are vascularized by a single, undivided bundle. Petals, when present, and stamens, are uniformly one-trace structures. A general tendency exists within the family for the principal floral bundles to unite in various ways, with fusions evident between calyx, corolla, and androecial vascular supplies. Carpel number ranges from two to five and the gynoecium is generally surrounded by a prominent disc. Gynoecia of Ceratopetalum and Pullea are “half-inferior.” The number of ovules per carpel locule ranges from one to numerous. Ventral carpel sutures range from open to completely sealed at the level of placentation. Carpels of the apocarpous genus Spiraeanthemum (incl. Acsmithia) are vascularized by a dorsal bundle and either three or four bundles constituting the ovular and wing vasculation in the ventral position, a condition unlike other members of the family. Ovules are supplied by the median ventral bundle. More advanced bicarpellate gynoecia within the family are predominately vascularized by a dorsal and two ventral bundles although a variable number of additional lateral wall traces may be present. A major trend exists toward fusion of the ventral bundles of adjacent carpels in the ovary of both bicarpellate and multicarpellate plants. At the base of the styles the fused ventral strands separate and extend along with the dorsal carpellary bundles into styles of adjacent carpels. In Pullea the ventral bundles terminate within the ovules. The united ventral carpellary bundles in Aphanopetalum, Gillbeea, and Aistopetalum lie in the plane of the septa separating adjacent carpels. Ovules are vascularized by traces originating from the vascular cylinder at the base of the gynoecium or by traces branching from the ventral bundles. Ovular traces in each carpel are united, or remain as discrete bundles, prior to entering the placenta. Tannin and druses are common throughout all floral parts. Although floral anatomy generally supports the position of Cunoniaceae near Saxifragaceae and Davidsoniaceae, the evolutionary relationship of the Cunoniaceae to the Dilleniaceae is uncertain.     

POSTGENITAL CARPEL FUSION IN CATHARANTHUS ROSEUS (APOCYNACEAE). I. LIGHT AND SCANNING ELECTRON MICROSCOPIC STUDY OF GYNOECIAL ONTOGENY

The detailed ontogeny of postgenital fusions within the gynoecium of Catharanthus roseus was investigated. The basal margins of the young carpel primordia infold and fuse together to seal shut the loculi. Independently, the opposing distal tips of the two carpels also unite, with the fusion region subsequently developing into the stigma, style, and a small distal region of the compound ovary. The basal ovary regions of the two opposing carpels remain unfused, thus leaving the tip fusion spatially restricted. In the region of contact, cells with distinctively epidermal features progressively lose their epidermal character after their participation in the fusion. In the fused stigma these former epidermal cells redifferentiate into transmitting and secretory tissues; in the fused style these cells undergo a tremendous expansion in length while forming stylar transmitting tissue; but in the compound ovary region corresponding cells experience little expansion or redifferentiation. It is concluded that the loss of epidermal features or the occurrence of periclinal cell divisions in the epidermis is a definitive indication that cells have fused postgenitally. However, studies with the transmission electron microscope are necessary to detect the first indications of a postgenital fusion. The compound ovary region within the gynoecium of C. roseus is a tissue appropriate for a high resolution ultrastructural study of the cytological events accompanying postgential tissue fusion because the fusion occurs quickly and little subsequent cell expansion takes place within this region.     

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.     

Floral organogenesis in Tetracentron sinense (Trochodendraceae) and its systematic significance

In Tetracentron sinense of the basal eudicot family Trochodendraceae, the flower primordium, together with the much retarded floral subtending bract primordium appear to form a common primordium. The four tepals and the four stamens are initiated in four distinct alternating pairs, the first tepal pair is in transverse position. The four carpels arise in a whorl and alternate with the stamens. This developmental pattern supports the interpretation of the flower as dimerous in the perianth and androecium, but tetramerous in the gynoecium. There is a relatively long temporal gap between the initiation of the stamens and the carpels. The carpel primordia are then squeezed into the narrow gaps between the four stamens. In contrast to Trochodendron, the residual floral apex after carpel formation is inconspicuous. In their distinct developmental dimery including four tepals and four stamens, flowers of Tetracentron are reminiscent of other, related basal eudicots, such as Buxaceae and Proteaceae.     

Pistillate and staminate flower development in dioecious Pistacia vera (Anacardiaceae)

The development of staminate and pistillate flowers in the dioecious tree species Pistacia vera L. (Anacardiaceae) was studied by scanning electron microscopy with the objective of determining organogenetic patterns and phenology of floral differentiation. Flower primordia are initiated similarly in trees of both sexes. Stamen and carpel primordia are initiated in both male and female flowers, and the phenology of organ initiation is essentially identical for flowers of both sexes. Vestigial stamen primordia arise at the flanks of pistillate flower apices at the same time functional stamens are initiated in the staminate flowers. Similarly, a vestigial carpel is initiated in staminate flowers at the same time the primary, functional carpel is initiated in pistillate flower primordia. Differences between the two sexes become apparent early in development as, in both cases, development of organs of the opposite sex becomes arrested at the primordial stage. Male flowers produce between four and six mature functional stamens and female flowers produce a gynoecium with one functional and two sterile carpels.     

INFLORESCENCE AND FLORAL DEVELOPMENT IN HOUTTUYNIA CORDATA (SAURURACEAE)

The inflorescence of Houttuynia cordata produces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle-core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant, Saururus cernuus. Exceptions to this unusual development, however, occur in H. cordata at the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity in H. cordata when primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last-formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition in Houttuynia is the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.     

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.     

ANATOMY OF THE GYNOECIUM IN TWO SPECIES OF BAKERIDESIA (MALVACEAE)

Structure of the gynoecium is described in two species of Bakeridesia, subgenus Bakeridesia (Malvaceae, tribe Malveae). The dorsal wall of each carpel bears a winglike projection with a marginal pair of pubescent, bluntly dentate wings. The projection arises as a single, solid ridge of tissue after the ovules are initiated and after the ventral carpellary margins are fused with the receptacle. Two multiseriate layers of fiber-sclereids line each locule and continue into the winglike projection where they are separated by parenchyma. Gynoecial vascularization is described in detail. The richly vascularized carpels are supplied by five traces: a median dorsal trace, which bifurcates into two dorsal bundles; two lateral traces; and two ventral traces. Adjacent ventral traces, lateral traces, and septal bundles are fused—i.e., they are held in common by neighboring carpels. The presence of lateral carpellary traces may be a primitive character in the tribe Malveae.