Antesepalous Stamens Research Articles

Floral development study of <italic>Exochorda</italic> Lindl. reveals new evidence for the evolution of the androecium in Rosaceae

<p indent="0mm">Rosaceae have a unique outer whorl of stamen pairs, numerous stamen whorls, and high morphological and developmental diversity of the androecium. Explanations of the developmental mode of the androecium in Rosaceae are controversial. Linfenhofer and Weber proposed a specific developmental mode of the androecium in Rosaceae called “the spiraeaoid pattern”, but whether this pattern can be used as a general type in Rosaceae remains highly controversial. Additionally, the developmental modes of the specific androecia in some genera are unknown. <italic>Exochorda</italic> has fascicular stamens, which have rarely been reported in Rosaceae, and previous studies have not explained how fascicular stamens are formed in <italic>Exochorda</italic>. Our study used scanning electron microscopy to study floral development in <italic>E</italic>.<italic> racemosa</italic> and <italic>E</italic>.<italic> serratifolia</italic>. The results showed that the disappearance of antesepalous stamens and expansion of the antesepalous hypanthium contributed to the formation of the fascicular stamens. The androecium developmental mode also revises the androecium arrangement of the “spiraeaoid pattern”, and verifies the possibility of repetition of the “spiraeoid pattern” as the developmental basis of polyandry in Rosaceae.

Connective modifications and origin of stamen diversity in Melastomataceae.

The androecium of Melastomataceae presents notable modifications in its merosity, morphology between whorls and in prolonged connectives and appendages. We carried out a comparative study of six Melastomataceae species to shed light on the developmental processes that originate such stamen diversity. The development of stamens was studied using scanning electron microscopy and histological observations. The stamens of all species studied have a curved shape because they emerge on a plane displaced by the perigynous hypanthium. They are the last flower organs to initiate and therefore their growth is inwards and towards the floral center. Despite the temporal inversion between carpels and stamens in Melastomataceae, the androecium maintains the centripetal pattern of development, the antepetalous stamens emerging after antesepalous stamens. The isomerous androecium can be the result of abortion of the antepetalous stamens, whereas heterostemony seems to be caused by differences in position and the stamen development time. Pedoconnectives and ventral appendages originate from the basal expansion of the anther late in floral development. The delay in stamen development may be a consequence of their dependence on the formation of a previous space so that they can grow. Most of the stamen diversity is explained by the formation of the connectives and their appendages. The formation of a basal-ventral anther prolongation, which culminates in the development of the pedoconnective, does not differ from other types of sectorial growth of the connective, which form shorter structures.

A New Species of Comolia (Melastomataceae, Marcetieae) from the Sand Dunes of Bahia, Brazil, with Notes on Leaf Anatomy

Abstract— Comolia abaetensis, an endemic new species from the Abaeté and Itapuã sand dunes, Bahia, Brazil, is described and illustrated. Additionally, field images and a geographic distribution map of the new species are provided, together with morphological and leaf anatomy comparisons among the most similar congeners, and a dichotomous key to the species that occur in Brazil. Comolia abaetensis is morphologically similar to C. ovalifolia, but differs from the latter by the following combination of characteristics: glabrous (rarely with sparse trichomes) internodes and hirsute nodes, glabrous leaf blades or rarely with sparse eglandular trichomes, abaxial surface predominantly red with green nuances, glabrous pedicels, cupuliform hypanthium, and filaments of the antesepalous stamens that are 5‐6 mm long. Specimens of C. abaetensis have been confused with and/or tentatively determined as C. berberifolia. However, these two species are readily distinguished by the size of the leaves, the length of the trichomes and filaments, and the color of the abaxial foliar surfaces. Comparisons between the leaf anatomy of C. abaetensis and C. ovalifolia are provided and the occurrence of emergences and hydathodes are here reported for the genus for the first time. Finally, we informally recommend a conservation status of Critically Endangered [CR B1ab (iv) + 2ab (iv)] for C. abaetensis.

Miconia waimiri-atroari (Miconieae, Melastomataceae): a new species from the Brazilian Amazon Forest

Miconia waimiri-atroari is presented here as a new species from the Brazilian Amazon Forest. This new species has discolorous leaf blades, inflorescences with scorpioid branches, and petals and antesepalous stamen connectives with glandular trichomes. It has been misidentified as Miconia argyrophylla, another species from the Amazon Forest that has this same set of characters. However, the new species has cylindrical young branches (vs. quadrangular in M. argyrophylla), stellate trichomes on leaf abaxial surface (vs. arachnoid), stamens with yellow filaments that turn red in old flowers (vs. stamens with white filaments that only turn pale in old flowers), and style with glandular trichomes (vs. glabrous). At the moment, the species is only known from a small area north of Manaus, state of Amazonas, Brazil. Morphological description, illustrations, general comments and comparison to other similar species are also provided.

Molecular framework underlying floral bilateral symmetry and nectar spur development in Tropaeolum, an atypical member of the Brassicales.

Floral spurs are key innovations associated with elaborate pollination mechanisms that have evolved independently several times across angiosperms. Spur formation can shift the floral symmetry from radial to bilateral, as it is the case in Tropaeolum, the only member of the Brassicales with floral nectar spurs. The genetic mechanisms underlying both spur and bilateral symmetry in the family have not yet been investigated. We studied flower development and morphoanatomy of Tropaeolum longifolium. We also generated a reference transcriptome and isolated all candidate genes involved in adaxial-abaxial differential growth during spur formation. Finally, we evaluated the evolution of the targeted genes across Brassicales and examined their expression in dissected floral parts. Five sepals initiate spirally, followed by five petals alternate to the sepals, five antesepalous stamens, three antepetalous stamens, and three carpels. Intercalary growth at the common base of sepals and petals forms a floral tube. The spur is an outgrowth from the adaxial region of the tube, lined up with the medial sepal. We identified Tropaeolum specific duplications in the TCP3/4L and STM gene lineages, which are critical for spur formation in other taxa. In addition, we found that TM6 (MADS-box), RL2 (RAD-like7), and KN2/6L2 and OSH6L (KNOX1 genes), have been lost in core Brassicales but retained in Tropaeolum. Three genes are pivotal during the extreme adaxial-abaxial asymmetry of the floral tube, namely, TlTCP4L2 restricted to the adaxial side where the spur is formed, and TlTCP12 and TlSTM1 to the abaxial side, lacking a spur.

Hofmeister’s Rule’s Paradox: Explaining the Changeable Carpel Position in Caryophyllaceae

Premise of research. In Caryophyllaceae with a gynoecium isomerous with the other floral whorls, carpels can be in either antesepalous or antepetalous position. Morphologists have long been unable to find a unifying hypothesis to explain the different carpel positions in Caryophyllaceae, as variation in carpel position breaks with Hofmeister’s rule of alternating whorls.Methodology. In this study, we investigate the floral development of six species of Caryophyllaceae with isomerous flowers using scanning electron microscopy to clarify the differences between carpel positions and whether developmental modes are responsible. Special attention is paid to the correlation between the development of carpels and other floral organs.Pivotal results. In Spergula arvensis, Agrostemma githago, and Myosoton aquaticum, carpels are in antepetalous position, while the antesepalous stamens develop more centrally in a sequence inverse to the sepals. In Cerastium glomeratum and Silene diocia, carpels are in antesepalous position, while the antesepalous stamens do not show an inverse development and are inserted almost at the same level as antepetalous stamens. In Lychnis flos-cuculi, the carpels are not clearly in an antesepalous or antepetalous radius, and the development of antesepalous stamens shows a slight unequal growth.Conclusions. Developmental evidence rejects the hypothesis that the developmental modes of carpels are the reason for the different carpel positions. Carpel position is correlated with the developmental sequence of antesepalous stamens and the level of emergence of antepetalous stamens on the floral apex. Space availability and pressure exercised by the sepals is responsible for the unequal development and a more central position of antesepalous stamens, with those opposite the inner sepals developing faster, causing the carpels to shift to an antepetalous position. With greater availability of space, antesepalous stamens initiate simultaneously or continue the sequence of sepal initiation, and all stamens are more or less equidistant from the apex; the antesepalous stamens do not display an inverse development, and the carpels initiate in antesepalous position, which is consistent with Hofmeister’s rule.

Floral morphology and morphogenesis in Sanguisorba (Rosaceae): flower diversification despite petal reduction and spatial constraints

Abstract Most Rosaceae flowers are pentamerous and have petals, but subtribe Sanguisorbinae have small tetramerous (or trimerous) flowers without petals, and their floral morphology and morphogenesis remain poorly known. We investigated the floral development of three Sanguisorba spp. using scanning electron microscopy to clarify the relationship between floral development and mature flowers, with emphasis on floral constraints affecting reduction of petals, diversity of androecial patterns and the development of the gynoecium and ovule, and to clarify the pollination mechanisms in the absence of petals. All species have botryoids, with numerous flowers initiated acropetally, and the maturation of flowers follows different directions. All flowers are tetramerous and sepals emerge pairwise. No petal primordia appear. Antesepalous stamens are initiated in a pairwise manner; only S. hakusanensis has a second whorl. The ovary appears inferior by development of a cystiform hypanthium. There is only one ovule with a single integument by reduction of the inner. The space occupied by the larger sepals forces the stamens to develop sequentially. Our data demonstrate that petals are basically absent and that there is a possible shift of pollination mechanisms in Sanguisorba among the mainly wind-pollinated Sanguisorbinae, as both anemophilous and entomophilous characters are found in this genus.

A New Endangered Species of Fritzschia Cham. (Melastomataceae, Marcetieae) from Espinhaço Range, Minas Gerais, Brazil

Abstract—During a field expedition to the Serra do Cipó, Minas Gerais state, Brazil, we found a new species of Fritzschia, a genus endemic to campos rupestres from the Espinhaço Range. Fritzschia cordifolia has cordate and succulent leaves with an apical gland, petals with glandular-ciliate margin, campanulate hypanthium, and antesepalous stamens with ventral appendages with deltoid lobes. The presence of seeds with a crested testa is reported here for the first time in Fritzschia. A description and illustration of the new species is provided, as well as its conservation status and its geographical distribution.

Microlicia longirostrata, a new species of Melastomataceae from Goiás in central Brazil

Abstract—Microlicia longirostrata (Melastomataceae), a new species from Goiás, is described and illustrated, and a discussion on leaf anatomy is also provided. The new species resembles M. consimilis and M. psammophila, but differs from them in having an indumentum with both short-stalked, spherical, glandular trichomes and long-stalked, glandular emergences, polysporangiate anthers and antesepalous stamens with a very long beak (2‐2.5 mm long), and annular collenchyma on the adaxial region of the midrib.

Nothodissotis (Melastomataceae), a new genus from Atlantic Central Africa, including the new species N.alenensis from Equatorial Guinea.

Based on morphological and phylogenetic evidence, a new genus of Melastomataceae (Melastomateae), Nothodissotis Veranso-Libalah & G.Kadereit, gen. nov., is described from Atlantic Central Africa. Nothodissotis is distinguished from other African Melastomateae genera by its calyx-lobes that are notched at apex and asymmetrical (vs. entire and symmetrical). Nothodissotis includes two species: the type species N.barteri (Hook.f.) Veranso-Libalah & G.Kadereit, comb. nov. (syn. Dissotisbarteri Hook.f.), and the new species N.alenensis Veranso-Libalah & O. Lachenaud, sp. nov., described and illustrated here. Both species are restricted to open vegetation on rock outcrops within the forested region of Atlantic Central Africa. Nothodissotisbarteri has a scattered distribution in Cameroon, Equatorial Guinea, Gabon and Príncipe Island, while N.alenensis is endemic to the Monte Alén massif in Equatorial Guinea, an area where N.barteri does not occur. Nothodissotisalenensis differs from N.barteri by its hypanthium bearing sessile appendages with penicillate hairs (vs. stalked stellate appendages) and its staminal appendages that are much smaller in antepetalous than in antesepalous stamens (vs. subequal in all stamens). The conservation status of both N.barteri and N.alenensis is assessed as Vulnerable in accordance with IUCN criteria.

Floral development and anatomy of

We investigated the floral anatomy and development of Macarthuria australis Hügel ex Endl., an unusual genus endemic to Australia, in the context of floral evolution of core Caryophyllales. Flower initiation is spiral, with sepals developing quincuncially. The first two petals continue the sequence of sepal initiation, but the remaining petals arise from common stamen–petal primordia. The androecium develops sequentially as three inner antesepalous and five outer antepetalous stamens. The globular ovary is trimerous with a short symplicate zone and two arillate ovules per locule. The rapid emergence of the androecium leads to a partial absorption of the petal primordia within the androecial tissue. The two first-formed petals have more room for development and precede the androecium, supporting the fact that petals are not staminodial in origin. This heterochronic shift correlates with an inversed developmental sequence of the antesepalous stamens. The constraint caused by the spatial occupation of sepals and carpels leads to the loss of two stamens, and the re-arrangement of stamens and petals along the flanks of the carpels. The floral development of Macarthuria anticipates a syndrome of stamen and petal development in other core Caryophyllales and culminating in the Caryophyllaceae.

The recognition of Tibouchina setosociliata Cogn. (Melastomataceae, Melastomeae) and its transfer to Pleroma D. Don

Pleroma setosociliatum (Cogn.) F.S. Mey. &amp; F.B. Matos, from the states of Paraná and Santa Catarina, Brazil, has been indicated, still as a name in Tibouchina, as a synonym of T. dubia (Cham.) Cogn. on several floras and electronic databases. However, field observations and a more detailed analysis of herbarium specimens, including the types, led to the conclusion that these two species are distinct. They differ from each other not only in geographic distribuition, but also in growth habit, leaf size, indument, and dimensions of the connectives on antesepalous stamens. Tibouchina setosociliata is here transferred to Pleroma on the basis of morphology and results of a previously published molecular phylogeny.

Geraniales flowers revisited: evolutionary trends in floral nectaries.

The detailed relationships in Geraniales in their current circumscription have only recently been clarified. The disparate floral morphologies and especially the nectaries of the corresponding group have consequently not previously been studied in a phylogenetic context. The present study investigates floral and especially nectary morphology and structure for representatives of 12 of the 13 currently accepted genera in the five families of the Geraniales. Flowers were studied using light microscopy and scanning electron microscopy. The data demonstrate the derivation of even the most disparate floral morphologies from a basic pentamerous and pentacyclic organization, with an obdiplostemonous androecium and receptacular nectaries associated with the antesepalous stamens. Divergent morphologies are explained by modifications of merosity (tetramerous flowers), symmetry (several transitions to zygomorphic flowers) and elaboration of the nectaries into variously shaped outgrowths and appendages, especially in Francoaceae. The divergent development of nectar glands ultimately leads to either a reduction in their number (to one in some Geraniaceae and Melianthaceae) or their total loss (some Vivianiaceae). Floral morphology of the Geraniales shows a high degree of similarity, despite the variation in overall floral appearance and nectary morphology. A hypothesis on the transformation of the nectaries within the Geraniales is presented.

Three new species of Pleroma (Melastomataceae) from Inselbergs of Espírito Santo, Brazil

Three new species of Pleroma are described: Pleroma costatocalyx, P. kollmanniana and P. subsessilis. All three species are morphologically similar to Tibouchina heteromalla and related species, especially due to the shrubby habit, elongated inflorescences, flowers with purple petals, but white at their bases, antesepalous stamens with the connective covered with glandular trichomes, and by the short (ca. 4–5 mm long), curved style. All three species differ from T. heteromalla by the styles with trichomes (vs. glabrous in T. heteromalla). Pleroma costatocalyx also differs from T. heteromalla by the longitudinally costate hypanthium, P. kollmanniana by the strongly winged branches, bigger leaves, and shorter petioles, and P. subsessilis by the concolorous leaves and antepetalous stamens with glabrous connective and appendages. All new species grow in vegetation associated with inselbergs and are endemic to Espírito Santo state, despite the fact that one of them (P. costatocalyx) was collected very close to the border with Minas Gerais, where it probably occurs. We present descriptions, taxonomic comments, illustrations, and conservation status assignments for the new species.

Evidence for Division of Labor and Division of Function Related to the Pollen Release in Papilionoideae (Leguminosae) with a Heteromorphic Androecium

Premise of research. Heterostemony occurs in all three traditional subfamilies of Leguminosae, but it is most commonly found in the Papilionoideae, which are characterized by papilionaceous corollas and complex pollen-releasing mechanisms. Our objective was to evaluate evolutionary and reproductive advantages of heterostemony in papilionoid legumes.Methodology. We investigated the functionality of pollen grains and floral ontogeny of two heterostemonous papilionoid species, Lupinus “The Governor” and Cytisus scoparius, using SEM, LM, and TEM techniques.Pivotal results. Lupinus showed differences in pollen viability between the two stamen morphs. The antesepalous stamens (producing fertile pollen grains) are initiated in reversed unidirectional order and develop before the antepetalous stamens (producing sterile pollen grains). During the development, the keel petals fuse at their ventral and dorsal regions, forming a tube, which surrounds the reproductive column, leaving an apical opening through which th...

Obdiplostemony: the occurrence of a transitional stage linking robust flower configurations.

Obdiplostemony has long been a controversial condition as it diverges from diplostemony found among most core eudicot orders by the more external insertion of the alternisepalous stamens. In this paper we review the definition and occurrence of obdiplostemony, and analyse how the condition has impacted on floral diversification and species evolution. Obdiplostemony represents an amalgamation of at least five different floral developmental pathways, all of them leading to the external positioning of the alternisepalous stamen whorl within a two-whorled androecium. In secondary obdiplostemony the antesepalous stamens arise before the alternisepalous stamens. The position of alternisepalous stamens at maturity is more external due to subtle shifts of stamens linked to a weakening of the alternisepalous sector including stamen and petal (type I), alternisepalous stamens arising de facto externally of antesepalous stamens (type II) or alternisepalous stamens shifting outside due to the sterilization of antesepalous stamens (type III: Sapotaceae). In primary obdiplostemony the alternisepalous stamens arise before the antesepalous stamens and are more externally from initiation. The antesepalous stamen whorl is staminodial and shows a tendency for loss (type I), or the petals are missing and the alternisepalous stamens effectively occupy their space (type II). Although obdiplostemony is often related to an isomerous gynoecium, this is not essential. Phylogenetically, both secondary and primary obdiplostemony can be seen as transitional stages from diplostemony to either haplostemony or obhaplostemony. Obdiplostemony is the consequence of shifts in the balance between the two stamen whorls, affecting either the alternisepalous stamens together with the petals, or the antesepalous stamens. We advocate a broad definition of obdiplostemony, to include androecia with incomplete whorls, staminodial whorls, anisomerous gynoecia and an absence of petals. As such, the taxonomic significance of obdiplostemony is transient, although it is a clear illustration of how developmental flexibility is responsible for highly different floral morphs.

Floral Development of Parkia multijuga and Stryphnodendron adstringens, Two Andromonoecious Mimosoid Trees (Leguminosae)

Premise of research. This study compares the development of staminate and hermaphrodite flowers of Parkia multijuga and Stryphnodendron adstringens, two andromonoecious mimosoid trees, in order to determine whether diclinous flowers result from the same developmental processes. The issues involving the interesting structure of the perianth were also addressed.Methodology. Flowers and flower buds of various sizes were processed for surface and histological observations.Pivotal results. Five sepal primordia emerge in the floral meristem from the abaxial side in a sequential order in P. multijuga and from the adaxial side of the flower in a modified helical order in S. adstringens. Five petal primordia initiated simultaneously in P. multijuga and S. adstringens. The carpel primordium initiates concomitantly with five antesepalous stamen primordia in P. multijuga and after petal elongation in S. adstringens. All connections among floral organs in P. multijuga (gamosepaly, gamopetaly, epipetaly, and staminal tube) and S. adstringens (gamosepaly and gamopetaly) are postgenital. A sixth sepal primordium found in some S. adstringens flowers is formed late in the development. Early ontogenetic stages are similar between hermaphrodite and staminate flowers of both species, and only in middevelopmental stages does the carpel primordium stop elongating; no ovule, style, or stigma is formed, leaving only a small carpellodium in the center of the staminate flowers.Conclusions. Our ontogenetic studies show that carpel abortion, not carpel absence from inception, results in staminate flowers in two andromonoecious legumes.

The significance of meristic changes in the flowers of Sapotaceae

Sapotaceae belongs to the heterogeneous order Ericales and exhibits extensive diversity in floral morphology. Although pentamery is widespread and probably the ancestral condition, some clades are extremely variable in merism, with fluctuations between tetramery to hexamery and octomery, affecting different floral organs to different degrees. We assessed the different states of merism in Sapotaceae to determine the evolution of this character among different clades. The floral morphology and development of nine species from eight genera were investigated using scanning electron microscopy (SEM). Furthermore, floral characters related to merism were mapped onto a phylogenetic tree to analyse the distribution and evolutionary significance of merism in the family. Developmental evidence shows that changes in merism are linked to a concerted multiplication of organs among whorls and an increase in whorls through the displacement of organs. Although pentamery is reconstructed as the ancestral condition, a reduction to tetramery or an increase to a higher merism (mainly hexamery or octomery) has evolved at least five times in the family. Fluctuations in merism between different whorls are not random but occur in a coordinated pattern, presenting strong synapomorphies for selected clades. Octomery has evolved at least twice, in Isonandreae from tetramery and in Sapoteae-Mimusopinae from pentamery. Hexamery has evolved at least three times, independently in Northia, the Palaquium clade of Isonandreae and derived from octomery in Sapoteae-Mimusopinae. Three possibilities of merism increase have been identified in Sapotaceae: (1) a concerted increase affecting all organs more or less equally (Palaquium clade of Isonandreae, Sapoteae); (2) a coordinated increase in petals, stamens and mostly carpels without effect on sepals (Labourdonnaisia,Payena–Madhuca clade of Isonandreae); (3) an increase in carpels independently of other organs (Burckella,Letestua,Labramia, etc.). A major shift affecting all Sapotaceae, except Isonandreae, is the sterilization or loss of the antesepalous stamen whorl. The presence of two fertile stamen whorls in Isonandreae indicates a possible reversal or a retained plesiomorphy. In a number of genera, stamens are secondarily increased independently of changes in merism. Descriptions of flowers listing only organ numbers are thus misleading in the inference of evolutionary relationships, as they do not differentiate between changes in merism affecting the number of perianth whorls and other changes affecting the androecium, such as sterilization, loss or occasional doubling of antepetalous stamens.

Three new endangered species of Trembleya DC. (Melastomataceae: Microlicieae) from Minas Gerais, Brazil

During the preparation of a monograph of Trembleya DC. (Melastomataceae) three new species were found that are here described and illustrated: Trembleya acuminata can be recognized by its ovate and vernicose leaves with an acuminate-cuspidate apex, 6-merous flowers, and 4-locular ovary. Trembleya botaensis and Trembleya thomazii are closely related, differing by the indumentum with only sessile glands, white/purple colored petals, calyx lobes without a glandular apical seta, and by the apically rounded connective of the antesepalous stamens in Trembleya thomazii.

Pterolepis haplostemona (Melastomataceae): a new serpentine endemic from Goiás, Brazil

Pterolepis haplostemona from ultramafic outcrops in Goiás, Brazil is described, illustrated, and compared with presumed relatives, all of which are also endemic to Brazil. It is distinguished by its annual habit, simple hypanthial trichomes and intercalycine emergences, haplostemonous flowers, rostrate antesepalous stamens, short pedoconnective, linear-lanceolate cauline leaf blades, calyx lobes tipped with a rigid unbranched trichome, and 3-4-locular ovary. This species and Microlicia macedoi appear to be the only known Melastomataceae that are endemic to serpentine substrates in Brazil. A conservation assessment based on IUCN criteria is also provided.