Floral Ontogeny Research Articles

Elaborate Petals in Australian Spermacoce (Rubiaceae) Species: Morphology, Ontogeny and Function

Australian Spermacoce species display various types of elaborate petals. Their precise morphology, ontogenetic origin, and function are hitherto unknown. The aim of the present paper is to unravel the development and nature of the diverse types of elaborate petals in Spermacoce through a floral ontogenetic study. The floral ontogeny of six species characterized by different types of corolla appendages was studied by scanning electron microscopy and light microscopy. In order to elucidate the possible functions of the elaborate petals, field observations were conducted as well. Scanning electronmicrographs show that full-grown petals of Spermacoce lignosa, S. phaeosperma and S. redacta bear appendages on their ventral side. Despite their different appearance at anthesis, the appendages develop very similarly in all three species. They are initiated at the same developmental stage and are first visible as two arcs of primordia converging from the upper margins of the petal towards its midvein and downwards. In S. brevidens, S. caudata and S. erectiloba, the full-grown petals have two long, concave protuberances, which develop from the tissue at both sides of the petal's mid-vein. In these three species, initiation of appendages on the ventral side of the petals is also observed, but they are hardly visible on the mature petals. The two types of elaborate petals tightly enclose the anthers, both in bud and during most of the flowering period. Among Australian Spermacoce species, two types of elaborate petals can be distinguished. The former hypothesis that the two types of elaborate petals are essentially homologous is here rejected. Field investigations point out that the elaborate petals might play a role in the pollination biology of the species.

Floral ontogeny, petal diversity and nectary uniformity in Bruniaceae

Bruniaceae are a small family subendemic to the Cape Floristic Region. Flowers are actinomorphic, choripetalous, pentamerous and tetracyclic. The petals show diverse adaxial swellings, which have been quoted as an example of diplophylly. Developmental studies confirm the true choripetaly of the flowers, thus pointing to an affinity to the Apiales within the euasterids II. They reject, however, the hypothesis of diplophylly as the petal swellings grow out rather late and are not vascularized. According to the position, size and shape of the swellings, six petal types are distinguished, which in part have phylogenetic information. Nectaries occur on the upper part of the ovary. Nectar is exuded through modified stomata serving as secretory channels. All genera have gynoecial nectaries of the mesenchymatous type. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150, 459–477.

Floral structure and ontogeny in Globba (Zingiberaceae)

We present new comparative morphological and ontogenetic data on flowers and bulbils of Globba (Zingiberaceae) to clarify their homologies. Globba flowers are characteristically Zingiberaceous, possessing a single stamen and epigynous (``supragynopleural'') nectaries, but are unusual as the anther bears triangular lateral outgrowths and the style is held tightly in position across the curvature of the filament like a bowstring. Floral ontogeny in Globba is similar to other Zingiberaceae. Characteristic features, such as anther wings, occur late in development, shortly before anthesis. Unusually Globba has zygomorphic style anatomy with only two abaxial vascular bundles, in contrast to most other Zingiberaceae, which possess three stylar traces. The ovary is unilocular and lacks septa. Bulbils have enclosing bracts and replace flowers in the lower part of the inflorescence; they consist of a shoot with an enlarged corky storage root forming the bulk of the propagule.

Floral organ identity genes in the orchid Dendrobium crumenatum

Orchids are members of Orchidaceae, one of the largest families in the flowering plants. Among the angiosperms, orchids are unique in their floral patterning, particularly in floral structures and organ identity. The ABCDE model was proposed as a general model to explain flower development in diverse plant groups, however the extent to which this model is applicable to orchids is still unknown. To investigate the regulatory mechanisms underlying orchid flower development, we isolated candidates for A, B, C, D and E function genes from Dendrobium crumenatum. These include AP2-, PI/GLO-, AP3/DEF-, AG- and SEP-like genes. The expression profiles of these genes exhibited different patterns from their Arabidopsis orthologs in floral patterning. Functional studies showed that DcOPI and DcOAG1 could replace the functions of PI and AG in Arabidopsis, respectively. By using chimeric repressor silencing technology, DcOAP3A was found to be another putative B function gene. Yeast two-hybrid analysis demonstrated that DcOAP3A/B and DcOPI could form heterodimers. These heterodimers could further interact with DcOSEP to form higher protein complexes, similar to their orthologs in eudicots. Our findings suggested that there is partial conservation in the B and C function genes between Arabidopsis and orchid. However, gene duplication might have led to the divergence in gene expression and regulation, possibly followed by functional divergence, resulting in the unique floral ontogeny in orchids.

Floral ontogeny of Cneorum tricoccon L. (Rutaceae)

The floral ontogeny of the Spurge olive (Cneorum tricoccon L.) is studied by means of scanning electron microscopic observations. Special attention is paid to the sequence of initiation of the floral parts, the occurrence of septal cavities, and the development of the nectariferous tissue. The nectary disc arises as a receptacular outgrowth below the ovary and independently from stamen development. By the extensive growth of this voluminous androgynophore, stamen filaments become enclosed by nectary tissue and as a result, they are seated in pits between the lobes of the disc. Between ovary and style, three lobes are present, which are covered with stomata – their function is unknown. The significance of the unusual trimery of the flower is discussed. Floral developmental evidence supports a Rutalean affinity, although more ontogenetic investigations are needed in Rutaceae, subfamily Spathelioideae.

Floral ontogeny of Hardenbergia violacea (Fabaceae: Faboideae: Phaseoleae) and taxa of tribes Bossiaeeae and Mirbelieae, with emphasis on presence of pseudoraceme inflorescences

The floral ontogeny of several Australian papilionoid taxa has been studied in Hardenbergia violacea L. (Phaseoleae); Kennedia rubicunda (Phaseoleae; inflorescences only); Bossiaea cordigera (Bossiaeeae); Gastrolobium truncatum, Mirbelia oxylobioides, and Pultenaea daphnoides (Mirbelieae). Species studied of Hardenbergia, Pultenaea, and Brachysema have pseudoracemose inflorescences comprised of triads of flowers, Kennedia rubicunda has paired flowers that resemble reduced pseudoracemes, while Gastrolobium truncatum and Mirbelia oxylobioides have pseudoracemes comprised of 2–10 flowers per ultimate unit. Pseudoracemes are a significant and overlooked feature in many taxa of tribes Bossiaeeae and Mirbelieae. Hardenbergia violacea has ultimate axillary units of three flowers, each with a subtending bract but no bracteoles. Floral ontogeny in H. violacea and P. daphnoides shows acropetal order among whorls, and unidirectional order starting from the abaxial side in sepal, petal, and stamen whorls, as in most papilionoid flowers. The carpel is initiated concurrently with the first antesepalous stamen primordium. Pultenaea daphnoides and Bossiaea cordigera have unidirectional sepal initiation starting abaxially, but simultaneous petal initiation, an unusual feature among papilionoids. In late stages of H. violacea and B. cordigera, a diadelphous stamen tube or sheath is formed, while in taxa of Mirbelieae the stamens remain free. The flowers in all taxa studied become strongly zygomorphic as evidenced by three petal morphs and upturning of the free portions of style and stamens late in development.

Evolutionary Transitions among Flowers of Perianthless Piperales: Inferences from Inflorescence and Flower Development in the Anomalous SpeciesPeperomia fraseri(Piperaceae)

Floral and inflorescence structure and ontogeny are described in detail in Peperomia fraseri, an anomalous species of Piperaceae that differs in several respects from other species of Peperomia and other perianthless Piperales (Piperaceae and Saururaceae). Inflorescence structure is atypical in this species, with numerous spikes arranged spirally on a long raceme. There is a gender distribution of flowers along each spike, with the proximal (lower) part bearing bisexual flowers and the distal (upper) region bearing female flowers. Furthermore, there is a high degree of polymorphism in the structure (including presence or absence) of flower‐subtending bracts in the same inflorescence. Bract suppression at the basalmost abaxial position in P. fraseri could be explained by a strong inhibitory activity of the spike‐subtending bract or its primordium. Bract suppression among scattered flowers in the lower (bisexual) region is interpreted as an example of somatic instability. By contrast, more distal bract and ...

Floral Ontogeny in Ficinia and Isolepis (Cyperaceae), with Focus on the Nature and Origin of the Gynophore

The generic delimitations of Ficinia and Isolepis, sister genera in the Cypereae, are blurred. Typical Ficinia flowers have a lobed gynophore, which envelops the base of the nutlet, whereas in Isolepis the character is considered to be absent. Some former species of Isolepis, lacking the gynophore, were recently included in Ficinia. The floral ontogeny of representative taxa in Ficinia and Isolepis were investigated with the aim of evaluating the origin and nature of the gynophore in the Cypereae. The spikelet and floral ontogeny in inflorescences collected in the field was investigated using scanning electron microscopy (SEM) and light microscopy (LM). SEM images of Isolepis setacea and I. antarctica, Ficinia brevifolia, F. minutiflora, F. zeyheri and F. gracilis, and LM sections of F. radiata, show that the gynoecium in Ficinia is elevated above the flower receptacle by the development of a hypogynous stalk. From its apex, a (often three-)lobed cup is formed, which envelopes the basal part of the later nutlet. In developing flowers of I. antarctica, a rudimentary hypogynous stalk appears. In I. setacea, rudiments of a hypogynous stalk can be observed at maturity. In F. radiata and F. zeyheri, intralocular hairs are present in the micropylar zone. At the surface of developing gynoecia in flowers of F. gracilis, star-shaped cuticular structures appear which disappear again at maturity. The overall floral ontogeny of all species studied occurs following a typical scirpoid pattern, though no perianth primordia are formed. The gynophore in Ficinia originates as a hypogynous stalk, from which the typical gynophore lobes develop. The gynophore is not homologous with the perianth.

Functional conservation of PISTILLATA activity in a pea homolog lacking the PI motif.

Current understanding of floral development is mainly based on what we know from Arabidopsis (Arabidopsis thaliana) and Antirrhinum majus. However, we can learn more by comparing developmental mechanisms that may explain morphological differences between species. A good example comes from the analysis of genes controlling flower development in pea (Pisum sativum), a plant with more complex leaves and inflorescences than Arabidopsis and Antirrhinum, and a different floral ontogeny. The analysis of UNIFOLIATA (UNI) and STAMINA PISTILLOIDA (STP), the pea orthologs of LEAFY and UNUSUAL FLORAL ORGANS, has revealed a common link in the regulation of flower and leaf development not apparent in Arabidopsis. While the Arabidopsis genes mainly behave as key regulators of flower development, where they control the expression of B-function genes, UNI and STP also contribute to the development of the pea compound leaf. Here, we describe the characterization of P. sativum PISTILLATA (PsPI), a pea MADS-box gene homologous to B-function genes like PI and GLOBOSA (GLO), from Arabidopsis and Antirrhinum, respectively. PsPI encodes for an atypical PI-type polypeptide that lacks the highly conserved C-terminal PI motif. Nevertheless, constitutive expression of PsPI in tobacco (Nicotiana tabacum) and Arabidopsis shows that it can specifically replace the function of PI, being able to complement the strong pi-1 mutant. Accordingly, PsPI expression in pea flowers, which is dependent on STP, is identical to PI and GLO. Interestingly, PsPI is also transiently expressed in young leaves, suggesting a role of PsPI in pea leaf development, a possibility that fits with the established role of UNI and STP in the control of this process.

Floral Ontogeny in Scirpus, Eriophorum and Dulichium (Cyperaceae), with Special Reference to the Perianth

Floral Ontogeny in Scirpus, Eriophorum and Dulichium (Cyperaceae), with Special Reference to the Perianth

Floral Ontogeny of Aquilegia, Semiaquilegia, and Enemion (Ranunculaceae)

Using scanning electron microscopy, we studied the comparative floral ontogeny of closely related taxa in the tribe Isopyreae of the Ranunculaceae (Aquilegia olympica, Aquilegia ecalcarata, Semiaquilegia adoxoides, and Enemion occidentale) that vary in a number of floral features. Phylogenetic reconstruction of the Isopyreae indicates that floral nectar spurs are derived in Aquilegia (but secondarily lost in A. ecalcarata), lack of petals is derived in Enemion, and staminodia are derived in $$Aquilegia+Semiaquilegia$$. Order of initiation is shared among all species studied: helical for sepals and simultaneous whorled for all other organs. Species of Aquilegia all have 10 orthostichies (vertical rows of organs), with alternate orthostichies either sepal based or petal based. Scalelike staminodes terminate the orthostichies of stamens in Aquilegia; these staminodes are few or absent in Semiaquilegia and other Ranunculaceae. Carpels terminate the sepal‐based orthostichies. Organogenesis in Enemion and A. ecalcarata are similar except that the alternisepalous orthostichies contain only stamens in Enemion and lack petals. Spurs in A. olympica originate as an abaxial bulge late in petal development that projects downward. Despite the inference that the lack of spurs is ancestral in S. adoxoides but derived in A. ecalcarata, their early petal development is remarkably similar, with the formation of an abaxial knob that fails to develop further. This indicates that A. ecalcarata has lost a key early developmental feature for spur development. Lack of petals in Enemion has clearly resulted from a homeotic shift as stamens develop in the same position as petals in the other species. In Aquilegia and Semiaquilegia, flowers with more stamens have more staminodia. This pattern indicates that staminodia may represent the addition of a novel floral whorl rather than simply a suppression of the development of some stamens. Variation in floral features in other members of the Isopyreae suggests that this tribe will be especially fruitful for future morphological and molecular studies of flower development.

Floral Ontogeny in Scirpus, Eriophorum and Dulichium (Cyperaceae), with Special Reference to the Perianth

Based on molecular phylogenetic analysis, it has been suggested recently that the Cyperaceae comprises only two subfamilies: the Mapanioideae and the Cyperoideae. In most flowers of the Cyperoideae, the whorl of inner stamens is reduced, resulting in tetracyclic flowers. In the more primitive (scirpoid) genera within the Cyperoideae, the perianth consists of two polysymmetric whorls, whereas the perianth parts in the more derived genera have been subject to modifications and/or reduction. Comparative studies of the many silky hairs of Eriophorum and of the eight bristles of Dulichium have given rise to much discussion about their homology. The spikelet and floral ontogeny in freshly collected inflorescences was investigated using scanning electron microscopy. Complete floral ontogenies are presented for Scirpus sylvaticus L., Eriophorum latifolium Hoppe and Dulichium arundinaceum (L.) Britton, with special reference to the perianth. The results in S. sylvaticus confirm the trimerous monocot-like organization of the flower. It is used as a model for floral development in Cyperoideae. In the early developmental stages, the androecium of E. latifolium is surrounded by a massive perigonial primordium, from which the many hair-like bristles originate. Consequently, the stamens develop among the hair primordia, more or less simultaneously. The hairs are arranged in whorls, which develop centripetally. The development of the perianth in D. arundinaceum starts with the formation of three initial perianth primordia opposite the stamens. Subsequently, two more abaxial bristle primordia, alternating with the stamens, originate simultaneously with the appearance of three adaxial bristle primordia in the zone where an adaxial inner perianth primordium is expected. The floral development in E. latifolium and D. arundinaceum can be considered as variations upon the scirpoid floral ontogenetic theme.

Floral Ontogeny and Allometry ofMimulus cardinalis: Interpopulational Variation and Traits of the Hummingbird‐Pollination Syndrome

Investigations of floral ontogeny and allometry were used to determine the developmental origins of morphological variation among population samples of Mimulus cardinalis and the origins of floral characters that favor pollination by hummingbirds. Dimensions of structures in all whorls of the flowers differ among populations. Although the size and shapes of floral apices differ, the initiation sequence and enlargement of primordia and organogenesis are similar among populations. Interpopulational differences in calyx and corolla length result from distinct rates of growth and times of termination of growth. Stamen and style lengths vary among populations primarily because of different times of termination of growth. Inequalities in duration of growth explain variation in lengths of corolla tubes below the region of stamen insertion. Traits suited to hummingbird pollination, such as a longer upper wall of the corolla and the resulting oblique corolla aperture, are determined by different rates of growth between the upper and lower corolla walls. Upper and lower stamen pairs also grow at different rates. Other traits, such as a nectar gate between the basal ovarian nectary and bases of the lower filaments and stamens positioned in the upper medial region of the corolla, are caused by differential growth of regions of the filaments. Aspects of the ontogeny of M. cardinalis that influence morphological traits characteristic of the hummingbird‐pollination syndrome are related to published data on hummingbird pollination.

Floral development and systematic position of Arillastrum, Allosyncarpia, Stockwellia and Eucalyptopsis (Myrtaceae)

We have investigated the floral ontogeny of Arillastrum, Allosyncarpia, Stockwellia and Eucalyptopsis (of the eucalypt group, Myrtaceae) using scanning electron microscopy and light microscopy. Several critical characters for establishing relationships between these genera and to the eucalypts have been determined. The absence of compound petaline primordia in Arillastrum, Allosyncarpia, Stockwellia and Eucalyptopsis excludes these taxa from the eucalypt clade. Post-anthesis circumscissile abscission of the hypanthium above the ovary in Stockwellia, Eucalyptopsis and Allosyncarpia is evidence that these three taxa form a monophyletic group; undifferentiated perianth parts and elongated fusiform buds are characters that unite Stockwellia and Eucalyptopsis as sister taxa. No floral characters clearly associate Arillastrum with either the eucalypt clade or the clade of Stockwellia, Eucalyptopsis and Allosyncarpia.

The nature of the perianth in Fuirena (Cyperaceae)

The genus Fuirena Rottb. is currently classified in the tribe Fuireneae Reichenbach ex Fenzl (subfamily Cyperoideae), based on the presence of spikelets with many spirally arranged glumes, each subtending a bisexual flower, and because of unique embryo characters. The trimerous Fuirena flowers have two whorls of perianth parts that show a wide morphological variety and various reduction trends. In flowers of F. ciliaris (L.) Roxb., the outer whorl consists of three bristle-like perianth parts opposite the stamens. The three scale-like inner perianth parts alternate with the stamens. The nature and exact position of the inner perianth parts have long been a subject for discussion. In the context of the 'synanthium' hypothesis, some authors have interpreted the perianth parts as floral bracts. Alternatively, the inner perianth parts have also been interpreted as staminodia because of their appearance and position. In this study we present new evidence in favour of a conventional monocotyledonous pentacyclic flower model in Cyperoideae based on SEM observations on the floral ontogeny of F. ciliaris, F. leptostachya Oliver, F. abnormalis C.B.Clarke and F. pubescens (Poir.) Kunth. Our observations confirm a pentacyclic organisation of the flowers within Fuirena, and they corroborate the interpretation of the inner scales and outer bristles as perianth parts.

Floral development of Berberidopsis corallina: a crucial link in the evolution of flowers in the core Eudicots.

On the basis of molecular evidence Berberidopsidaceae have been linked with Aextoxicaceae in an order Berberidopsidales at the base of the core Eudicots. The floral development of Berberidopsis is central to the understanding of the evolution of floral configurations at the transition of the basal Eudicots to the core Eudicots. It lies at the transition of trimerous or dimerous, simplified apetalous forms into pentamerous, petaliferous flowers. The floral ontogeny of Berberidopsis was studied with a scanning electron microscope. Flowers are grouped in terminal racemes with variable development. The relationship between the number of tepals, stamens and carpels is more or less fixed and floral initiation follows a strict 2/5 phyllotaxis. Two bracteoles, 12 tepals, eight stamens and three carpels are initiated in a regular sequence. The number of stamens can be increased by a doubling of stamen positions. The floral ontogeny of Berberidopsis provides support for the shift in floral bauplan from the basal Eudicots to the core Eudicots as a transition of a spiral flower with a 2/5 phyllotaxis to pentamerous flowers with two perianth whorls, two stamen whorls and a single carpel whorl. The differentiation of sepals and petals from bracteotepals is discussed and a comparison is made with other Eudicots with a similar configuration and development. Depending on the resolution of the relationships among the basalmost core Eudicots it is suggested that Berberidopsis either represents a critical stage in the evolution of pentamerous flowers of major clades of Eudicots, or has a floral prototype that may be at the base of evolution of flowers of other core Eudicots. The distribution of a floral Bauplan in other clades of Eudicots similar to Berberidopsidales is discussed.

Floral ontogeny in Lespedeza thunbergii (Leguminosae: Papilionoideae: Desmodieae): variations from the unidirectional mode of organ formation.

Floral ontogeny of Lespedeza thunbergii was studied with the use of scanning electron microscopy (SEM). The ontogeny varies in all whorls from the undirectional mode, which has been long held to be the rule in Leguminosae. In the sepal whorl, the lateral and the adaxial sepals are formed simultaneously, which is interpreted as a tendency towards whorled organ formation. Whorled organ formation is shown in the petal whorl. The antesepalous stamen whorl varies least from the unidirectional mode. Here, the adaxial stamens are formed successively. This is seen as a remnant of an original helical organ formation in Papilionoideae. Within the antepetalous stamen whorl, the two abaxial stamens and the adaxial stamen are formed first, followed by the two lateral stamens. This is a rarely found phenomenon, which is hard to interpret at the present state of knowledge. Concerning the mature flower, it is shown that nectar stomata are found in a distinct area on the adaxial side of the flower. The presented "new" characteristics should be an initial step toward further work on taxa of the tribe Desmodieae. These studies will broaden the data set and enable a detailed phylogenetic analysis.

Floral Organogenesis in Plowmanianthus (Commelinaceae)

Floral organogenesis in three species of Plowmanianthus (subtribe Dichorisandrinae; tribe Tradescantieae) is described. Development begins as in other commelinaceous monosymmetric or monosymmetric‐derived flowers for which comparable data are available, with the precocious development of the upper (outer) sepal. Later, six stamen primordia emerge from the floral apex, but the lower three are soon aborted such that there are only three stamens at anthesis. Development of the lower petal is precocious. That is, although all three petals are at first similar in size and appearance following their simultaneous or nearly simultaneous initiation, the lower petal expands much more rapidly than either of the inner petals and initiates its fringe of moniliform hairs first. Early and middle phases of floral ontogeny in Plowmanianthus most closely resemble those of the closely related Cochliostema, especially in regards to suppression of the lower stamens and the laterally appressed, introrsely oriented, strongly curved anther thecae of the upper stamens. The staminal features unique to Cochliostema, such as union and curvature of the filaments, spiraling of the thecae, and development of filament‐borne structures enveloping the anthers, occur relatively late in development in this genus and are lacking in Plowmanianthus. Floral ontogenetic studies are still needed for other Dichorisandrinae, such as Geogenanthus, Siderasis, and additional species of the relatively large genus Dichorisandra, before an adequate understanding can be attained of how ontogenetic processes have evolved and shaped the remarkable floral diversity in this subtribe.

Floral anatomy of Bromeliaceae, with particular reference to the evolution of epigyny and septal nectaries in commelinid monocots

Floral anatomy is described in ten genera of Bromeliaceae, including three members of subfamily Bromelioideae, three Tillandsioideae, and four genera of the polyphyletic subfamily Pitcairnioideae (including Brocchinia, the putatively basal genus of Bromeliaceae). Bromeliaceae are probably unique in the order Poales in possessing septal nectaries and epigynous or semi-epigynous flowers. Evidence presented here from floral ontogeny, vasculature, and the relative positions of nectary and ovules indicates that there could have been one or more reversals to apparent hypogyny in Bromeliaceae, although this hypothesis requires a better-resolved phylogeny. Such evolutionary reversals probably evolved in response to specialist pollinators, and in conjunction with other aspects of floral morphology of Bromeliaceae, such as the petal appendages of some species. The ovary is initiated in an inferior position even in semi-epigynous or hypogynous species. The ovary of all so-called hypogynous Bromeliaceae is actually semi-inferior, because the septal nectary is infralocular; in these species the nectaries have a labyrinthine surface and many vascular bundles. Brocchinia differs from most other fully epigynous species in that each carpel is secretory at the apex and reproductive, rather than secretory, at the base.

Floral Ontogeny in Calliandra angustifolia (Leguminosae: Mimosoideae: Ingeae) and Its Systematic Implications

The floral ontogeny of Calliandra angustifolia, studied using SEM, shows striking differences compared with all other investigated Mimosoideae. The initiation of the sepals is unidirectional from an adaxial to abaxial position, which is a very rare character within Leguminosae. Aestivation of the calyx is cochlear descending, which is a new character within Ingeae. The synchronous initiation of the petals and their valvate aestivation are the only characters that are congruent with the other studied Mimosoideae. The initiation of the androeceum is helical, which has never been found within Mimosoideae. The early pistil development resembles that of Zapoteca, which was recently segregated from Calliandra, whereas the middle and late developmental stages differ clearly in formation of a sessile pistil without a gynophore and an expanded capitate stigma. The presented character combination is unique within Mimosoideae, and no parallels to the genus Zapoteca could be found.