Inflorescence structure in species of Spartina Schreb. (Poaceae: Chloridoideae: Cynodonteae)

The typology developed by Troll was followed to describe inflorescence structures for 15 species of Spartina. In all species here studied, truncation of the terminal spikelet of the main axis and primary paracladium was observed. The truncation can also involve the short paracladia subzone so that the inflorescence is confined to just the long paracladia subzone. A great homogenization of paracladia and maximum ramification degree limited generally to the second order of branching are distinctive characteristics of the genus. Proximal paracladia with third-order branching were found in only three specimens, and in these exceptional cases, the homogenization is partial. Sometimes, in some species, a subzone of long and short paracladia can be distinguished. The absence of trophotagma paracladia in all the species studied was verified. The variation in the structure of the inflorescence among species is due to the differences in the number of short paracladia, long paracladia, total number of primary paracladia and also in the angle of divergence of the long paracladia from the main axis. The latter, in addition to variations in the intercalary growth of the internodes produces modifications in the general appearance of the inflorescences. The systematic and taxonomic value of the inflorescences in Spartina is discussed.     

Inflorescence structure in species of Scleria subgenus Hypoporum and subgenus Scleria (Sclerieae-Cyperaceae)

The objective of this study was to realize a typology approach toward the inflorescences in Scleria in order to provide characters that would have potential use in further taxonomic and phylogenetic research and that would allow identification of the tendencies and processes that could have yielded the variations within Scleria inflorescences. The majority of species studied present a main florescence; Scleria reticularis and S. melanomphala have truncated inflorescences. The variations are related to the grade of development reached by the main florescence and the different parts of the paracladial zone. Major inflorescence variability was found in section Scleria. A change in spikelet sexuality can occur toward the distal parts. There were variations in the distinct species with respect to the hierarchy of the paracladia where the change occurs. Future investigations should center on the ontogenetic aspects of inflorescence development of Scleria, integrating these results, together with those of adult inflorescences, into taxonomic and phylogenetic investigations.     

Inflorescence structure in Rhynchospora Vahl (Cyperaceae)

We investigated the inflorescence structure of Rhynchospora following the methodology and terminology of Troll's school, with the objective of providing a characterization of the inflorescence suitable to evaluate the processes responsible for the diversity observed. Homogenization of inflorescence structures may occur fully or partially. In the first case, all branches of the inflorescence are homogeneous, while in the later, distal and proximal parts of the inflorescence bear homogeneous branches, but in the middle portions of the inflorescence non-homogeneous branches exist. Other characters leading to different forms of inflorescences are branching degree, internode elongation along the main axis of the synflorescence, degree of epipodium elongation of distal paraclades, development of bract and prophyll, and development of prophyllar paraclades. We identified three main types of inflorescences: (1) partially homogeneous paniculodia, (2) partially homogeneous capitate heads, and (3) a fully homogeneous capitate head. Within the first type, four subtypes were also recognized. Finally, we discuss how these processes can operate to produce the variation of the inflorescence shape.     

Morphology and anatomy of inflorescence and inflorescence axis in Paepalanthus sect. Diphyomene Ruhland (Eriocaulaceae,Poales) and its taxonomic implications

Paepalanthus sect. Diphyomene has inflorescences arranged in umbels. The underlying bauplan seems however to be more complex and composed of several distinct subunits. Despite appearing superficially very similar, the morphology and anatomy of the inflorescences can supply useful information for the understanding of the phylogeny and taxonomy of the group. Inflorescences of Paepalanthus erectifolius, Paepalanthus flaccidus, Paepalanthus giganteus, and Paepalanthus polycladus were analyzed in regard to branching pattern and anatomy. In P. erectifolius, P. giganteus and P. polycladus the structure is a tribotryum, with terminal dibotryum, and with pherophylls bearing lateral dibotrya. In P. flaccidus, the inflorescence is a pleiobotryum, with terminal subunit, and without pherophylls. Secondary inflorescences may occur in all species without regular pattern. Especially when grown in sites without a pronounced seasonality, the distinction between enrichment zone (part of the same inflorescence) and new inflorescences may be obscured. The main anatomical features supplying diagnostic and phylogenetic information are as follows: (a) in the elongated axis, the thickness of the epidermal cell walls and the cortex size; (b) in the bracts, the quantity of parenchyma cells (c) in the scapes, the shape and the presence of a pith tissue. Therefore, P. sect. Diphyomene can be divided in two groups; group A is represented by P. erectifolius, P. giganteus and P. polycladus, and group B is represented by P. flaccidus. The differentiation is based in both, inflorescence structure and anatomy. Group A presents a life cycle and anatomical features similar to species of Actinocephalus. Molecular trees also point that these two groups are closely related. However, inflorescence morphology and blooming sequence are different. Species of group B present an inflorescence structure and anatomical features shared with many genera and species in Eriocaulaceae. The available molecular and morphology based phylogenies still do not allow a precise allocation of the group in the bulk of basal species of Paepalanthus collocated in P. sect. Variabiles. The characters described and used here supply however important information towards this goal.     

MORPHOLOGY,EVOLUTION, AND TAXONOMIC SIGNIFICANCE OF THE INFLORESCENCE IN CORDYLANTHUS (SCROPHULARIACEAE)

The genus Cordyhmthus has considerable diversity in its inflorescences while the other genera of tribe Rhinantheae (Scrophulariaceae) uniformly have racemes or spikes. Four distinct inflorescence types are recognized and their homologies and evolutionary history are postulated. Thus it is suggested that the basic florescence type, the elongated spike (Type I), has undergone evolutionary reduction to a few-flowered spike and ultimately to a single-flowered florescence (Type II). Further evolution involving processes of compaction and clustering of the single-flowered florescences has resulted in glomerulate clusters (Type III) and spiciform clusters (Type IV). Knowledge of inflorescence homologies and distribution of the four inflorescence types in the genus has been of considerable aid in formulating a new infrageneric classification. Using evidence primarily from inflorescence, floral, and seed morphology, as well as from geographical distribution and ecology, a classification is proposed establishing three subgenera, namely subg. Dicranostegia, subg. Hemistegia, and subg. Cordylanthus, the last with three sections, sect. Cordylanthus, sect. Anisocheila, and sect. Ramosi.     

Diversity of inflorescences in the Boutelouinae subtribe (Poaceae: Chloridoideae: Cynodonteae)

The Boutelouinae subtribe is comprised of one monophyletic genus, Bouteloua, with 57 species inhabiting the semi-arid regions of the New World. The inflorescences show significant structural variations, which provides an interesting system to examine their morphological evolution and identify characters and processes that may help to understand the group systematics. The structure of inflorescences was studied in 25 species of Bouteloua. All the species covered under this study have truncated polytelic inflorescences. Structural variations in the inflorescence unit among species may be accounted for by: (1) symmetry of the inflorescence unit, (2) total number of long primary branches, (3) total number of spikelets per branch, (4) number of perfect flowers per spikelet, (5) number of rudimentary flowers, and (6) reproductive system. Homogenization and truncation processes account for the diversity of mature inflorescences that exists in Bouteloua. In this work, we discuss the systematic and taxonomic value of the inflorescence in the Boutelouinae subtribe.     

The branching of the inflorescence and vegetative shoot and taxonomy of the genusKummerowia (Leguminosae)

A study of the branching of the inflorescence and the vegetative shoot of the genusKummerowia, consisting ofK. stipulacea (Maxim.) Makino andK. striata (Thunb.) Schindler, has led to the following conclusions: (1) the inflorescences of both species are reduced compound cymes, (2) the branching system of the inflorescence ofKummerowia is not clearly different from that of the vegetative shoot and there are some transitional forms between both systems, and (3) the inflorescence ofKummerowia is different from the racemose inflorescences ofLespedeza andCampylotropis. Based on the differences found in the branching system of the inflorescence,Kummerowia is distinctly separated fromLespedeza andCampylotropis and is more correctly treated as a distinct genus from the latter two.     

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.     

Defining the limits of flowers: the challenge of distinguishing between the evolutionary products of simple versus compound strobili

Recent phylogenetic reconstructions suggest that axially condensed flower-like structures evolved iteratively in seed plants from either simple or compound strobili. The simple-strobilus model of flower evolution, widely applied to the angiosperm flower, interprets the inflorescence as a compound strobilus. The conifer cone and the gnetalean ‘flower’ are commonly interpreted as having evolved from a compound strobilus by extreme condensation and (at least in the case of male conifer cones) elimination of some structures present in the presumed ancestral compound strobilus. These two hypotheses have profoundly different implications for reconstructing the evolution of developmental genetic mechanisms in seed plants. If different flower-like structures evolved independently, there should intuitively be little commonality of patterning genes. However, reproductive units of some early-divergent angiosperms, including the extant genus Trithuria (Hydatellaceae) and the extinct genus Archaefructus (Archaefructaceae), apparently combine features considered typical of flowers and inflorescences. We re-evaluate several disparate strands of comparative data to explore whether flower-like structures could have arisen by co-option of flower-expressed patterning genes into independently evolved condensed inflorescences, or vice versa. We discuss the evolution of the inflorescence in both gymnosperms and angiosperms, emphasising the roles of heterotopy in dictating gender expression and heterochrony in permitting internodal compression.     

Morphological traffic between the inflorescence and the vegetative shoot in helobial monocotyledons

Previous studies of reproductive structures in the helobial monocotyledons (Alismatidae) indicate that partitioning between flower and inflorescence is not always clear (e.g.,Lilaea,Scheuchzeria) and that this may be the result of ancestral, unisexual modules coming together to form flowers and/or inflorescences. Later evolutionary changes may have included the inflorescence becoming involved or mixed in with vegetative growth. Substitution of vegetative buds for flowers is the simplest version, and there can be additional modifications to the growth behavior of the inflorescence, such as horizontal growth and dorsiventrality. In the Alismataceae and Limnocharitaceae the derivation of stolonlike structures from inflorescences is obvious: vegetative features have been incorporated into structures that are recognizably inflorescences. In the Hydrocharitaceae the interrelationships between the inflorescence and the vegetative body are much less well defined. We previously suggested forHydrocharis, where a single axillary complex can contain both inflorescence and stolons, that the stolon is basically a sterilized inflorescence and that features of the inflorescence have become incorporated into the vegetative body. Here we will explore this theme further for the Hydrocharitaceae, using information from within and outside the family.     

Inflorescence morphology of some South American Anacardiaceae and the possible phylogenetic trends

Barfod, A. 1988. Inflorescence morphology of some South American Anacardiaceae and the possible phylogenetic trends. - Nord. J. Bot. 8: 3–11. Copenhagen. ISSN 0107–055X.
The inflorescences of 15 native and one introduced species of South American Anacardiaceae belonging to the genera Anacardium, Loxopterygium, Mangifera, Mauria, Mosquitoxylon, Schinus, Spondias, Tapirira and Toxicodendron are described according to the terminology of Troll and coworkers. The tribal divisions in the Anacardiaceae are supported by the inflorescence morphology. Tribe Spondia-deae has paniculate inflorescences whereas tribe Anacardieae and tribe Rhoeae both have thyrsoids. Toxicodendron is exceptional for the tribe Rhoeae having axillary panicles. Thyrosids are hypothesized derived from panicles by a two step process including neoteny and enriching by cymose branching.     

Papilionoid inflorescences revisited (Leguminosae-Papilionoideae)

Background and Aims

The inflorescence structure determines the spatiotemporal arrangement of the flowers during anthesis and is therefore vital for reproductive success. The Leguminosae are among the largest angiosperm plant families and they include some important crop plants. In papilionoid legumes, the raceme is the most common type of inflorescence. However, a range of other inflorescence types have evolved via various developmental processes. A (re-)investigation of inflorescences in Swainsona formosa, Cicer arietinum, Abrus precatorius, Hardenbergia violacea and Kennedia nigricans leads to new insights into reduction mechanisms and to a new hypothesis on the evolution of the papilionoid pseudoraceme.

Methods

Inflorescence morphology and ontogeny were studied using scanning electron microscopy (SEM).

Key Results

The inflorescence in S. formosa is an umbel with a rare type of pendulum symmetry which may be triggered by the subtending leaf. Inflorescences in C. arietinum are reduced to a single flower. An early formed adaxial bulge is the sterile apex of the inflorescence (i.e. the inflorescence is open and not terminated by a flower). In partial inflorescences of A. precatorius, the axis is reduced and its meristem is relocated towards the main inflorescence. Flower initiation follows a peculiar pendulum pattern. Partial inflorescences in H. violacea and in K. nigricans show reduction tendencies. In both taxa, initiated but early reduced bracteoles are present.

Conclusions

Pendulum symmetry in S. formosa is probably associated with distichous phyllotaxis. In C. arietinum, strong reduction tendencies are revealed. Based on studies of A. precatorius, the papilionoid pseudoraceme is reinterpreted as a compound raceme with condensed lateral axes. From an Abrus-like inflorescence, other types can be derived via reduction of flower number and synchronization of flower development. A plea is made for uniform usage of inflorescence terminology.Key words: Abrus precatorius, Cicer arietinum, Hardenbergia violacea, Kennedia nigricans, inflorescence, Leguminosae, Papilionoideae, pseudoraceme, Swainsona formosa     

What makes a fig: insights from a comparative analysis of inflorescence morphogenesis in Moraceae

Background and AimsMoraceae, the family of mulberry and fig trees, displays small homogeneous flowers but extremely diverse inflorescences ranging from simple and branched to complex and condensed. Inflorescences also vary in flower organization in the receptacle, in the degree of flower condensation and in receptacle shape. Thus, the objective of the present study was to compare the inflorescence morphogenesis of Moraceae species, to investigate whether clades with a similar pollination mode share the same patterns of inflorescence development and the developmental stages at which we observe the key changes resulting in the diversified inflorescence architecture that culminates in the Ficus syconium.MethodsInflorescences at different developmental stages were sampled from Brosimum gaudichaudii, Castilla elastica, Clarisia ilicifolia, Ficus pertusa, Maclura tinctoria and Morus nigra and processed for surface and anatomical analyses.Key ResultsThe inflorescence morphogenesis of the studied species is highly variable. The shape of the inflorescence meristem (bulging, hemispheric or elongated), the initiation order and arrangement of flowers along the receptacle and the occurrence of bracts vary between related species. This diversity originates early during inflorescence development. Brosimum gaudichaudii, C. elastica and F. pertusa have flowers enclosed or immersed within the receptacle, although inflorescences begin their development as flat and open structures, as occurs in the other three study species.ConclusionComparison of the inflorescence morphogenesis in Moraceae species allows us to infer that evolutionary ontogenetic changes driven by pollinators culminate in the enclosure of flowers inside the receptacle, as occurs in the Ficus syconium.     

Variation in scent emission among floral parts and inflorescence developmental stages in beetle-pollinated Protea species (Proteaceae)

Floral fragrances are an important component for pollinator attraction in beetle-pollinated flowers. Several genera in the Proteaceae contain beetle-pollinated species. However, there is no information on the floral scent chemistry of beetle-pollinated members of the family. In this paper we report on the spatial variation and differences between developmental stages in emission of inflorescence (flowerhead) volatiles of four South African Protea species (P. caffra, P. dracomontana, P. simplex, and P. welwitschii) that are pollinated by cetoniine beetles. The scents from different inflorescence parts (bracts, perianth, styles, and nectar) and from successive anthesis stages of whole inflorescences were sampled using dynamic headspace collection and identified using GC–MS. Although the four species shared many scent compounds, possibly reflecting their close phylogenetic relationships and common pollinators, they showed significant differences in overall scent composition due to various species-specific compounds, such as the unique tiglate esters found in the scent of P. welwitschii. The strongest emissions and largest number of volatiles, especially monoterpenes, were from inflorescences at full pollen dehiscence. Senescing inflorescences of two species and nectars of all species emitted proportionally high amounts of acetoin (3-hydroxy-2-butanone) and aromatic alcohols, typical fermentation products. As a consequence, the scent composition of nectar was much more similar among species than was the scent composition of other parts of the inflorescence. These results illustrate how the blends of compounds that make up the overall floral scent are a dynamic consequence of emissions from various plant parts.     

Comparative leaf anatomy and morphology of some neotropical Rutaceae: Pilocarpus Vahl and related genera

Previous anatomical studies have been restricted to the foliar aspects of Pilocarpus. However, no anatomical studies analyzing the foliar aspects of Pilocarpus in relation to related genera have been carried out. Therefore, the aim of this study was to identify characters for future taxonomic and phylogenetic studies in Rutaceae, particularly in Pilocarpus, and to discuss the characteristics associated with the simple or compound leaf condition for the group. The petiole and the leaf blade of 14 neotropical Rutaceae species were analyzed, and the following characteristics were observed in all leaves studied: stomata on both surfaces; secretory cavities, including mesophyll type; camptodromous?Cbrochidodromous venation pattern; and free vascular cylinder in the basal region of the petiole. Additional promising characters were identified for future taxonomic and phylogenetic studies in the Rutaceae family, especially for the Pilocarpus genera.     

SPIRAL DEVELOPMENTAL PATTERNS IN THE STEM AND INFLORESCENCE OF LILIUM TIGRINUM

Extensive correlations in spirality were observed among vegetative and floral organs in Lilium tigrinum Ker. Organs involved were vegetative leaves, bracts, and bracteoles. These correlations varied in their degree of constancy depending upon the organs involved. The mature inflorescences of L. tigrinum appeared to fit the common definition of a raceme. In 67.3% of the flowers at node 3 on the raceme, the bract-bracteole spirals reversed the spiral of vegetative leaves on the stem. These reversals resembled those observed on essentially cymose inflorescences of certain members of the Caryophyllaceae. Cymose branching was found to be an invariable feature of the inflorescence of L. tigrinum when secondary flowers appear. The apparently indeterminate tips of inflorescence main axes were interpreted as exhibiting stages in progression from a basically determinate (cymose) inflorescence. It was concluded that the ancestors of L. tigrinum had well-developed cymose branching patterns in the inflorescence. Reversal of stem spirals by the bract-bracteole spirals at the apices of many inflorescences was considered to be the result of complete utilization of the inflorescence meristem. Explanations for those reversals were provided by the field theory and by the theory of the first available space.     

Phylogeny of the Southeast Asian endemic genus Neocinnamomum H. Liu (Lauraceae)

A phylogenetic analysis of Neocinnamomum H. Liu and related genera was conducted using psbA–trnH, trnK cpDNA regions, and the ITS nrDNA segment. Neocinnamomum was confirmed to be monophyletic, and an evolutionary series of inflorescence development within the genus was recognized. The compound thyrse seen in N. caudatum is reduced to the few- to many-flowered condensed inflorescences with a poorly defined branching system seen in most species and ultimately to the 1-flowered inflorescence seen in N. atjehense. Consensus network analysis (CNA) suggested that long-branch attraction is responsible for the observed close relationship between Neocinnamomum and Cassytha L. in a combined analysis of the complete data. In contrast, the sister relationship of Neocinnamomum and Caryodaphnopsis seen in the Bayesian analyses of the partial combined matrix was supported by CNA and is also supported by morphology and wood and bark anatomy. The close similarity of the compound thyrse of less derived Neocinnamomum species to the thyrsoid inflorescences of some Caryodaphnopsis species is also seen as strong support for their affinity.