The Search for Geometrical Parameters That Represent the Dynamic Nature of Phyllotaxis in Plants

The shoot apical meristem (SAM) is the main growth centre that produces lateral organs such as leaves in specific and precise symmetrical patterns. The main goal of this commentary is to explore the link between phyllotactic parameters such as the plastochrone ratio (R) as well as Γ (relationship between the size of the SAM and the size of primordia) and growth processes involved in the expression of symmetrical patterns at the level of the SAM. It is also possible to deduce the values of these parameters from measures of the apical area and the radius of the SAM. A comparative analysis of phyllotactic parameters for three species (Begonia scabrida, Euterpe oleracea, and Anagallis arvensis) for which ‘dynamic’ data are available reveals that empirical and theoretical values of R and Γ can differ, indicating that characters defining these parameters are subject to developmental constraints that in turn determine the boundary conditions for the dynamic manifestation of phyllotactic patterns. One of the main challenges that remains is the ability to consistently and effectively observe the dynamic changes taking place at the SAM (in real time) over an extended period

The Search for Geometrical Parameters That Represent the Dynamic Nature of Phyllotaxis in Plants

The shoot apical meristem (SAM) is the main growth centre that produces lateral organs such as leaves in specific and precise symmetrical patterns. The main goal of this commentary is to explore the link between phyllotactic parameters such as the plastochrone ratio (R) as well as Γ (relationship between the size of the SAM and the size of primordia) and growth processes involved in the expression of symmetrical patterns at the level of the SAM. It is also possible to deduce the values of these parameters from measures of the apical area and the radius of the SAM. A comparative analysis of phyllotactic parameters for three species (Begonia scabrida, Euterpe oleracea, and Anagallis arvensis) for which ‘dynamic’ data are available reveals that empirical and theoretical values of R and Γ can differ, indicating that characters defining these parameters are subject to developmental constraints that in turn determine the boundary conditions for the dynamic manifestation of phyllotactic patterns. One of the main challenges that remains is the ability to consistently and effectively observe the dynamic changes taking place at the SAM (in real time) over an extended period

Thermogenic patterns in Philodendron ornatum and P. grandifolium: a comparative analysis

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Architecture de l'appareil végétatif et organisation florale du <i>Dracontium polyphyllum</i> L. (Araceae)

Une description de l\u27appareil végétatif, du développement de la feuille et de l\u27anatomie florale du Dracontium polyphyllum est présentée dans le cadre d\u27une analyse comparative avec les genres Anchomanes et Amorphophallus. Du point de vue architectural, le D. polyphyllum peut être classé dans trois catégories différentes selon le cadre théorique adopté. Si l\u27on adopte la classification d\u27Engler (1877), cette espèce fait partie du type V de la septième série qui comprend plusieurs espèces à tubercules. D\u27autre part, si l\u27on adopte la classification architecturale d\u27Hallé &amp; Oldeman (1970), le D. polyphyllum correspond au modèle de Chamberlain. Finalement, si l\u27on suit la classification de Ray (1987), cette espèce aurait une organisation de type anisophylle proleptique. La lobation foliaire a un mode de développement marginal et intramarginal. Dans l\u27inflorescence, la maturation des fleurs est basipète. La fleur comprend trois ou quatre carpelles et généralement de 9 à 12 étamines.A description of the vegetative architecture, the development of the leaf and the floral anatomy of Dracontium polyphyllum is presented in comparison with the genera Anchomanes and Amorphophallus. From an architectural point of view, D. polyphyllum can be put in three different categories depending on the theoretical framework chosen. If we use the classification of Engler (1877), this species belongs to the type V of the seventh series, which comprises many tuberous species. On the other hand, if we adopt the architectural classification of Hallé &amp; Oldeman (1970), D. polyphyllum corresponds to Chamberlains model. Finally, if we follow Rays classification (1987) this species would have an organisation of the proleptic anisophyllous type. The foliar lobation has a marginal and intramarginal mode of development. The flower maturation in the inflorescence is basipetal. The flower comprises three or four carpels and generally 9 to 12 stamens.</p

Quantitative Developmental Analysis of Homeotic Changes in the Inflorescence of Philodendron (Araceae)

Background and Aims The inflorescence of Philodendron constitutes an interesting morphological model to analyse the phenomenon of homeosis quantitatively at the floral level. The specific goals of this study were (1) to characterize and quantify the range of homeotic transformation in Philodendron billietiae, and (2) to test the hypothesis that the nature of flowers surrounding atypical bisexual flowers (ABFs) channel the morphological potentialities of atypical bisexual flowers. Methods Inflorescences of P. billietiae at different stages of development were observed using SEM. The number of appendices in male, female and sterile flowers were counted on 11 young inflorescences (5–6 flowers per inflorescence). The number of staminodes and carpels on ABFs were counted on 19 inflorescences (n = 143). These data were used for regression and ANOVA analyses. Results There was an average of 4·1 stamens per male flower, 9·8 carpels per female flower and 6·8 staminodes per sterile male flower. There was an average of 7·3 floral appendices per atypical flower. Staminodes and carpels are inserted on the same whorl in ABFs. A negative exponential relationship was found between the average number of staminodes and the number of carpels in ABFs. If only the ABFs consisting of less than six carpels are considered, there is a linear relationship between the number of carpels and the average number of staminodes. The value of the slope of the regression equation indicates that on average, in P. billietiae, 1·36 carpels are replaced by one staminode. Conclusions In P. billietiae, the number of appendages in female flowers imposes a constraint on the maximum total number of appendages (carpels and staminodes) that can develop on ABFs. The quantitative analyses indicate that the average number of different types of floral appendages on an ABF and the number of organs involved in a homeotic transformation are two independent phenomena

Floral development of Urosphatha : merosity and phylogeny in the Lasioideae (Araceae)

In this paper we study merosity in the genus Urospatha within the framework of a resolved phylogeny of the Araceae. We analyse how a transition from dimerous or tetramerous merosity to pentamerous or hexamerous merosity can occur developmentally in the Lasioideae. In Urospatha, initiation of floral primordia along the inflorescence is acropetal, while development of flowers is basipetal. This indicates the presence of two distinct phases in the development of the Urospatha inflorescence. The first phase corresponds to initiation of flowers and establishment of the phyllotactic pattern, and the second phase to differentiation of floral organs. Urospatha is characterized by the presence of trimerous, tetramerous, pentamerous and rarely hexamerous flowers. In all types of flowers, the stamens are closely associated and opposite to the tepals. Pentamerous flowers are formed by addition of a sector comprising a stamen and tepal. Likewise, in the case of hexamerous flowers, two sectors are added. In the Lasioideae, the increase in the number of tepals and stamens is linked with two developmental processes that have appeared independently in the subfamily: (1) addition of one or two stamen-petal sectors (Anaphyllopsis and Urospatha), and (2) independent increase in the number of tepals and stamens on whorls, more or less organized and inserted in alternate position (Dracontium). Tetramerous whorls as they occur in basal Lasioideae would be homologous to two dimerous whorls from an evolutionary point of view

Floral development of Dieffenbachia and the occurrence of atypical flowers in Araceae

Background The floral development of Dieffenbachia seguine (N. J. Jacquin) Schott is analysed in relation to the molecular phylogeny of the Spathicarpae by Cusimano et al. (Am J Bot 98:654–668, 2011). Results The initiation of discoid floral primordia occurs acropetally on the surface of the spadix. Female flowers, atypical bisexual flowers, sterile male flowers, and male flowers share the same phyllotactic spirals on the spadix. Four or five stamen primordia are initiated simultaneously on the periphery of the male floral meristem. During early stages of stamen initiation, individual stamen primordia are connate at their base. In a synandrium, stamen fusion occurs very early during their developmental cycle with the stamens being already united laterally when longitudinal elongation occurs. The staminodes are also initiated on the periphery of the discoid floral primordium, and their number varies from four to six. The development of the fused staminodes will eventually form a longitudinal cavity in the center of the mature synandrode. The atypical flowers located in the intermediate zone range in morphology from aborted female flowers to rudimentary sterile male flowers with incomplete staminodes. Conclusions The development of the female flower of Dieffenbachia Schott presents some similarities with atypical bisexual flowers of Cercestis Schott representing one of three types of aberrant flower forms in the family. From a developmental point of view and in the context of a phylogeny of the group, we believe that the presence of staminodes in the female zone constitutes a plesiomorphy in the tribe Spathicarpeae