Floral Morphology Research Articles

A concise study on the floral biology of Thevetia peruviana morphovariants

Thevetia peruviana, an ornamental medicinal plant of the family Apocynaceae blooms in different colour shades of yellow, orange and white, and is considered morphological replicas of its original parental type. A concise morpho-anatomical study has been carried out on the floral biology of these three morphovariants emphasizing biometrics of various floral parts, the architecture of corolla tube and corolline corona, adnation of anther stigmatic head complex and ovule to embryo formation, using the hand as well as microtome sections, to analyze the similarities and differences among these specimens. Appendiculate and smooth walled hairs in corolla tube, germination of pollen grains in a lateral stigmatic notch, appression of anther lobes on 10-lobed incompletely fused stigma, triaperturate pollen grains, ovule developmental stages, entry of pollen tube into ovule, attachment of funicle on placenta etc are some of the enchanting valuable scientific observations under light microscopy. Gross morphological variations noted in the overall size of various floral parts are regarded as negligible ones, which may happen due to environmental factors. Floral morphology alone is insufficient to give distinct varietal status in the hierarchy of classification, but corolla shades, of course, are of prime importance for phenotypic differentiation, and a multidisciplinary approach will help to expose untapped characters, useful for future studies below the rank at the subspecies level.

Secondary pollinators contribute to reproductive success of a pink-flowered sand verbena population.

Secondary pollinators contribute to reproductive success of a pink-flowered sand verbena population.

Chromosome-Level Assembly of Flowering Cherry (Prunus campanulata) Provides Insight into Anthocyanin Accumulation.

The flowering cherries (genus Prunus, subgenus Cerasus) are popular ornamental trees in China, Japan, Korea, and elsewhere. Prunus campanulata Maxim. is an important species of flowering cherry native to Southern China, which is also distributed in Taiwan, the Ryukyu Islands of Japan, and Vietnam. It produces bell-shaped flowers with colors ranging from bright pink to crimson during the Chinese Spring Festival from January to March each year. We selected the P. campanulata cultivar "Lianmeiren", with only 0.54% of heterozygosity, as the focus of this study, and generated a high-quality chromosome-scale genome assembly of P. campanulata by combining Pacific Biosciences (PacBio) single-molecule sequencing, 10× Genomics sequencing, and high-throughput chromosome conformation capture (Hi-C) technology. We first assembled a 300.48 Mb genome assembly with a contig N50 length of 2.02 Mb. In total, 28,319 protein-coding genes were predicted from the genome, 95.8% of which were functionally annotated. Phylogenetic analyses indicated that P. campanulata diverged from a common ancestor of cherry approximately 15.1 million years ago. Comparative genomic analyses showed that the expanded gene families were significantly involved in ribosome biogenesis, diterpenoid biosynthesis, flavonoid biosynthesis, and circadian rhythm. Furthermore, we identified 171 MYB genes from the P. campanulata genome. Based on the RNA-seq of five organs at three flowering stages, expression analyses revealed that the majority of the MYB genes exhibited tissue-specific expression patterns, and some genes were identified as being associated with anthocyanin accumulation. This reference sequence is an important resource for further studies of floral morphology and phenology, and comparative genomics of the subgenera Cerasus and Prunus.

MADS-Box Subfamily Gene GmAP3 from Glycine max Regulates Early Flowering and Flower Development.

AP3 has been studied and is reported to affect structural changes in floral organs in various plants. However, the function of the soybean AP3 genes in flower development is unknown. Here, the full-length cDNA sequence of GmAP3 was obtained by RACE and it was verified that it belongs to the MADS-box subfamily by a bioinformatics analysis. The expression of GmAP3 is closely related to the expression of essential enzyme genes related to flower development. Yeast two-hybrid assays demonstrated that GmAP3 interacts with AP1 to determine the identity of flower organ development. A follow-up analysis showed that overexpression of the GmAP3 gene advanced flowering time and resulted in changes in floral organ morphology. The average flowering time of overexpressed soybean and tobacco plants was 6-8 days earlier than that of wild-type plants, and the average flowering time of gene-edited soybean and tobacco plants was 6-11 days later than that of wild-type plants. In conclusion, GmAP3 may directly or indirectly affect the flower development of soybean. The results of this study lay the foundation for further research on the biological functions of MADS transcriptional factors in soybeans.

Pollination of exotic fruit crops depends more on extant pollinators and landscape structure than on local management of domestic bees

Agricultural globalization has driven the expansion of exotic crops into new agricultural areas. Pollinator-dependent exotic crops not only have to face the abiotic constraints of the new cultivation regions but also deal with local pollinator assemblages, which may or may not fulfill pollination requirements. Here, we studied how three entomophilous exotic crops (kiwifruit, northern highbush blueberry and rabbiteye blueberry) adapt to a common pollination environment in new cultivation areas in Spain. For this, we assessed the pollination limitation of those crops, the contribution of insect assemblages to the pollination service, and the effect of landscape structure and the management of domestic pollinators on these assemblages. The three exotic crops showed large and diverse pollinator assemblages but differed in the assemblage composition and in the identity of the main pollinator species. Honeybee clearly dominated kiwifruit assemblages, representing almost 70 % of visits to flowers. Bumblebees and honeybee fairly equally dominated floral visits in highbush blueberry, and bumblebees accounted for more than 90% of visits in rabbiteye blueberry. Floral morphology partially explained interspecific differences in pollinator assemblages and led to the distinct contributions of the different insects to the different crops. Kiwifruit (but not blueberry) crops experienced pollination limitation that led to, on average, a 7.2 % reduction in fruit weight. This pollination limitation decreased when honeybee abundance rose. In all three crops, the local pollinator assemblages mostly depended on the landscape structure around orchards but were only affected by the management of domestic pollinators in rabbiteye blueberry crops. Our results highlight the importance of understanding the interspecific differences in the pollination ecology of new exotic crops before designing general management recommendations, and also question the use of managed pollinators before making an assessment of the contribution of extant insects to the pollination service.

Swallowtail butterflies and hawkmoths contribute equally to the pollination of Habenaria dentata (Orchidaceae)

Mixed pollination system with both diurnal and nocturnal visitors contributing to pollen transfer and seed set have been documented in many angiosperm species. The flowers of Habenaria species are usually green or white, with a long nectar secreting spur, and are usually interpreted as specialized for pollination by nocturnal moths. With a few exceptions, nocturnal moths and diurnal butterflies are both reported as pollinators of Habenaria species. However, the relative contributions made by moths versus butterflies to the reproductive success in the same orchid species has rarely been studied. We investigated the floral morphology, pollinators, pollination efficiency, and breeding system of Habenaria dentata in southern China. We showed that two species of diurnal swallowtail butterflies (Papilio helenus and Papilio memnon) and a species of crepuscular hawkmoth (Eupanacra mydon) were this orchid's effective pollinators. The pollinaria were attached to the eyes of these three insect species. Pollinator exclusion experiments showed that pollinarium removal and pollinium deposition rates on stigmas by butterflies (47.51% and 38.64%, respectively) were not significantly different from those made by hawkmoths (50.70% and 34.47%, respectively), indicating that diurnal and crepuscular visits contributed equally to reproductive success. As natural rates of insect-mediated pollination of our population of H. dentata resulted in fruit set rates of 93.33%, rejected the prospect that this population was pollinator limited. Hand pollination experiments indicated that H. dentata was self-compatible but without autonomous self-pollination. The proportion of well-developed seeds with large embryos in self-pollinated fruits was significantly lower than in cross-pollinated fruits, suggesting natural selection favors xenogamy. Our results highlighted the importance of both butterflies and hawkmoths contributing to the reproductive success of a rare orchid with a mixed pollination system.

A Taxonomic Revision of the Neotropical Genus Martiodendron (Fabaceae: Dialioideae)

Martiodendron (Leguminosae/Fabaceae) is a Neotropical genus of trees and shrubs comprising five species. It is characterized by its yellow pentamerous corolla, four to five long poricidal anthers and large, attractive red samaras; it represents an intermediate stage of floral reduction among the 17 genera of the subfamily Dialioideae, which display diverse floral morphologies including different types of reduced flowers in the perianth and androecium. The last taxonomic revision of Martiodendron was published some 60 years ago and there is frequent misidentification of specimens in herbaria, databases, and floristic works with mistreatment of taxa and unclear geographic distributions. Thus, circumscriptions of the species and varieties of the genus require reassessment in light of the substantial new data that has become available during the last several decades. Here, we synthesized morphological, geographical, and ecological data on the genus to produce a modern integrative taxonomic treatment. Our taxonomic concepts are underpinned by analysis of 352 herbarium specimens and substantial fieldwork in South America. We recognize five species and four varieties of Martiodendron. All of these taxa display high levels of morphological and geographical cohesion. One of the varieties, M. mediterraneum var. concinnum, is described as new to science. Detailed descriptions of each recognized taxa are accompanied by illustrations, distribution maps, conservation status assessments, and complete nomenclatural treatments with four new lectotypifications. An identification key and a morphometric analysis of fruits are also provided.

Genome Size, Flowering, and Breeding Compatibility in Osmanthus Accessions

Extending the range of Osmanthus species into more cold-hardy climates would open new opportunities for adoption and use of these species by growers, landscapers, and the public. Breeding improvement is hindered by few available cultivars and a lack of female or perfect flowers. The objectives of this study were to evaluate floral morphology and pollination biology of Osmanthus species available in the U.S. market. Thirty-three genotypes representing four species were evaluated in McMinnville, TN, USA for genome size, floral morphology, pollen viability, and self- and cross-compatibility. All genotypes were diploid with 2C genome sizes ranging from 2.89 to 3.21 pg. Perfect flowers were observed in all O. armatus and 82% of O. heterophyllus genotypes. All observed O. fortunei and O. fragrans genotypes had male-only flowers. Pollen viability based on staining and in vitro germination ranged from 8% to 98% and 6% to 53%, respectively. Pollen germination was observed on stigmas of 94.2% of O. armatus and O. heterophyllus flowers collected 24 hours after cross- or self-pollination. There was a significant association between cross type and percentage of flowers with pollen tubes reaching the ovaries; after 72 h, pollen tubes had reached the ovaries of in 67% of intraspecific crosses, 78% of interspecific crosses, and 0% of self crosses (χ2 = 26.5, p < 0.001). This study provides evidence of a self-incompatibility system in O. armatus and O. heterophyllus and provides insights into opportunities and challenges for Osmanthus hybrid breeding.

Transcriptome and morphological analyses of double flower formation in Dianthus chinensis

The double flower developmental process is regulated via a complex transcriptional regulatory network. To understand this highly dynamic and complex developmental process of Dianthus spp., we performed a comparative analysis of floral morphology and transcriptome dynamics in simple flowers and double flowers. We found that the primordium of double flowers of ‘X’ was larger in size compared to that of simple flowers of ‘L’ in Dianthus chinensis. RNA-seq and Weighted Gene Co-expression Network Analysis (WGCNA) during flower development, identified stage-specific gene network modules. Expression analysis by RNA-seq indicated that a group of genes related to floral meristem identity, primordia position and polarity were highly expressed in double flowers genotypes compared to simple flowers genotypes, suggesting their roles in double-petal formation. A total of 21 DEGs related to petal number were identified between simple and double flowers. The experiments of in situ hybridization revealed that DcaAP2L, DcaLFY and DcaUFO genes were expressed in the intra-sepal boundary and petal boundary. We proposed a potential transcriptional regulatory network for simple and double flower development. This study provides novel insights into the molecular mechanism underlying double flower formation in Dianthus spp.

Characterization of B- and C-class MADS-box genes in medicinal plant <i>Epimedium sagittatum</i>

The basal eudicot Epimedium (Barrenwort) exhibits innovative floral morphology in the form of petal spurs filled with nectar and petaloid sepals. The B-class MADS-box genes <italic>APETALAS3</italic> (<italic>AP3</italic>) and <italic>PISTILLA</italic> (<italic>PI</italic>) determine sepal and petal identity while the C-class gene <italic>AGAMOUS</italic> (<italic>AG</italic>) determines carpel and stamen identity in <italic>Arabidopsis</italic>. Complex histories of gene duplication resulted in subsequent subfunctionalization or neofunctionalization of paralogs. Here, a total of four B- and two C-class genes were successfully isolated from <italic>E. sagittatum</italic>. Phylogenetic analysis showed that <italic>EsAP3-1</italic>, <italic>EsAP3-2</italic>, and <italic>EsAP3-3</italic> are part of the AP3 clade; <italic>EsPI</italic> is part of the PI group; and <italic>EsAG</italic> and <italic>EsAG11</italic> clustered into the AG and AG11 groups, respectively. Quantitative real-time PCR was utilized to detect the expression patterns of these genes, and all B-class genes except for <italic>EsAP3-3</italic> were found to be universally expressed. The transcribed <italic>EsAG</italic> and <italic>EsAG11</italic> genes were confined to reproductive organs. In addition, yeast three and two hybrid assays were used to explore the status of protein complexes. EsAP3-1 was found to have broadly interactive partners, and EsPI can form a heterodimer with EsAP3-1 and EsAP3-2. Transgenic EsAG overexpression in wild-type Arabidopsis confirmed the conserved function determining carpel development.

Alexey Borisovich Shipunov. 9 April 1965 – 4 December 2022

Alexey Borisovich Shipunov. 9 April 1965 – 4 December 2022

Are the floral morphology and anatomy of Galphimia australis, an atypical neotropical Malpighiaceae, associated to a new pollination syndrome?

The flowers of the species of Malpighiaceae in the Neotropical Region are relatively uniform in their morphology due to their dependence on oil-collecting bees as their main pollinators. However, many species of the genus Galphimia seem to have acquired a different floral syndrome, lacking markedly zygomorphic flowers and developed elaiophores in the calyx. Likewise, these species present anthers with great development, probably in response to the selection of pollinators that collect pollen. Galphimia australis incorporated some of these traits but also retained some residual characteristics typical of species pollinated by oil bees. This leads to many questions on how these flowers ensure their pollination. Inquiring about the reduction or modification of these characteristics allows us to understand how G. australis achieves a different pollination syndrome. In this research, we carry out a detailed morphological and anatomical study of the flowers and pollen grain devolvement of G. australis and floral visitors were observed and captured. Results were analyzed in order to determine how this species changed from the oil-floral syndrome, typical of neotropical Malpighiaceae, to one syndrome with pollen as the main reward.

High-resolution transcriptome and volatile assays provide insights into flower development and aroma formation in single- and double-petal jasmines (Jasminum sambac)

Jasmine ( Jasminum sambac ) is one of the most popular ornamental plant species in the world, with diverse floral morphology, including single-petal (SP), double-petal (DP) and multi-petal (MP). Here, based on our recently published chromosome-level genome assemblies of SP and DP Jasmines, we generated high-resolution transcriptional profiles of SP and DP jasmine flowers at six developmental stages and identified key events and regulators contributing to the differences between the two jasmines. The upregulated genes of DP jasmine in early flower development were mainly related to photosynthesis and light reactions, which may contribute to its stronger energy metabolism and environmental adaptability compared with SP jasmine. AGL63 (GOA) and PLETHORA3 (PLT3) motifs involved in floral organogenesis in Arabidopsis were overrepresented at the initial stages in SP and DP, respectively, and may be involved in the development of different petal layers in jasmines. The specific high expression of volatile terpene and benzene/phenylpropane synthesis genes during flowering is an important factor why jasmines during bud development and other tissues are scentless. This factor is also responsible for the typical floral volatiles of jasmine, including terpenes ( α -farnesene, linalool , and ( E )- β -ocimene), and benzenoid lipids (benzyl acetate, methyl salicylate , and methyl benzoate). The high content of α -farnesene and the low content of other core volatiles may constitute the fresh and elegant fragrance of SP compared to DP jasmine. Only DP jasmine had high expression of benzoic acid/salicylic acid carboxyl methyltransferase (BMST), which resulted in its higher content of volatile methyl salicylate and methyl benzoate . Our findings lay the foundation for understanding the flower development and aroma formation mechanisms of different jasmine petal morphologies. • High-resolution transcriptome and volatile assays for single- and double-petal jasmine. • Identified key events and regulators contributing to the differences between two jasmines. • Determine why jasmines were scentless during bud development and other tissues. • The high content of α-farnesene may contribute to the fresh and sweet fragrance of single-petal jasmine. • The expression of BMST was only higher in DP jasmine, resulting in higher content of methyl salicylate and methyl benzoate.

Gene identification and tissue expression analysis inform the floral organization and color in the basal angiosperm Magnolia polytepala (Magnoliaceae).

In Magnolia polytepala, the formation of floral organization and color was attributed to tissue-dependent differential expression levels of MADS-box genes and anthocyanin biosynthetic genes. In angiosperms, the diversity of floral morphology and organization suggests its value in exploring plant evolution. Magnolia polytepala, an endemic basal angiosperm species in China, possesses three green sepal-like tepals in the outermost whorl and pink petal-like tepals in the inner three whorls, forming unique floral morphology and organization. However, we know little about its underlying molecular regulatory mechanism. Here, we first reported the full-length transcriptome of M. polytepala using PacBio sequencing. A total of 16 MADS-box transcripts were obtained from the transcriptome data, including floral homeotic genes (e.g., MpAPETALA3) and other non-floral homeotic genes (MpAGL6, etc.). Phylogenetic analysis and spatial expression pattern reflected their putative biological function as their homologues in Arabidopsis. In addition, nine structural genes involved in anthocyanin biosynthesis pathway had been screened out, and tepal color difference was significantly associated with their tissue-dependent differential expression levels. This study provides a relatively comprehensive investigation of the MADS-box family and anthocyanin biosynthetic genes in M. polytepala, and will facilitate our understanding of the regulatory mechanism underlying floral organization and color in basal angiosperms.

The floral morphology of four Chinese Bambusa species (Poaceae, Bambusoideae) previously described only from vegetative material.

Due to their specialised flowering biology where frequent or even annual flowering is uncommon, reproductive materials of bamboos are not always available, so hampering taxonomic interpretation and research into other aspects. Bambusacontracta, B.corniculata, B.cornigera and B.subtruncata were established only based on vegetative materials and flowering or fruiting material has been hitherto unknown. The floral morphology of these four species is described for the first time and, correspondingly, epitypes are designated to support a more complete interpretation of the species.

A new Octomeria (Orchidaceae: Pleurothallidinae) and nomenclatural notes for related Southern Brazilian species

Octomeria imigiae is proposed as a new species from the Atlantic Rainforest of South Brazil. It is described, illustrated, and compared with sympatric and similar species. An identification key is provided. The new species is recognised by its reptant growth habit and tiny yellow flowers. It is similar to Octomeria chamaeleptotes and several other terete-leaved species from which it can be easily distinguished by its vegetative and floral morphology. Octomeria riograndensis and Octomeria sancti-angeli are proposed as new synonyms of Octomeria chamaeleptotes, and typification designations for this complex are made.

Hemipiliaavisoides (Orchidaceae), a new species from Sichuan Province, China.

A new orchid species, Hemipiliaavisoides, is described from Songpan County and Maoxian County, Sichuan Province, China. Morphologically, H.avisoides is most similar to H.hui, but can be distinguished by the combination of its involute middle lip lobe that is smaller than the lateral lobes, floral bracts that are 5 mm long and are always shorter than the ovary, a leaf that is appressed to the substrate and is adaxially green with white lines along 7-9 principal veins and the subterranean stem with a solitary sheath at its base. The floral morphology of H.avisoides is presented by utilising in vivo micro-CT scanning and 3D visualisation.

The rapid appearance of homostyly in a cultivated distylous population of Primula forbesii.

Evolutionary breakdown from rigorous outbreeding to self-fertilization frequently occurs in angiosperms. Since the pollinators are not necessary, self-compatible populations often reduce investment in floral display characteristics and pollination reward. Primula forbesii is a biennial herb with distribution restricted to southwest China; it was initially a self-incompatible distylous species, but after 20 years of artificial domestication, homostyly appeared. This change in style provides an ideal material to explore the time required for plant mating systems to adapt to new environmental changes and test whether flower attraction has reduced following transitions to selfing. We did a survey in wild populations of P. forbesii where its seeds were originally collected 20 years ago and recorded the floral morph frequencies and morphologies. The floral morphologies, self-incompatibility, floral scent, and pollinator visitation between distyly and homostyly were compared in greenhouse. Floral morph frequencies of wild populations did not change, while the cultivated population was inclined to L-morph and produced homostyly. Evidence from stigma papillae and pollen size supports the hypothesis that the homostyly possibly originated from mutations of large effect genes in distylous linkage region. Transitions to self-compatible homostyly are accompanied by smaller corolla size, lower amounts of terpenoids, especially linalool and higher amounts of fatty acid derivatives. The main pollinators in the greenhouse were short-tongued Apis cerana. However, homostyly had reduced visiting frequency. The mating system of P. forbesii changed rapidly in just about 20 years of domestication, and our findings confirm the hypothesis that the transition to selfing is accompanied by decreased flower attraction.

Ecological niche modeling of interactions in a buzz-pollinated invasive weed

Plant species that are alien and invasive represent an important threat to biodiversity and ecosystem function. These plants compete with native flora for resources and pollinator services. Although most invasive plant species do not depend on pollinators for reproduction and can reproduce uniparentally, some depend on pollinator-assisted reproduction and therefore rely on recruitment of pollinators in the new habitat. Here, we studied Solanum rostratum , a high-risk invasive weed widely distributed around the world that depends on buzz-pollination. It has a floral morphology that depends on medium and large-sized buzzing bees for pollination. The main aim of this study is to model the distribution of an invasive plant, Solanum rostratum, using ecological niches based on its buzz-pollinator distribution. Thus, we hypothesized that S. rostratum is more likely to establish successfully in geographic regions where the appropriate buzz pollinators are also found. We considered the realized and potential distribution of S. rostratum and its pollinators based on occurrence data and ecological niche models combining both abiotic (climatic conditions) and biotic (potential pollinator distribution) factors using the MaxEnt algorithm. Five climatic variables related to temperature and precipitation were important in determining the realized distribution of S. rostratum, while seasonal temperature was the most important variable in determining pollinator distribution. The distributions of the bumblebees ( Bombus fraternus , B. griseocollis , and B. impatiens ) were closely related to the realized distribution of S. rostratum . However, the potential distribution of S. rostratum is wider than that of the pollinator included here, suggesting that other factors such as modifications in the reproductive system or recruitment of other buzzing and non-buzzing bees might be occurring in some invasive populations. We also found that S. rostratum has the potential to expand to unoccupied regions in South America, South Africa, Eastern Europe, and the Middle East. In conclusion, modeling of niches used by invasive species considering both climatic variables and biological interactions such as pollination would be very useful to study and predict the distribution of invasive plants which depend on pollinators to reproduce and establish in new habitats.

Precision Phenotyping of Nectar-Related Traits Using X-ray Micro Computed Tomography.

Flower morphologies shape the accessibility to nectar and pollen, two major traits that determine plant-pollinator interactions and reproductive success. Melon is an economically important crop whose reproduction is completely pollinator-dependent and, as such, is a valuable model for studying crop-ecological functions. High-resolution imaging techniques, such as micro-computed tomography (micro-CT), have recently become popular for phenotyping in plant science. Here, we implemented micro-CT to study floral morphology and honey bees in the context of nectar-related traits without a sample preparation to improve the phenotyping precision and quality. We generated high-quality 3D models of melon male and female flowers and compared the geometric measures. Micro-CT allowed for a relatively easy and rapid generation of 3D volumetric data on nectar, nectary, flower, and honey bee body sizes. A comparative analysis of male and female flowers showed a strong positive correlation between the nectar gland volume and the volume of the secreted nectar. We modeled the nectar level inside the flower and reconstructed a 3D model of the accessibility by honey bees. By combining data on flower morphology, the honey bee size and nectar volume, this protocol can be used to assess the flower accessibility to pollinators in a high resolution, and can readily carry out genotypes comparative analysis to identify nectar-pollination-related traits.