What keeps the style under tension? Experimental tests to understand the biomechanics of the explosive style movement in Marantaceae.

Pollination in Marantaceae is mediated by an explosive style movement. Before release, style tension is held by the hooded staminode. When a pollinator touches the trigger appendage of the hooded staminode the latter deforms and the style rapidly curls upwards. This movement has been interpreted as a turgor movement by some authors, but recent studies clearly indicate that setup, hold and release of tension are purely mechanical processes. However, in view of the high diversity of hooded staminodes, the question arises what keeps the tension in species with very thin staminodes. To test the holding mechanisms, we conducted mechanical and physico-chemical release experiments in four species with robust and four species with thin hooded staminodes in their natural tropical environment. We found almost the same response of all species to mechanical treatments, but species-specific reactions to different physico-chemical conditions. This indicates that style release follows the same mechanical principles in all species, but that the sensitivity of the explosive movement depends on material properties like tissue thickness and turgescence. As to the holding mechanisms, we found different degrees of floral synorganization. The hood of the hooded staminode formerly interpreted as an important holding structure does not play a noteworthy role. Instead, the basal plate of the hooded staminode antagonises the pressure of the style head against the holding point of the hooded staminode in species with robust hooded staminodes and well-developed basal plates. In some species with a thin hooded staminode, the latter is closely attached to the style and most likely stabilises tension by adhesive forces. In another species, a morphologically analogous structure adopts the function of the basal plate. We conclude that the holding mechanism of the style tension diversified during the evolution of Marantaceae whereas the release mechanism itself has been conserved throughout the family.

Pseudanthia in angiosperms: a review.

BACKGROUND: Pseudanthia or 'false flowers' are multiflowered units that resemble solitary flowers in form and function. Over the last century the term 'pseudanthium' has been applied to a wide array of morphologically divergent blossoms, ranging from those with easily noticeable florets to derived, reduced units in which individual flowers become almost indistinguishable. Although initially admired mostly by botanists, the diversity and widespread distribution of pseudanthia across angiosperms has already made them a fascinating topic for evolutionary and developmental comparative studies. SCOPE: This review synthesizes historical and current concepts on the biology of pseudanthia. Our first aim is to establish a clear, operational definition of pseudanthium and disentangle common terminological misconceptions surrounding that term. Our second aim is to summarize knowledge of the morphological and developmental diversity of pseudanthia and embed it within a modern phylogenetic framework. Lastly, we want to provide a comprehensive overview on the evolution and ecological importance of pseudanthia and outline perspectives for future studies. CONCLUSIONS: The understanding of pseudanthia has changed multiple times and reflects three different interpretations of their 'flower-like' qualities: developmental (similarity in structure), figural (similarity in form and function) and phylogenetic (homology between angiosperm flowers and monoecious reproductive shoots in gymnosperms). Here, we propose to narrow the term pseudanthium to multiflowered blossoms resembling zoophilous flowers in form, i.e. in being structurally subdivided in a showy periphery and a reproductive centre. According to this definition, pseudanthia sensu stricto evolved independently in at least 41 angiosperm families. The recurrent acquisition of pseudanthia sensu stricto in all major lineages of flowering plants indicates repeated interactions between developmental constraints (smallness of flowers, meristematic conditions) and selective pressures, such as demands of pollinators and/or environmental conditions.

Rhizome architecture, development and vascularization in the water lily Nymphaea alba.

BACKGROUND AND AIMS: Water lilies are of particular interest with regard to the evolution of angiosperms. They live in an aquatic environment and have been regarded as links to the monocots by some authors. Vascular bundles are sometimes described as scattered or atactostelar as in monocots. However, this view needs to be clarified as the morphology and vascularization of Nymphaea rhizomes remain to be understood. METHODS: The rhizome of Nymphaea alba was re-investigated morphologically and histologically. Developmental studies were conducted using scanning electron microscopy. Comprehensive histological analyses, including hand and microtome sections and a variety of specific staining procedures, were conducted to re-evaluate the composition of longitudinal and transverse tissue. KEY RESULTS: The rhizome is covered by parenchymatous nodal cushions each bearing a leaf and several adventitious roots. Internodes are extremely short. The apex is flat and early overtopped by developing leaf primordia and cushions. The phyllotaxis is spiral and passes alternately through vegetative and reproductive phases. Flowers appear in the leaf spiral, and lack a subtending bract and a cushion below the peduncle. The reproductive phase includes two or three flowers which alternate with a single leaf. The rhizome is histologically subdivided into a central core, an aerenchymatic cortex, and a parenchymatic exocortex formed to a great extent by the nodal cushions. The core contains strands of vascular bundles united to a complex vascular plexus. Vascular elements continuously anastomose and change shape and direction. Provascular strands originating from leaf primordia merge with the outer core vascular tissue whereas the flower strands run into the centre of the core. Roots originating from the parenchymatous cushions show the characteristic actinostelic pattern, which changes into a collateral pattern inside the rhizome. Several root traces merge and form one strand leading to the central core. Early cell divisions below the apical meristem dislocate leaf, flower and root primordia and their provascular strands outwards. Consequently, fully developed vascular strands insert horizontally into the vascular plexus at advanced rhizome stages. CONCLUSIONS: The absence of bracts and cushions below the flowers, the alternate leaf-flower sequence and the course of the peduncle strand suggest that the rhizome is sympodially instead of monopodially organized. The spiral phyllotaxis extends in this case over several shoot orders, masking the branching pattern. The vascular strands in the central plexus differ considerably from vascular bundles in monocots, confirming the unique vascularization in Nymphaea. Sclerenchymatic bundle sheaths are lacking, and vascular bundles continuously split and anastomose throughout the rhizome. Though vascular bundles in petioles and peduncles of N. alba show similarities with some Alismatales, the vascular system of N. alba in general has little in common with that of monocots.

The Search for Common Origin: Homology Revisited.

Understanding the evolution of biodiversity on Earth is a central aim in biology. Currently, various disciplines of science contribute to unravel evolution at all levels of life, from individual organisms to species and higher ranks, using different approaches and specific terminologies. The search for common origin, traditionally called homology, is a connecting paradigm of all studies related to evolution. However, it is not always sufficiently taken into account that defining homology depends on the hierarchical level studied (organism, population, and species), which can cause confusion. Therefore, we propose a framework to define homologies making use of existing terms, which refer to homology in different fields, but restricting them to an unambiguous meaning and a particular hierarchical level. We propose to use the overarching term "homology" only when "morphological homology," "vertical gene transfer," and "phylogenetic homology" are confirmed. Consequently, neither phylogenetic nor morphological homology is equal to homology. This article is intended for readers with different research backgrounds. We challenge their traditional approaches, inviting them to consider the proposed framework and offering them a new perspective for their own research.

Sex-differential reproduction success and selection on floral traits in gynodioecious Salvia pratensis.

BACKGROUND: Gynodioecy, a sexual system with hermaphrodite and female individuals in a population, raises the question how the two sexual morphs are maintained. Salvia pratensis is a gynodioecious species featured by its modified stamens that act as a lever mechanism in pollination. Given sexual dimorphism in floral traits of the species, it is predictable that two sexual morphs differ in their interplay with pollinators and thus in their fitness. In this study, we investigated sex-specific reproduction success and floral adaptation in a population of S. pratensis. RESULTS: We found that two sexual morphs in S. pratensis distinctly differed in their floral proportions. Female flowers fitted better to the pollinators than hermaphrodites in terms of touching the stigmas when being probed, and hence were more efficient in pollen deposition. Floral traits overall underwent stronger selection in the population, with stigma position and corolla length subject to disruptive selection mediated by different body-sized bumble bees; some selections on floral traits were significantly different in the strength, even opposite in the direction between two morphs. Flower production tended to be under correlational selection with floral structural traits, implying that a large plant with many flowers did not show an advantage in fitness unless its flower construction mechanically matched the pollinators well. CONCLUSIONS: In conclusion, the pollinator-mediated selection likely played an important role in the evolution and maintenance of sexual dimorphism in the gynodioecious S. pratensis; and sex-divergent mechanical interaction with pollinators served as a critical mechanism by which female individuals were maintained in the population with a female advantage in pollen deposition efficiency (i.e. receiving pollen).

Flower-like heads from flower-like meristems: pseudanthium development in Davidia involucrata (Nyssaceae).

Flower-like inflorescences (pseudanthia) have fascinated botanists for a long time. They are explained as condensed inflorescences implying that the pseudanthium develops from an inflorescence meristem (IM). However, recent developmental studies identified a new form of reproductive meristem, the floral unit meristem (FUM). It differs from IMs by lacking acropetal growth and shares fractionation, expansion and autonomous space filling with flower meristems (FM). The similarity among FUMs and FMs raises the question how far flower-like heads originate from flower-like meristems. In the present paper, pseudanthium development in Davidia involucrata is investigated using scanning electron microscopy. D. involucrata has pincushion-shaped heads composed of densely aggregated, perianthless flowers and associated with two large showy bracts. Early developmental stages show a huge naked FUM. The FMs appear almost simultaneously and lack subtending bracts. With ongoing FUM expansion new space is generated which is immediately used by further FM fractionation. The heads have only staminate flowers or are andromonoecious with staminate and a single perfect flower in oblique position. All FMs lack perianth structures and fractionate a variable number of stamen primordia. The perfect FM is much larger than the staminate FMs and forms a syncarpous gynoecium with inferior ovary. Pseudanthium development in D. involucrata confirms the morphogenetic similarity to FMs as to acropetal growth limitation, meristem expansion and fractionation. It thus should not be interpreted as a condensed inflorescence, but as a flower equivalent. Furthermore as the FUM develops inside a bud, its development is considered to be influenced by mechanical pressure. The oblique position of the perfect flower, the developmental delay of the proximal flowers, and the variable number of stamens which were observed in the pseudanthium development, can be caused by mechanical pressure. Next to the Asteraceae, D. involucrata offers a further example of a pseudanthium originating from a FUM. More knowledge on FUMs is still needed to understand diversification and evolution of flower-like inflorescences.

Time to split Salvia s.l. (Lamiaceae) - New insights from Old World Salvia phylogeny.

AIMS: Salvia L. is widely known as the largest genus in the mint family. A morphological modification of the androecium (lever-like stamens) was used to support this genus. However, molecular data revealed that Salvia is polyphyletic. Since phylogenetic studies largely underrepresented Old World Salvia species, we filled this gap and combined new data with existing sequences. The aim of our study was the identification of well-supported clades that provide the basis for evolutionary and taxonomic conclusions. METHODS: We included ITS data (internal transcribed spacer) from 220 Salvia species, 86 of which were sequenced for the first time. Additionally, the highly variable plastid marker rpl32-trnL was sequenced, providing new data for 100 Salvia species. These sequences were combined with the accessions available from GenBank. Old World Salvia is represented herein with 57% of its species. The two datasets were analyzed separately using BI and ML approaches. RESULTS: Our data confirm that Salvia is polyphyletic with four distinct evolutionary lineages (Clade I-IV), including five additional genera. The clades strongly reflect the geographical distribution, i.e., Clade IV (East Asia), Clade III (Southwest Asia to Northern Africa), and Clade II (America). The origin of Salvia s.s. (Clade I) is most likely Southwest Asia. A high degree of parallel character evolution was identified in most of the Old World sections. Based on our results, we reconstructed the evolution and biogeography of Salvia s.l. and propose to split this large group into six genera, each supported by geographical distribution, morphology, and karyology. CONCLUSION: Salvia s.l. is a polyphyletic group that was originally regarded as a genus because its species share a derived stamen structure. However, phylogenetic data clearly indicate that this floral trait and other morphological characters evolved in parallel. Our study illustrates that the combination of different data sets allows a comprehensive reconstruction of taxa and characteristic evolution, both of which are a precondition for future revision.

Space matters: meristem expansion triggers corona formation in Passiflora.

BACKGROUND AND AIMS: Flower meristems differ from vegetative meristems in various aspects. One characteristic is the capacity for ongoing meristem expansion providing space for new structures. Here, corona formation in four species of Passiflora is investigated to understand the spatio-temporal conditions of its formation and to clarify homology of the corona elements. METHODS: One bird-pollinated species with a single-rowed tubular corona (Passiflora tulae) and three insect-pollinated species with three (P. standleyi Killip), four (P. foetida L. 'Sanctae Martae') and six (P. foetida L. var. hispida) ray-shaped corona rows are chosen as representative examples for the study. Flower development is documented by scanning electron microscopy. Meristem expansion is reconstructed by morphometric data and correlated with the sequential corona element formation. KEY RESULTS: In all species, corona formation starts late in ontogeny after all floral organs have been initiated. It is closely correlated with meristem expansion. The rows appear with increasing space in centripetal or convergent sequence. CONCLUSIONS: Based on the concept of fractionation, space induces primordia formation which is a self-regulating process filling the space completely. Correspondingly, the corona is interpreted as a structure of its own, originating from the receptacle. Considering the principle capacity of flower meristems to generate novel structures widens the view and allows new interpretations in combination with molecular, phylogenetic and morphogenetic data.

Why Africa matters: evolution of Old World Salvia (Lamiaceae) in Africa.

BACKGROUND AND AIMS: Salvia is the largest genus in Lamiaceae and it has recently been found to be non-monophyletic. Molecular data on Old World Salvia are largely lacking. In this study, we present data concerning Salvia in Africa. The focus is on the colonization of the continent, character evolution and the switch of pollination systems in the genus. METHODS: Maximum likelihood and Bayesian inference were used for phylogenetic reconstruction. Analyses were based on two nuclear markers [internal transcribed spacer (ITS) and external transcribed spacer (ETS)] and one plastid marker (rpl32-trnL). Sequence data were generated for 41 of the 62 African taxa (66 %). Mesquite was used to reconstruct ancestral character states for distribution, life form, calyx shape, stamen type and pollination syndrome. KEY RESULTS: Salvia in Africa is non-monophyletic. Each of the five major regions in Africa, except Madagascar, was colonized at least twice, and floristic links between North African, south-west Asian and European species are strongly supported. The large radiation in Sub-Saharan Africa (23 species) can be traced back to dispersal from North Africa via East Africa to the Cape Region. Adaptation to bird pollination in southern Africa and Madagascar reflects parallel evolution. CONCLUSIONS: The phenotypic diversity in African Salvia is associated with repeated introductions to the continent. Many important evolutionary processes, such as colonization, adaptation, parallelism and character transformation, are reflected in this comparatively small group. The data presented in this study can help to understand the evolution of Salvia sensu lato and other large genera.

Flies as pollinators of melittophilous Salvia species (Lamiaceae).

UNLABELLED: • PREMISE OF THE STUDY: Floral adaptation to a functional pollinator group does not necessarily mean close specialization to a few pollinator species. For the more than 950 species of Salvia, only bee and bird pollinations are known. Restriction to these pollinators is mainly due to the specific flower construction (lever mechanism). Nevertheless, it has been repeatedly suggested that Salvia flowers might also be pollinated by flies. Are flies able to handle the lever mechanism? Are they functionally equivalent pollinators? In this study, we compared and quantified pollen transfer by bees and flies to test whether flies are true pollinators in Salvia.• METHODS: We identified pollinators using field observations and photos. Video documentation of the visitation rate and the site of pollen placement on the pollinator body, morphometric measurements, quantification of pollen placement, pollen load, handling time, and stigma contact ratio were analyzed.• KEY RESULTS: Field investigations revealed that 19 insect species pollinated S. virgata and four pollinated S. verticillata, including 16 bee species from seven genera of the Apidae and three fly species from three genera of the Nemestrinidae and Tabanidae.• CONCLUSIONS: Flies have been found to be pollinators in primarily bee-pollinated Salvia species. This result demonstrates the potential of a given "melittoid" flower construction to broaden the range of pollinators to guarantee successful pollination and seed production. Though bees, particularly Bombus terrestris, were more efficient than flies, the study shows that flies significantly contribute to pollen transfer in Salvia.

Lack of pollinators selects for increased selfing, restricted gene flow and resource allocation in the rare Mediterranean sage Salvia brachyodon.

Range contraction and habitat fragmentation can cause biodiversity loss by creating conditions that directly or indirectly affect the survival of plant populations. Fragmented habitats can alter pollinator guilds and impact their behavior, which may result in pollen/pollinator limitation and selection for increased selfing as a mechanism for reproductive assurance. We used Salvia brachyodon, a narrowly distributed and endangered sage from eastern Adriatic, to test the consequences of range contraction and habitat fragmentation. Molecular data indicate a severe and relatively recent species range reduction. While one population is reproductively almost completely isolated, moderate gene flow has been detected between the remaining two populations. The high pollen-to-ovule ratio and the results of controlled hand pollination indicate that S. brachyodon has a mixed mating system. Quantitative and qualitative differences in the community and behaviour of flower visitors resulted in limited pollination services in one population where no effective pollinator other than pollen and nectar robbers were observed. In this population, self-pollination predominated over cross-pollination. Various environmental factors, in which plant-pollinator interactions play a pivotal role, have likely created selection pressures that have led to genetic and phenotypic differentiation and different resource allocation strategies among populations.

Towards an ontogenetic understanding of inflorescence diversity.

BACKGROUNDS AND AIMS: Conceptual and terminological conflicts in inflorescence morphology indicate a lack of understanding of the phenotypic diversity of inflorescences. In this study, an ontogeny-based inflorescence concept is presented considering different meristem types and developmental pathways. By going back to the ontogenetic origin, diversity is reduced to a limited number of types and terms. METHODS: Species from 105 genera in 52 angiosperm families are investigated to identify their specific reproductive meristems and developmental pathways. Based on these studies, long-term experience with inflorescences and literature research, a conceptual framework for the understanding of inflorescences is presented. KEY RESULTS: Ontogeny reveals that reproductive systems traditionally called inflorescences fall into three groups, i.e. 'flowering shoot systems' (FSS), 'inflorescences' sensu stricto and 'floral units' (FUs). Our concept is, first, based on the identification of reproductive meristem position and developmental potential. The FSS, defined as a seasonal growth unit, is used as a reference framework. As the FSS is a leafy shoot system bearing reproductive units, foliage and flowering sequence play an important role. Second, the identification of two different flower-producing meristems is essential. While 'inflorescence meristems' (IMs) share acropetal primordia production with vegetative meristems, 'floral unit meristems' (FUMs) resemble flower meristems in being indeterminate. IMs produce the basic inflorescence types, i.e. compound and simple racemes, panicles and botryoids. FUMs give rise to dense, often flower-like units (e.g. heads). They occur solitarily at the FSS or occupy flower positions in inflorescences, rendering the latter thyrses in the case of cymose branching. CONCLUSIONS: The ontogenetic concept differs from all existing inflorescence concepts in being based on meristems and developmental processes. It includes clear terms and allows homology statements. Transitional forms are an explicit part of the concept, illustrating the ontogenetic potential for character transformation in evolution.

Testing the ontogenetic base for the transient model of inflorescence development.

BACKGROUNDS AND AIMS: Current research in plant science has concentrated on revealing ontogenetic processes of key attributes in plant evolution. One recently discussed model is the 'transient model' successful in explaining some types of inflorescence architectures based on two main principles: the decline of the so called 'vegetativeness' (veg) factor and the transient nature of apical meristems in developing inflorescences. This study examines whether both principles find a concrete ontogenetic correlate in inflorescence development. METHODS: To test the ontogenetic base of veg decline and the transient character of apical meristems the ontogeny of meristematic size in developing inflorescences was investigated under scanning electron microscopy. Early and late inflorescence meristems were measured and compared during inflorescence development in 13 eudicot species from 11 families. KEY RESULTS: The initial size of the inflorescence meristem in closed inflorescences correlates with the number of nodes in the mature inflorescence. Conjunct compound inflorescences (panicles) show a constant decrease of meristematic size from early to late inflorescence meristems, while disjunct compound inflorescences present an enlargement by merging from early inflorescence meristems to late inflorescence meristems, implying a qualitative change of the apical meristems during ontogeny. CONCLUSIONS: Partial confirmation was found for the transient model for inflorescence architecture in the ontogeny: the initial size of the apical meristem in closed inflorescences is consistent with the postulated veg decline mechanism regulating the size of the inflorescence. However, the observed biphasic kinetics of the development of the apical meristem in compound racemes offers the primary explanation for their disjunct morphology, contrary to the putative exclusive transient mechanism in lateral axes as expected by the model.

Andromonoecy and developmental plasticity in Chaerophyllum bulbosum (Apiaceae-Apioideae).

BACKGROUND AND AIMS: Andromonoecy, the presence of hermaphrodite and male flowers in the same individual, is genetically fixed or induced, e.g. by fruit set. Little is known about the forces triggering andromonoecy in the Apiaceae. In the present study, a natural population of the protandrous Chaerophyllum bulbosum was investigated to elucidate architectural constraints and effects of resource reallocation. METHODS: Three sets of plants (each n = 15) were treated by hand pollination, pollinator exclusion and removal of low-order inflorescences. Fifteen untreated plants were left as controls. KEY RESULTS: Untreated plants produce umbels up to the third branch order, with increasing proportions of male flowers from 15 % (terminal umbel) to 100 % (third-order umbels). Fruit set correspondingly decreases from 70% (terminal umbel) to <10 % (second-order umbels). Insignificant differences from hand-pollinated plants do not reveal any sign of pollinator limitation at the study site. Bagged individuals show the same increase in male flowers with age as untreated plants, indicating that the presence of andromonoecy is not induced by fruit set. After umbel removal, individuals tend to present a higher number of hermaphrodite flowers and fruits in the umbels of second and third order. Three plants (25 %) produced an additional branch order composed of 100 % male umbels. CONCLUSIONS: Inherited andromonoecy and the plastic response to environmental conditions are interpreted as a self-regulating system saving investment costs and optimizing fruit set at the same time.

Inflorescences: concepts, function, development and evolution.

BACKGROUND: Inflorescences are complex structures with many functions. At anthesis they present the flowers in ways that allow for the transfer of pollen and optimization of the plant's reproductive success. During flower and fruit development they provide nutrients to the developing flowers and fruits. At fruit maturity they support the fruits prior to dispersal, and facilitate effective fruit and seed dispersal. From a structural point of view, inflorescences have played important roles in systematic and phylogenetic studies. As functional units they facilitate reproduction, and are largely shaped by natural selection. SCOPE: The papers in this Special Issue bridge the gap between structural and functional approaches to inflorescence evolution. They include a literature review of inflorescence function, an experimental study of inflorescences as essential contributors to the display of flowers, and two papers that present new methods and concepts for understanding inflorescence diversity and for dealing with terminological problems. The transient model of inflorescence development is evaluated in an ontogenetic study, and partially supported. Four papers present morphological and ontogenetic studies of inflorescence development in monophyletic groups, and two of these evaluate the usefulness of Hofmeister's Rule and inhibitory fields to predict inflorescence structure. In the final two papers, Bayesian and Monte-Carlo methods are used to elucidate inflorescence evolution in the Panicoid grasses, and a candidate gene approach is used in an attempt to understand the evolutionary genetics of inflorescence evolution in the genus Cornus (Cornaceae). Taken as a whole, the papers in this issue provide a glimpse of contemporary approaches to the study of the structure, development, and evolution of inflorescences, and suggest fruitful new directions for research.

Dark-centred umbels in Apiaceae: diversity, development and evolution.

The wild carrot (Daucus carota) is famous for its dark flowers in the umbel centre. Several studies have been conducted to figure out their functional significance, but the evolution of the dark centre remains an enigma. In the present paper, we consider all known apioid species with dark-centred umbels to get a deeper understanding of their biology and evolution. Based on herbaria studies, literature and field work, we reconstructed the distribution area of 10 species (7 genera, 6 clades) of Apiaceae-Apioideae. To recognize homology of the dark structures, developmental studies were conducted in Artedia squamata and Echiophora trichophylla Field studies included architecture, flower morph distribution (andromonoecy) and flowering sequence within the plants, abundancy and behaviour of umbel visitors and preliminary manipulation experiments (removal/adding of dark structures). The dark structures are not homologous to each other. In the Daucus alliance, central flowers or umbellets are conspicuous, whereas in other species dark brush-like (A. squamata) or club-shaped structures (Dicyclophora persica, Echinophora trichophylla, Tordylium aegyptiacum, T. cappadocicum) develop from a naked receptacle. Species are andromonoecious, have a modular architecture and flower in multicyclic protandrous sequence. Among the many umbel visitors, beetles were the most abundant group. Only visitors found on umbels in both flowering phases were recognized as possible pollinators. Manipulation experiments indicated that the dark structures influence the behaviour of some, but not all umbel visitors. In Echinophora trichophylla, a massive gall infection was observed. It is evident that the dark structures evolved several times in parallel. The brush- and club-shaped structures are interpreted as the results of mutations affecting umbel development. Dark umbel centres are most likely stabilized by selection due to their general adaptive function. Their appearance in an area known as a hotspot of beetle pollination gives rise to the assumption that they may act as beetle marks.

Flower-like meristem conditions and spatial constraints shape architecture of floral pseudanthia in Apioideae.

BACKGROUND: Pseudanthia are multiflowered units that resemble single flowers, frequently by association with pseudocorollas formed by enlarged peripheral florets (ray flowers). Such resemblance is not only superficial, because numerous pseudanthia originate from peculiar reproductive meristems with flower-like characteristics, i.e. floral unit meristems (FUMs). Complex FUM-derived pseudanthia with ray flowers are especially common in Apiaceae, but our knowledge about their patterning is limited. In this paper, we aimed to investigate both the genetic and morphological basis of their development. RESULTS: We analysed umbel morphogenesis with SEM in six species representing four clades of Apiaceae subfamily Apioideae with independently acquired floral pseudanthia. Additionally, using in situ hybridization, we investigated expression patterns of LEAFY (LFY), UNUSUAL FLORAL ORGANS (UFO), and CYCLOIDEA (CYC) during umbel development in carrot (Daucus carota subsp. carota). Here, we show that initial differences in size and shape of umbel meristems influence the position of ray flower formation, whereas an interplay between peripheral promotion and spatial constraints in umbellet meristems take part in the establishment of specific patterns of zygomorphy in ray flowers of Apiaceae. This space-dependent patterning results from flower-like morphogenetic traits of the umbel which are also visible at the molecular level. Transcripts of DcLFY are uniformly distributed in the incipient umbel, umbellet and flower meristems, while DcCYC shows divergent expression in central and peripheral florets. CONCLUSIONS: Our results indicate that umbels develop from determinate reproductive meristems with flower-like characteristics, which supports their recognition as floral units. The great architectural diversity and complexity of pseudanthia in Apiaceae can be explained by the unique conditions of FUMs-an interplay between expression of regulatory genes, specific spatio-temporal ontogenetic constraints and morphogenetic gradients arising during expansion and repetitive fractionation. Alongside Asteraceae, umbellifers constitute an interesting model for investigation of patterning in complex pseudanthia.

Consistent phenological shifts in the making of a biodiversity hotspot: the Cape flora.

BACKGROUND: The best documented survival responses of organisms to past climate change on short (glacial-interglacial) timescales are distributional shifts. Despite ample evidence on such timescales for local adaptations of populations at specific sites, the long-term impacts of such changes on evolutionary significant units in response to past climatic change have been little documented. Here we use phylogenies to reconstruct changes in distribution and flowering ecology of the Cape flora--South Africa's biodiversity hotspot--through a period of past (Neogene and Quaternary) changes in the seasonality of rainfall over a timescale of several million years. RESULTS: Forty-three distributional and phenological shifts consistent with past climatic change occur across the flora, and a comparable number of clades underwent adaptive changes in their flowering phenology (9 clades; half of the clades investigated) as underwent distributional shifts (12 clades; two thirds of the clades investigated). Of extant Cape angiosperm species, 14-41% have been contributed by lineages that show distributional shifts consistent with past climate change, yet a similar proportion (14-55%) arose from lineages that shifted flowering phenology. CONCLUSIONS: Adaptive changes in ecology at the scale we uncover in the Cape and consistent with past climatic change have not been documented for other floras. Shifts in climate tolerance appear to have been more important in this flora than is currently appreciated, and lineages that underwent such shifts went on to contribute a high proportion of the flora's extant species diversity. That shifts in phenology, on an evolutionary timescale and on such a scale, have not yet been detected for other floras is likely a result of the method used; shifts in flowering phenology cannot be detected in the fossil record.

Open and closed inflorescences: more than simple opposites.

The absence of a terminal flower in inflorescences ('open inflorescences') is currently explained by the maintenance of putative stem-cells in the central zone (CZ) of the inflorescence meristem (IM) governed by the CLAVATA-WUSCHEL regulatory loop. Disruption of this regulatory pathway, as in Arabidopsis TERMINAL FLOWER LOCUS 1 mutants, leads to terminal flower production. However, recent studies in other taxa reveal novel mechanisms of inflorescence termination; for example, the SEPALLATA-like MADS-box floral identity gene GERBERA REGULATOR OF CAPITULUM DEVELOPMENT 2 in Gerbera excludes the retention of a CZ as an ontogenetic cause for the openness of these inflorescences. Moreover, comparative histological studies show that the retention of a CZ in the IM, mostly a feature of the 'typical open families', is absent in open inflorescences of other families. Concerning these groups, new evidence suggests that spatial constraints at the IM could play a role at the time when terminal flower production (or not) is determined. This indicates that the multiple loss and re-gain of the terminal flower in angiosperms is necessarily based on more than one ontogenetic pathway.

Functional implications of the staminal lever mechanism in Salvia cyclostegia (Lamiaceae).

BACKGROUND AND AIMS: Flower morphology and inflorescence architecture affect pollinator foraging behaviour and thereby influence the process of pollination and the reproductive success of plants. This study explored possible ecological functions of the lever-like stamens and the floral design in Salvia cyclostegia. METHODS: Flower construction was experimentally manipulated by removing either the lower lever arms or the upper fertile thecae of the two stamens from a flower. The two types of manipulated individuals were intermixed with the control ones and randomly distributed in the population. KEY RESULTS: Removing the sterile lower lever arms significantly reduced handling time per flower of the main pollinator, Bombus personatus. Interestingly, this manipulation did not increase the number of flowers probed per plant visit, but instead reduced it, i.e. shortened the visit sequence of the bumble-bees. Both loss of staminal lever function by removing lower lever arms and exclusion of self pollen by removing upper fertile thecae significantly reduced seed set per flower and seed set per plant. Both the manipulations interacted significantly with inflorescence size for the effect on female reproductive output. CONCLUSIONS: Though the intact flowers demand a long handling time for pollinators, the reversible staminal lever is of advantage by promoting dispersal of pollen and thus the male function. The particular floral design in S. cyclostegia contributes to the floral constancy of B. personatus bumble-bees, with the lower lever arms acting as an optical cue for foraging cognition.