Fertile Stamens Research Articles

Trioecy in <i>Ranunculus auricomus</i> (Ranunculaceae)

Trioecy is here described for the first time in the perennial herbaceous polycarpic Ranunculus auricomus L. (goldilocks buttercup) in the Moscow Region. The study has shown that R. auricomus produces three types of flowers, differing in the structure of both the androecium and gynoecium: perfect flowers (with fertile stamens and carpels), pistillate flowers (complete absence of stamens), and staminate flowers (with fertile stamens and reduced nonfunctional carpels). The perfect flowers and their parts are larger than those of the staminate and pistillate flowers. The seven studied populations included five types of plants, forming: 1) perfect flowers (76.9–80.8% of the total number of generative plants); 2) staminate flowers (2.8–3.9%); 3) pistillate flowers (1.0–3.9%); 4) perfect and staminate flowers (10.8–15.9%); 5) perfect and pistillate flowers (1.0–3.0%). Over the five years of observations (2019–2023), plants of different sexual forms did not change the sex of flowers, and the sex ratio in the populations remained stable, with minor fluctuations.

Floral structure and nectary anatomy of Bertholletia excelsa (Lecythidaceae)

ABSTRACT The floral nectary of Bertholletia excelsa was studied through permanent, histological cross-sections. The flower showed two rings of androecial vascular bundles, the inner for the fertile stamens and the outer for the androecial hood. The androecial hood, originating from the abaxial side of the androecium, is a well-developed, curved, and highly unilateral structure that covers the fertile stamens and stigma. At the apex and on the inner surface of this structure, several finger-like appendages. Histological cross-sections of the androecial hood, from the distal part towards the centre of the flower, reveal that the secretory parenchyma originates in the medium of the inner-distal part of the hood. The secretory tissue is surrounded by vascular bundles that more distally supply the finger-like appendages of the androecial hood. The nectariferous parenchyma lacks internal vascular bundles and consists of small cells, starch-rich, with large vacuoles and a prominent nucleus. The nectariferous epidermis is striated. No stomata or glandular hairs were observed associated with the nectariferous epidermis. The nectary is located within the distal part of the androecial hood and can be classified as a structured, non-vascularized, androecial type. This specialization in the location of the nectar secreting tissue is linked with a complex pollination mechanism, allowing access to the reward only for large bees with long proboscis.

Loss of staminodes in Aquilegia jonesii reveals a fading stamen–staminode boundary

The modification of fertile stamens into sterile staminodes has occurred independently many times in the flowering plant lineage. In the genus Aquilegia (columbine) and its closest relatives, the two stamen whorls closest to the carpels have been converted to staminodes. In Aquilegia, the only genetic analyses of staminode development have been reverse genetic approaches revealing that B-class floral identity genes are involved. A. jonesii, the only species of columbine where staminodes have reverted to fertile stamens, allows us to explore the genetic architecture of staminode development using a forward genetic approach. We performed QTL analysis using an outcrossed F2 population between A. jonesii and a horticultural variety that makes fully developed staminodes, A. coerulea ‘Origami’. Our results reveal a polygenic basis for staminode loss where the two staminode whorls are under some level of independent control. We also discovered that staminode loss in A. jonesii is not complete, in which staminode-like traits sometimes occur in the inner fertile stamens, potentially representing a fading boundary of gene expression. The QTLs identified in this study provide a map to guide future reverse genetic and functional studies examining the genetic basis and evolutionary significance of this trait.

Lopezia guerrerensis (Onagraceae, sect. Lopezia), a new species from the State de Guerrero, México

Lopezia guerrerensis is described as a new species for the flora of the state of Guerrero, Mexico. It is similar to the species of the Lopezia miniata complex, but is distinguished from them by its habit (subshrubs or shrubs to 3.5 m tall), whorled leaves (three per node) with brochidodromous venation and 12–14 (–17) secondary veins per side, flowers with larger lower petals and a longer fertile stamen, and inflorescences in corymbiform racemes, these axillary or grouped together in terminal panicles. For section Lopezia and the tribe Lopeziae, two new characters are added: whorled leaves (three per node) and whorled inflorescences.

Rediscovery and amended description of Strobilanthes humilis (Acanthaceae)

Strobilanthes Blume consists of approximately 350 species, chiefly distributed in the tropical and sub-tropical parts of Asia but extending to the Pacific islands. Approximately 150 species of Strobilanthes are reported from India and, among them, around 70 species are restricted to South India. In the course of a floristic survey in the Megamalai Hills of Tamilnadu in 2016–2017, we collected a remarkable specimen of Strobilanthes, which was characterized by having viscous uninterrupted spikes with a subventricose corolla. Since it has spicate inflorescences, 5-partite calyces, two fertile stamens, and densely hygroscopic-pubescent seeds, the material belongs to the S. kunthiana group. After a critical examination of relevant literature and herbarium materials it was found that the specimen matches the type of S. humilis, hence our collections are the first verified collection after its type collections in 1836.

The role of PCD in sexual dimorphism of dioecious Spinacia oleracea L.

The formation of non-hermaphroditic, i.e. male or female, flowers is a rare event in the plant kingdom. S. oleracea provides an ideal unisexual floral developmental system for studying the structural development of floral organs. These species forms non-hermaphroditic flowers; the pistil is fertile in the female flower, but the development of the stamens stops at an early phase and this organ atrophies and becomes functionless, while the male flowers form four fertile stamens, however there is not any trace of the pistil, it aborts at a much early stage. We searched for the presence of programmed cell death (PCD) in the abortive tissues during the ontogenetic development of these flowers. These results show curicial information on how the fertile sex organ in spinach differentiates and develops while arresting the development of the other aborted sex organ ; the presence of PCD occur in unisexual flower development in rhe very early stage and continue short time. We also found that stamen development in the female flower and pistil development in the male flower were subject to changes that did not result in large-scale structural changes. The PCD data obtained are the first study of spinach in the literature. This type of studies are shedding additional light on the sexual specialization hypothesis. Moreover, the ability to manipulate or control the flowering of the dioecious plant by simple means holds great potential, both from an economic aspect and to increase food production for an ever-growing human population

How do fertile stamens and staminodes go differently in Kingdonia uniflora? Evidence from stamen numbers, ontogeny, and structure

Kingdonia uniflora is in Circaeasteraceae and has fertile stamens and staminodes which are both variable in number; however, the differentiating process of these two types of stamens and the nectariferous structure of staminodes are still unclear. Variation in number and ontogeny (including the degeneration stage of staminodes) of stamens in K. uniflora are investigated under SEM, TEM and LM. The results indicate that there are 63 floral formulas in 80 flowers counted, and the most frequent flower floral formula (4 flowers) is P5A°11A5G6. The correlation between the stamen number and the total floral organ number is high (0.61), while the highest correlation with the total number of floral organs is the number of carpels, and there is a weak correlation between the two types of stamens (-0.23). The stamen development period is divided into five stages, with differentiation of stamens occurring at stage 2. The anther wall formation of fertile stamens is of the basic type, and the simultaneous meiosis form tetrahedral tetrads, while mature pollens are 2-celled and tricolpate. Sporogenous tissue of staminodes fails to develop further at an earlier stage, without the formation of secondary sporogenous cells. The head of mature staminodes has nectary tissue consisting of the secretory epidermis (two types of secretory cells), nectary parenchyma (about 15 layers) and vascular tissue with vessel and sieve tube elements. There are well-developed microchannels in epidermal cell walls, and the cells related to secreting nectar are rich in mitochondria, endoplasmic reticula and small vesicles. In addition, microsporogenesis, male gametophyte development, the secretory function of staminodes, and other characteristics in K. uniflora are similar to those in Ranunculaceae. This study clarifies the differentiating stage of fertile stamens and staminodes and explores the new structure (nectary) that staminodes formed, and also, it enriched the secretion modes in Ranunculales.

HD-ZIP Transcription Factors and Brassinosteroid Signaling Play a Role in Capitulum Patterning in Chrysanthemum.

Chrysanthemum is a genus in the Asteraceae family containing numerous cut flower varieties with high ornamental value. It owes its beauty to the composite flower head, which resembles a compact inflorescence. This structure is also known as a capitulum, in which many ray and disc florets are densely packed. The ray florets are localized at the rim, are male sterile, and have large colorful petals. The centrally localized disc florets develop only a small petal tube but produce fertile stamens and a functional pistil. Nowadays, varieties with more ray florets are bred because of their high ornamental value, but, unfortunately, this is at the expense of their seed setting. In this study, we confirmed that the disc:ray floret ratio is highly correlated to seed set efficiency, and therefore, we further investigated the mechanisms that underlie the regulation of the disc:ray floret ratio. To this end, a comprehensive transcriptomics analysis was performed in two acquired mutants with a higher disc:ray floret ratio. Among the differentially regulated genes, various potential brassinosteroid (BR) signaling genes and HD-ZIP class IV homeodomain transcription factors stood out. Detailed follow-up functional studies confirmed that reduced BR levels and downregulation of HD-ZIP IV gene Chrysanthemum morifolium PROTODERMAL FACTOR 2 (CmPDF2) result in an increased disc:ray floret ratio, thereby providing ways to improve seed set in decorative chrysanthemum varieties in the future.

Strobilanthes sripadensis, a new species of Acanthaceae from Sri Lanka

Strobilanthes sripadensis, a new species of Acanthaceae from Peak Wilderness Nature Reserve, Sri Lanka is described and illustrated. Both morphological and palynological evidence clearly indicate that S. sripadensis is a distinct species. The new species is closely related to S. pentandra, but differs by having short acuminate leaf apex, entire or slightly sinuate leaf margin, 5–7 pairs of lateral veins, outermost bract longer than the inner one, bract, bracteole, and calyx pubescent, white corolla with prominent dark purple lines at throat and fertile stamens 4.The full description, line drawings, photographs, and information on habitat and ecology, distribution, phenology are also provided. It is accessed to be Critically Endangered according to the IUCN Red List categories and criteria.

SEXUAL POLYMORPHISM OF <i>RANUNCULUS CASSUBICUS</i> (RANUNCULACEAE) IN MOSCOW REGION

For the first time, gynodioecy is described in a perennial herbaceous polycarpic plant Ranunculus cassubicus L. (Kashubian buttercup) in the Moscow Region. It was revealed that R. cassubicus forms three types of flowers differing in the androecium structure: perfect (with fertile stamens and carpels), partially male-sterile (the number of stamens varies greatly and is much less than in perfect flowers), and pistillate ones (stamens completely missing). The sizes of flowers and their parts decrease in many studied parameters in the following row: perfect – partially male-sterile – pistillate. The studied 12 populations included six types of individuals forming: 1) only perfect flowers (83.1–89.2% of the total number of generative plants); 2) perfect and partially male-sterile flowers (4.0–6.5%); 3) only partially male-sterile flowers (2.8–3.9%); 4) perfect and pistillate flowers (1.4–2.6%); 5) pistillate and partially male-sterile flowers (1.2–2.9%); 6) only pistillate flowers (0.6–1.5%). It is established that over three years of observations (2020–2022), individuals of different sexual forms did not change the sex of flowers, and the sexual structure of populations remained stable, without sharp fluctuations.

SEXUAL POLYMORPHISM OF <i>RANUNCULUS ACRIS</i> (RANUNCULACEAE) IN THE MOSCOW REGION

The gynodioecy of the polycarpic Ranunculus acris L. was studied in the Moscow Region. This plant has three types of flowers that differ in androecium structure: perfect flowers (with fertile stamens and carpels), partially male-sterile ones (some of the stamens become staminodes to form sterile pollen), and pistillate ones (an extreme reduction of stamens and the complete absence of fertile pollen). These three types of flowers form a size gradient from the largest perfect to the smallest pistillate ones. Each flower type is formed on separate plants. The share of plants with perfect flowers in 10 studied coenopopulations varied from 43.9 to 53.0%, that of the plants with partially male-sterile flowers from 45.5 to 54.4%. Plants with pistillate flowers are extremely rare (1.5–2.0%). Over three years of observations (2020–2022), we found that the sexual forms of the plants did not change the sex of their flowers, and the sex ratio in the coenopopulations remained stable, without significant fluctuations.

Correlation between Inflorescence Architecture and Floral Asymmetry-Evidence from Aberrant Flowers in Canna L. (Cannaceae).

Floral symmetry studies often focus on the development of monosymmetric and polysymmetric flowers, whereas asymmetric flowers and their position and function within the inflorescence structure are largely neglected. Cannaceae is one of the few families that possesses truly asymmetric flowers, serving as a model to study the characters and mechanisms involved in the development of floral asymmetry and its context within the developing and mature inflorescence. In this study, inflorescence structure and floral morphology of normal asymmetric flowers and 16 aberrant flower collections from Canna indica L. and C. glauca L. were photographed, analyzed, and compared with attention to stamen petaloidy, floral symmetry, and inflorescence branching patterns anterior and posterior to the aberrant flower. In comparison with normal flowers, the aberrant flowers are arranged into abnormal partial florescences, and vary in floral symmetry, orientation, and degree of androecial petaloidy. The appendage of the fertile stamen is universally located distal from the higher order bract, indicating an underlying influence of inflorescence architecture. A synthetic model is proposed to explain the relationship between floral symmetry and inflorescence structure. Data from the observation of aberrant phenotypes strongly support the hypothesis that irregular petaloidy of the stamens is correlated with an asymmetric morphogenetic field within the inflorescence that contributes to the overall floral asymmetry in Canna flowers.

Dichorisandra rigidifolia (Commelinaceae), a new species from Cerrado of Goiás, Brazil

Dichorisandra rigidifolia, a new species of the genus and probably endemic to the Cerrado Phytogeographic Domain, is described and illustrated here. Comments on its habitat, distribution, phenology, and conservation status are provided, as well as information concerning its morphological relationships with similar congeners. The new species can be recognized by its erect habit, leaves firmly chartaceous, bracts of the cincinni and bracteoles persistent, flowers with petals lilac or pinkish from the middle third, androecium with six fertile stamens, the thecae lilac or pink with two apical pores, as well as globose, blackish, and smooth capsules.

Diverse function of the PISTILLATA, APETALA 3, and AGAMOUS-like MADS-box genes involved in the floral development in Alpinia hainanensis (Zingiberaceae)

Zingiberaceae is the vital clue and key node in the decreased process of fertile stamens in Zingiberales, helping to understand the evolution of the ginger families. This study focuses on Alpinia hainanensis to investigate the function of B- and C-class MADS-box genes in floral development. The introns size of two B-class genes AhPI and AhAP3, and one C-class gene AhAG are quite variable. By contrast, the positions of the corresponding introns are conserved, resulting in a similar exon size in homologs. The typical region 70 bp-CCAATCA element was not found in the second intron of AhAG compared to AG homologs. The subcellular localization showed that AhAP3 was in both intranuclear and extranuclear. The heterodimer was formed between APETALA3 and PISTILLATA but not between the B- and C-class proteins using Y2H and BiFC. The 35S::AhAG heterologous transformed Arabidopsis had curly and smaller rosette leaves with early flowering. Floral organs had no homeotic conversion, albeit sepals and petals reduced in size. Siliques development was affected and displayed wrinkled and shorter. By contrast, 35S::AhAP3 and 35S::AhPI did not show any modified phenotype in transgenic Arabidopsis thaliana. We first proposed the model for Alpinia flower development. MADS-box transcription factor binding at particular genomic locations and interaction with partners may be crucial for the development of the floral organ.

Terniopsisyongtaiensis (Podostemaceae), a new species from South East China based on morphological and genomic data.

The new species Terniopsisyongtaiensis X.X. Su, Miao Zhang & Bing-Hua Chen, from Fujian Province, China, is described and illustrated. It is similar to T.heterostaminata from Thailand, but differs in its two fertile stamens, fewer but longer vegetative ramuli, fewer but shorter flowering ramuli, shorter pedicels, capsule-stalk and stamens. The complete chroloplast genome of the new species is 129,074 bp long and has a typical quadripartite structure, including two inverted repeat regions (IRs) of 18,504 bp in length, separated by a large single-copy (LSC) and a small single-copy (SSC) regions of 79,000 bp and 13,066 bp, respectively. The ycf1 and ycf2 genes were lost compared to most higher plants, leading to a substantial reduction in the IR. The phylogenetic analysis using both matK and nrITS revealed that T.yongtaiensis is sister to T.heterostaminata with moderate support, and formed a clade with other Terniopsis species, suggesting that the new species belongs to Tristichoideae.

Development and structure of four different stamens in Clematis macropetala (Ranunculaceae): particular emphasis on staminodes and staminal nectary.

The stamens of angiosperms are diverse in number, colour and structure. The morphological and structural changes of stamens show important evolutionary significance for improving pollination efficiency. In Clematis macropetala, the androecium consists of fertile stamens and tepaloid staminodes. However, studies on the developmental features, structures and possible functions of stamens are few. In this study, the stamen ontogeny, micromorphology and nectary structure of C. macropetala were studied by scanning electron microscopy, light microscopy and transmission electron microscopy. The results indicate that the stamens can be divided into four forms according to shape and anther size: tepaloid staminode (St1), spatulate staminode (St2), linear-spatulate fertile stamen (St3) and linear fertile stamen (St4). The characteristics of stamen development are similar in the early stage but gradually differentiate in the later stage. St1 has delayed development and no anther differentiation. St2 develops abnormally at the early stage of anther differentiation. St3 and St4 are fertile, but their anther sizes are different. Nine epidermal cell types were observed in stamens, with only 4 types in St1 and 6-7 types in St2, St3 and St4. Nectary tissue appears on the adaxial side of the filament base. The nectary is composed of only one layer of secretory epidermal cells, which have a large nucleus, dense cytoplasm and well-developed wall ingrowth. Nectar is released through micro-channels in the cuticle of the outer wall. In Ranunculaceae, the staminal nectary is often located on fertile or sterile stamens, and the position, structure and micromorphology of secretory tissues of the stamen within Ranunculales are discussed.

Asymmetric expression patterns of B- and C-class MADS-box genes correspond to the asymmetrically specified androecial identities of Canna indica.

Canna indica is a common ornamental plant with asymmetric flowers having colourful petaloid staminodes. The only fertile stamen comprises a one-theca anther and a petaloid appendage and represents the lowest stamen number in the order Zingiberales. The molecular mechanism for the asymmetric androecial petaloidy remains poorly understood. Here, we studied the identity specification in Canna stamen. We observed four types of abnormal flower in terms of androecium identity transformation and analysed the corresponding floral symmetry changes. We further tested the expression patterns of B- and C-class MADS-box genes using in situ hybridization in normal Canna stamen. Homeotic conversions in the androecium were accompanied by floral symmetry changes, and the asymmetric stamen is key in contributing to the floral asymmetry. Both B- and C-class genes exhibited higher expression levels in the anther primordium than in other androecial parts. This asymmetric expression pattern precisely corresponded to the asymmetric identities of the Canna androecium. We identified C. indica as a model species for studying androecial organ identity and floral symmetry synthetically in Zingiberales. We hypothesized that homeotic genes specify floral organ identity in a putative dose-dependent manner. The results add to the current understanding of organ identity-related floral symmetry.

<p><strong><em>Beilschmiedia osacola</em> (Lauraceae) a new species from the Osa Peninsula, Costa Rica</strong></p>

We describe and illustrate a new species of Beilschmiedia, from the Osa Peninsula of Costa Rica. It is distinguished by its small flowers, which are turbinate to campanulate, with six fertile stamens and pubescent ovary, in addition it has alternate leaves along the twigs, with the lower leaf surface glabrous and not glaucous. In the field, it can be recognized by its stature, a very large tree, with the bark reddish, and peeling in large plates. Among described congeners it is superficially similar to B. hexanthera, from French Guiana, which also has six fertile stamens, and staminodes of whorl III columnar, but differs in having a pubescent ovary and larger, more branched inflorescences.

Expression and Function Studies of CYC/TB1-Like Genes in the Asymmetric Flower Canna (Cannaceae, Zingiberales).

The asymmetric flower, lacking any plane of symmetry, is rare among angiosperms. Canna indica L. has conspicuously asymmetric flowers resulting from the presence of a half-fertile stamen, while the other androecial members develop as petaloid staminodes or abort early during development. The molecular basis of the asymmetric distribution of fertility and petaloidy in the androecial whorls remains unknown. Ontogenetic studies have shown that Canna flowers are borne on monochasial (cincinnus) partial florescences within a racemose inflorescence, with floral asymmetry likely corresponding to the inflorescence architecture. Given the hypothesized role of CYC/TB1 genes in establishing floral symmetry in response to the influence of the underlying inflorescence architecture, the spatiotemporal expression patterns of three Canna CYC/TB1 homologs (CiTBL1a, CiTBL1b-1, and CiTBL1b-2) were analyzed during inflorescence and floral development using RNA in situ hybridization and qRT-PCR. In the young inflorescence, both CiTBL1a and CiTBL1b-1 were found to be expressed in the bracts and at the base of the lateral florescence branches, whereas transcripts of CiTBL1b-2 were mainly detected in flower primordia and inflorescence primordia. During early flower development, expression of CiTBL1a and CiTBL1b-1 were both restricted to the developing sepals and petals. In later flower development, expression of CiTBL1a was reduced to a very low level while CiTBL1b-1 was detected with extremely high expression levels in the petaloid androecial structures including the petaloid staminodes, the labellum, and the petaloid appendage of the fertile stamen. In contrast, expression of CiTBL1b-2 was strongest in the fertile stamen throughout flower development, from early initiation of the stamen primordium to maturity of the ½ anther. Heterologous overexpression of CiTBL genes in Arabidopsis led to dwarf plants with smaller petals and fewer stamens, and altered the symmetry of mature flowers. These data provide evidence for the involvement of CYC/TB1 homologs in the development of the asymmetric Cannaceae flower.

A novel type of mirror-image flowers caused by lateral bending of the floral tube in a bumblebee-pollinated plant

We studied a previously unreported form of mirror-image flowers in Rhabdothamnopsis sinensis (Gesneriaceae) endemic to China. The style in R. sinensis remains straight throughout the blooming period, while the basal part of the floral tube bends either to the left or right side, causing the style to lean towards the right or left side of the floral tube. R. sinensis has two epipetalous fertile stamens with twisted filaments, moving the fused anthers located at the opposite side of the style. This floral syndrome results in reciprocal mirror-image flowers in a relative simpler way as compared to typical types of mirror-image flowers. Pollinator observations revealed that the bending of the floral tube and twisted filament block the entrance to the floral tube, rendering long-tongued bumblebees as pollinators by transferring pollen with the side of the thorax. R. sinensis is self-compatible and the pollen-ovule ratio is strikingly low (37.41 ± 11.90). Thorax pollination probably is the main reason for such low pollen wastage because the thorax suffers less grooming than the abdomen, which is the main pollen-carrying part in other typical mirror-image flowers. The unusual type of mirror-image flowers described here suggests a specialized pollination adaptation with limited but high-fidelity pollinators.