Quantitative floral development in Pseudolysimachion (Scrophulariaceae): intraspecific variation and comparison with Veronica and Veronicastrum

Intraspecific variation in floral development was studied in four morphologically distinct strains of Pseudolysimachion longifolium and two of P. spicatum. Size increase of whole buds from living plants of P. longifolium was followed in absolute time. Growth rates were homogeneous within inflorescences and within individual plants, and significantly different between individual plants. Organ growth trajectories (plotted as organ size over gynoecium size) differed little among individuals of Pseudolysimachion belonging to morphologically distinct strains; variation was most pronounced in the calyx. Corolla tube as well as calyx and corolla lobe measurements varied more during the early stages of development than near maturity, suggesting constraints on mature flower form. In addition to intraspecific variation, floral development in Pseudolysimachion was compared with that in related Veronica chamaedrys and Veronicastrum virginicum, using data from a previous study. Mature flowers of Pseudolysimachion have long corolla tubes similar to those of Veronicastrum and long corolla lobes similar to those of Veronica. The trajectories of most organs of Pseudolysimachion were intermediate between those of Veronica and Veronicastrum in position as well as in type of curve, i.e., different trajectories lead to similar end products; thus, the shapes of the mature organs are not strictly homologous and not indicative of close relationship.     

Floral morphogenesis in choripetalous and sympetalous members of Ericaceae s.l. (Ericales)

Choripetaly of Rhododendron tomentosum is the result of secondary reduction. Our data support earlier observations of P. Leins [4] that a rudimentary corolla tube occurs during early stages of floral development. Choripetaly of Empetrum may be a plesiomorphic condition, because no vestiges of corolla tube were detected throughout all stages of flower development. However, a complete loss of corolla tube cannot be excluded. The type of congenital petal fusion varies within a group of closely related taxa of Ericaceae: Phyllodoce caerulea has late sympetaly while Loiseleuria procumbens has early sympetaly. In contrast, in euasterids, the type of sympetaly appears to characterize taxa of higher rank.     

Floral Development at Multiple Spatial Scales in Polygonum jucundum (Polygonaceae), a Distylous Species with Broadly Open Flowers

Distyly, a special polymorph, has evolved in many groups of angiosperms and has attracted attention since Darwin’s time. Development studies on distylous taxa have helped us to understand the evolutionary process of this polymorph, but most of these studies focus on species with narrowly tubular corolla. Here, we studied the floral development of Polygonum jucundum, a distylous species with broadly open flowers, at multiple spatial scales. Results showed that the difference in stigma height between flowers of the two morphs was caused by differences in style growth throughout the entire floral development process. The observed difference in anther heights between the two morphs was because the filaments grew faster in short-styled (SS) than in long-styled (LS) flowers in the later stages of floral development. In addition, the longer styles in LS flowers than in SS flowers was because of faster cell division in the early stages of floral development. However, SS flowers had longer filaments than LS flowers primarily because of greater cell elongation. These results indicate that floral development in P. jucundum differs from that of distylous taxa with floral tubes shown in previous studies. Further, we conclude that the presence of distyly in species with open flowers is a result of convergent evolution.     

Pollen morphology in the genus Veronica L. (Plantaginaceae) and its systematic significance

Pollen grains of 30, mainly annual, species from 134 populations of the genus Veronica (Plantaginaceae, formerly Scrophulariaceae) from the Mediterranean Region, have been studied with light and scanning electron microscopy. Three pollen types are defined based on pollen size and exine surface sculpture. In some cases within the study group pollen size can be useful in species determination. Hypothetical relationships of pollen grain size and aperture number with ploidy level, style length and corolla diameter are discussed. The ornamentation of the exine in Veronica, although generally a conservative character within the genus, gives some additional support to the most recent infrageneric classification of Veronica.     

Early floral development of Pentaphylacaceae (Ericales) and its systematic implications

Early floral development of four species from the genera Anneslea, Cleyera, Eurya, and Ternstroemia of Pentaphylacaceae, was studied comparatively using scanning electron microscopy. Together with earlier studies in Euryodendron and Adinandra, 6 out of 12 genera of Pentaphylacaceae have now been studied for their floral development. The usually pentamerous flowers of these taxa share a number of developmental features: the perianth organs appear in a clockwise or anticlockwise spiral sequence on the floral apex with relatively long plastochrons between successive organs, resulting in conspicuous size differences among perianth organs during early developmental stages. The early development of the usually polystemonous androecium is characterized by an indistinct ring-primordium and a mostly concave floral apex; individual stamens appear subsequently on this ring-primordium. However, further development of the androecium differs conspicuously among taxa and we describe three main developmental patterns for the family including features such as centripetal stamen whorls and stamens fascicles. Unusual features of floral development and organization of Pentaphylacaceae include: (1) a pronounced spiral sequence of organ appearance during early floral development in perianth and androecium; (2) the occurrence of paired organs in the corolla and the androecium of some species; (3) sepals and petals that are positioned opposite from each other in the genera Anneslea and Ternstroemia; and (4) a concave floral apex at the beginning of androecium development. From a systematic point of view our results clearly support a close relationship between Anneslea and Ternstroemia and also suggest a closer relationship among Adinandra, Cleyera, and Euryodendron on the one hand and between Eurya and Visnea on the other. Further, our developmental study stresses the differences between Pentaphylacaceae and Theaceae, which earlier where thought to form a natural group of plants. While high stamen numbers are achieved via centripetal pattern of stamen formation in the former family, stamens are formed centrifugally in the latter.     

Evolution of flower shape inVeroniceae (Scrophulariaceae)

Floral evolution in the tribeVeroniceae was examined using phylogenetic analysis combining 24 adult morphology and chromosome number characters with 22 qualitative and quantitative floral development characters. Taxa sampled included nine species ofVeroniceae and as an outgroup one species each ofDigitaleae andVerbasceae. Veronica, Besseya, andSynthyris formed one clade, subtended byPseudolysimachion and then by theHebe group;Veronicastrum orWulfenia represent the basal-most branch of the tribe. The ancestral flowers of theVeroniceae may have been small with moderately short corolla tubes and lobes; long corolla tubes arose four times in the tribe and large corolla lobes twice.     

Mating system variation in Veronica (Plantaginaceae): inferences from pollen/ovule ratios and other reproductive traits

The pollen–ovule ratio (P/O) is commonly used to estimate the mode of sexual reproduction in flowering plants. In previous studies, a clear correspondence has been detected between this character and the degree of autogamy. We here investigate variation in this character and its expected correlates in the genus Veronica (Plantaginaceae). Pollen–ovule ratios of 45 species representing eleven percent of all the species in the genus were investigated and compared with results from crossing experiments from previous studies. In addition, multiple populations of 17 of the 45 studied species were sampled and a controlled‐environment experiment was conducted to evaluate the extent of intraspecific variation. Moreover, relationships between P/O and other primary and secondary reproductive characters of the Veronica flower were investigated in relation to a phylogenetic hypothesis in order to determine the phylogenetic constraints on reproductive characters. The differences in P/O among species correspond well to the diversity of mating systems in Veronica and correlate well with other floral characters such as corolla size. These characters together seem to allow a powerful and fast tool to infer mating systems. However, causes for intraspecific variation of P/O, such as different cytotypes, ecotypes or different growth conditions, need to be considered.     

Patterns of contemporary phenotypic selection and flower integration in the hummingbird‐pollinated Nicotiana glauca between populations with different flower–pollinator combinations

We studied six populations of the hummingbird‐pollinated Nicotiana glauca to determine if the marked differences in the degree of floral‐pollinator mismatch between populations promote divergences in the pattern of pollinator‐mediated phenotypic selection on single traits and on the evolution of complexes of many interacting floral traits. We found evidence that flower phenotype is being shaped by pollinator‐mediated phenotypic selection, since corolla length was consistently under contemporary directional or stabilizing selection. Weak directional selection for longer corollas was found in two populations with low flower–pollinator mismatch; much stronger directional selection was detected for shorter corollas in two populations with high flower–pollinator mismatch; finally, the remaining two populations with intermediate flower–pollinator mismatch showed stabilizing selection for corolla length. N. glauca populations differed in every flower character measured but variations in pollinator‐mediated selection among populations were only observed for corolla length. Multiple covariation among traits was favoured, as suggested by the predominately functional patterns of integration and selection of complexes of many interacting floral traits. This was consistent with the patterns of correlational selection exhibited by four of the six populations, where corolla length was under significant selection in combination with corolla width, style length or stamen length. Overall floral integration was relatively high in all populations but phenotypic integration patterns were not clearly accounted by the degree of flower–pollinator mismatch or type of phenotypic selection, suggesting that trait covariation at the entire flower level is not explained by the current scenario of pollinator‐mediated selection.     

FLORAL DEVELOPMENT IN CAESALPINIA (LEGUMINOSAE)

Utilizing scanning electron microscopy, we studied the early floral ontogeny of three species of Caesalpinia (Leguminosae: Caesalpinioideae): C. cassioides, C. pulcherrima, and C. vesicaria. Interspecific differences among the three are minor at early and middle stages of floral development. Members of the calyx, corolla, first stamen whorl, and second stamen whorl appear in acropetal order, except that the carpel is present before appearance of the last three inner stamens. Sepals are formed in generally unidirectional succession, beginning with one on the abaxial side next to the subtending bracts, followed by the two lateral sepals and adaxial sepal, then lastly the other adaxial sepal. In one flower of C. vesicaria, sepals were helically initiated. In the calyx, the first-initiated sepal maintains a size advantage over the other four sepals and eventually becomes cucullate, enveloping the remaining parts of the flower. The cucullate abaxial sepal is found in the majority of species of the genus Caesalpinia. Petals, outer stamens, and inner stamens are formed unidirectionally in each whorl from the abaxial to the adaxial sides of the flower. Abaxial stamens are present before the last petals are visible as mounds on the adaxial side, so that the floral apex is engaged in initiation of different categories of floral organs at the same time.     

A COMPARISON OF CLEISTOGAMOUS AND CHASMOGAMOUS FLORAL DEVELOPMENT IN COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)

An individual of Collomia grandiflora typically produces both closed or cleistogamous (CL) and open or chasmogamous (CH) flowers. The developmental origin of these dimorphic floral types within a plant was investigated using histological techniques, allometric relationships, and scanning electron microscopy. Prior to archesporal cell stage in the anthers, CL and CH meristems are indistinguishable. In the CL anther, an absence of ventral locule cell differentiation together with a shorter period of time between archesporial cell differentiation and meiosis in the two dorsal locules results in accelerated anther dehiscence and a smaller mature anther size and pollen grain number. Divergence between the CL and CH patterns of corolla development is coincident with microspore mitosis in the CH anther. At this point, there is an increase in growth in corolla length relative to growth in calyx length in the CH flower which does not occur in the CL flower. Calyx and ovary development are similar in the two floral forms; however, ovary expansion due to fertilization occurs earlier in the CL flower as a result of precocious anther development and stigma receptivity. The hypothesis that anther differentiation may trigger organ growth rate changes and differentiation events in the flower and hypothetical roles for abscisic acid and gibberellin in modifying floral development in C. grandiflora are discussed.     

Pollinator shifts,contingent evolution,and evolutionary constraint drive floral disparity in Salvia (Lamiaceae): Evidence from morphometrics and phylogenetic comparative methods

Switches in pollinators have been argued to be key drivers of floral evolution in angiosperms. However, few studies have tested the relationship between floral shape evolution and switches in pollination in large clades. In concert with a dated phylogeny, we present a morphometric analysis of corolla, anther connective, and style shape across 44% of nearly 1000 species of Salvia (Lamiaceae) and test four hypotheses of floral evolution. We demonstrate that floral morphospace of New World (NW) Salvia is largely distinct from that of Old World (OW) Salvia and that these differences are pollinator driven; shifts in floral morphology sometimes mirror shifts in pollinators; anther connectives (key constituents of the Salvia staminal lever) and styles co-evolved from curved to linear shapes following shifts from bee to bird pollination; and morphological differences between NW and OW bee flowers are partly the legacy of constraints imposed by an earlier shift to bird pollination in the NW. The distinctive staminal lever in Salvia is a morphologically diverse structure that has evolved in concert with both the corolla and style, under different pollinator pressures, and in contingent fashion.     

Floral ontogeny inMazus pumilus (Scrophulariaceae)

InMazus pumilus, all the floral appendages are initiated in acropetal sequence in the second cell layer (except stamens) of the floral primordium by periclinal divisions. The actinomorphic calyx tube is formed due to zonal growth. The zygomorphy in corolla is evident from the inception of petal primordia which arise sequentially as independent units in order of one anterior, a pair of anterio-lateral followed by a pair of posterio-lateral. Later these primordia exhibit differential growth because of which zygomorphy becomes more pronounced. The upper corolla tube is formed by interprimordial growth and lower corolla tube by zonal growth. Stamens are initiated in the third layer of the floral apex. Unlike sepals and petals, in the development of stamens (4) underlying cells of corpus also contribute. Posterior stamen is absent. The stamens become epipetalous because of interprimordial and zonal growth in the common region below the bases of petals as well as stamens. The two carpel primordia arise as crescent shaped structures which become continuous due to interprimordial growth. The ovary is formed by a ring of zonal meristem. The style develops later between stigma and ovary because of intercalary growth. The residual apex grows vertically along with the ovary and forms the septum of the ovary. All the floral appendages exhibit similar pattern of histogenesis and early growth suggesting thereby the appendicular nature of these appendages.     

弯齿盾果草(紫草科)花序及花的形态发生

以弯齿盾果草不同发育时期的花芽为材料,在体视显微镜解剖观察的基础上使用扫描电镜对弯齿盾果草花序、花及果实的发育过程进行了观察。结果显示:(1)弯齿盾果草的花序是由最初的一个球形花序原基经过多次分裂形成的,且花序发生式样符合蝎尾状聚伞花序结构,而非通常所描述的镰状或螺状聚伞花序;花序发生过程中无单一主轴,花序轴是由侧枝连接而成,每一朵花原基有其对应的1枚苞片,下一花原基是从相邻的上一枚苞腋里发生,相邻两花原基交错互生。(2)花器官的发生是按照花萼原基、花冠原基、雄蕊原基和雌蕊原基的顺序发育,但雄蕊原基的花药部分发育速度要比花冠原基快,所以花器官的发育是按照花萼、雄蕊、花冠和雌蕊的顺序发育。(3)子房四深裂结构是由4个原基分别发育,而后相互靠拢而成。(4)小坚果表面的附属结构发生于子房发育后期,其背面的内外层突起分别是由生长较快的外部组织的边缘通过上部内缩和下部向外环状生长形成。     

STRUCTURE AND DEVELOPMENT OF THE PERIANTH IN DOWNINGIA BACIGALUPII

The structure and ontogeny of the calyx and corolla of Downingia bacigalupii Weiler (Campanulaceae; Lobelioideae) were investigated for the purpose of comparing perianth development with previous observations on the floral bract, as well as elucidating the mechanism of development of the zygomorphic, sympetalous corolla. Sepals are uni-traced with a palmate, reticulate venation. They have basal and apical hydathodes, as well as storage tracheids. Sepals show a reduction in size, venation and hydathode number when compared to the bract. The pentamerous, zygomorphic corolla is bilabiate, consisting of a three-lobed adaxial lip and a two-lobed abaxial lip connected by a short tubular region. The constituent petal lobes are also uni-traced and have a reticulate venation, resembling that of the sepal and bract, but lack storage tracheids and hydathodes. Sepals arise in an adaxial to abaxial succession and are initiated in the outer corpus layer of the floral apex. Expansion of the floral apex follows and is accompanied by the establishment of a second tunica layer. Sepals undergo apical, marginal, and intercalary growth accompanied by acropetal differentiation of procambium. The petals arise simultaneously and are initiated in the second tunica layer and the outer corpus cells. After initiation, the petals exhibit a period of apical and marginal growth followed by intercalary growth. Apical growth in petals is less protracted than in sepals, but plate meristem activity is more extensive. The free petal lobes become temporarily fused by an interlocking of marginal epidermal layers, but they separate at anthesis. Zonal growth beneath the originally free lobes forms the tube and lip regions of the sympetalous corolla. Zygomorphy is evident from the time of initiation of petals and is accentuated by later differential growth. Comparative observations of corolla ontogeny in autogamous species of Doumingia indicate that the reduced corollas in these taxa are derived by a simple process of neoteny.     

Floral evolution in Lithospermum (Boraginaceae): independent origins of similar flower types

In Lithospermum (Boraginaceae), floral diversity is quite large, with variation in individual quantitative and qualitative traits as well as suites of floral characteristics. The present study utilizes phylogenetic, morphometric and developmental methodologies to investigate patterns of floral evolution, of individual and suites of traits, in the genus and among related genera. The evolutionary patterns of eight quantitative and five qualitative traits were reconstructed, and morphometrics and the evolution of floral morphospace were examined in the genus. Floral developmental patterns were established with light and scanning electron microscopy. Phylogenetic analyses provided evidence that derived flower types have each evolved multiple times, with differences in the manner in which these flower types arose. Floral morphospace has increased throughout the evolution of Lithospermum. Floral developmental patterns and cell lengths of floral organs at anthesis provided evidence that, in Lithospermum, an increase in the length of the sexual organs of flowers involves both longer cells and a greater number of mitotic divisions, but an increase in the length of the corolla is primarily a result of a larger number of cell divisions. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 213–228.     

FLORAL DEVELOPMENT OF COCHLOSPERMUM TINCTORIUM AND BIXA ORELLANA WITH SPECIAL EMPHASIS ON THE ANDROECIUM

The initiation and development of the flower of Bixa orellana L. and Cochlospermum tinctorium A. Rich, were investigated using the scanning electron microscope to elucidate the nature of the androecial development and the relationships of both taxa. Initiation of floral buds starts with the inception of five sepals in a 2/5 sequence between two bracteoles. The petals are formed successively on the irregular pentagonal apex in a phyllotactic pattern different from that of the calyx. Stamen development proceeds centrifugally on a broad circular primordium or ringwall, which attains its final size at the time of initiation of individual stamens. Stamen primordia arise in successive whorls without connection to the perianth. The residue of the apex is differentiated into a gynoecial circular primordium. In Cochlospermum 3 to 4 carpels are initiated; in Bixa no individual carpels are visible. The origin of the androecial circular primordium is discussed in relation to other types of androecial development. A comparison is made with existing theories of the evolution of multistaminate androecia. Few differences were found in the floral development of Bixa and Cochlospermum, except in the gynoecium. It is proposed to retain them in a single family Bixaceae for a number of reasons. The floral development supports a thealean, dillenialean, or violalean affinity rather than a malvalean. The inception of a broad androecial circular primordium is highly different from the development in Malvales, where more space for stamens is provided by the continuous growth of a tube.     

Island–mainland difference in <Emphasis Type="Italic">Nicotiana glauca</Emphasis> (Solanaceae) corolla length: a product of pollinator-mediated selection?

A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist. I first determined differences in floral morphology and pollinator composition between island and mainland populations of N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites. I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift.     

EMASCULATION EFFECTS ON FILAMENT GROWTH IN IPOMOEA NIL (CONVOLVULACEAE)

Filament growth in the morning glory Ipomoea nil is promoted by gibberellic acid (GA₃) and inhibited by ethylene production during the earlier stages in development (Koning and Raab, 1987). The effects of anther removal on filament growth were examined in I. nil. Three-quarters of the calyx and corolla tissues were removed in order to emasculate the stamens. This removal caused filament growth to be inhibited in the intact stamens (69 hr before anthesis) as well as the emasculated stamens (69 to 21 hr before anthesis). When the ethylene biosynthesis inhibitors CoCl₂ and aminoethoxyvinylglycine (AVG) were applied in separate experiments (to eliminate wound ethylene generated by the damaged tissues), filament growth was promoted to control levels observed in intact flower buds (69 hr before anthesis). Our data suggest that the wounding effect from the calyx and corolla tissues and subsequent reduction in filament growth override any observable effects with anther removal on filament growth. Apparently, the removal of the calyx and corolla tissues severs a normal hormonal relationship between these floral organs and the developing filament.     

花冠对紫茉莉繁殖适合度的影响

以授粉后具花闭合特性的紫茉莉为研究材料,通过在不同天气状况下作去花冠和存留花冠处理,观察花冠对花粉活力、柱头可授性及结实率等繁殖特性的影响。结果表明:紫茉莉自然存留花冠比去花冠的花粉活力、柱头可授性、柱头上的花粉数及柱头上花粉萌发率各指标达最高值的时间重叠性更强,并以阴天存留花冠的最强。存留花冠通过这种时间的重叠性来保证花粉在柱头上的萌发,产生了有利的繁殖适合度。越晚去花冠结实率越高,结实率呈现花闭合自然存留花冠>花冠闭合期去花冠>散粉初期去花冠>花冠展开期去花冠的规律。因此,花冠对紫茉莉繁殖适合度具有利影响。紫茉莉花冠的存留提高了繁殖适合度,增强了对环境的适应能力。     

A corolla-and carpel-abundant,non-specific lipid transfer protein gene is expressed in the epidermis and parenchyma of Gerbera hybrida var. Regina (Compositae)

We are examining the floral organ differentiation in Compositae by isolating and characterizing corolla abundant genes. Differential screening of a cDNa library made from the ray floret corolla of Gerbera hybrida var. Regina revealed an abundant cDNA clone which is expressed in the corolla but not in leaves. This cDNA (gltp1) codes for a polypeptide similar to non-specific lipid transfer proteins of the plants. The gltp1 gene is expressed only in the corolla and carpels and is developmentally regulated during corolla development. The gltp1 mRNA accumulates both in epidermal cell layers and in the mesophyll of the corolla. In the stylar part of the carpel, the gltp1 mRNA can be detected in the epidermal and in parenchymal cells but not in the transmitting tissue. Analogous patterns of gltp1 expression in the corolla and carpel may indicate that similar genetic programmes operate during the development of these two tissues.