Polygamy in Atriplex halimus L. (Chenopodiaceae)

It appears that up to now the inflorescence and flower morphologies of Atriplex halimus have been described incompletely. This species has been classified as monoecious or dioecious. Numerous observations and ontogenic studies have pointed to types of flowers morphologically and functionally hermaphroditic, never described until now. One specimen of this species presents both unisexual, male and female flowers and bisexual flowers, so Atriplex halimus is polygam and more precisely trimonoecious. Observation of inflorescences reveals a structure based on the spike and the dichasium. The sex distribution along the inflorescence axis was studied and the existence of a physiological gradient controlling its expression is discussed.     

Diversity and evolution of pollinator rewards and protection by <Emphasis Type="Italic">Macaranga</Emphasis> (Euphorbiaceae) bracteoles

Flowering plants have modified their floral organs in remarkably diverse ways to optimize their interaction with pollinators. Although floral organs represent a major source of floral diversity, many plants also use extrafloral organs, such as bracts and bracteoles, in interacting with pollinators; however, the evolutionary dynamics of non-floral organs involved in pollination are poorly studied. The genus Macaranga is characterized by protective mutualisms with ants that potentially interfere with pollinators on flowers. Macaranga flowers lack perianths and, notably, bracteoles serve the dual function of rewarding pollinators and protecting them from guarding ants; in one group of species, bracteoles provide a nectar reward to generalist pollinators, while in another group, bracteole “chambers” protect thrips or hemipteran pollinators that use these structures as feeding and breeding sites. We examined the diversity and evolutionary dynamics of inflorescence morphology in Macaranga, focusing on bracteoles. We recognized three inflorescence types based on examination of herbarium materials: Discoid-gland, which possess disc-shaped glands on the bracteole surfaces (including all the generalist-pollinated species); Enclosing, in which bracteoles cover flowers (including all the thrips- and hemipteran-pollinated species); and Inconspicuous, in which bracteoles are small, narrow or absent. Ancestral state reconstruction indicated that inflorescence morphologies have changed multiple times in the genus. These findings suggest that morphological changes in non-floral characters (bracteoles) of Macaranga species have occurred as frequently as in the floral structures of many flowering plants. The multiple evolutions of the Enclosing bracteoles, which protect pollinators, might have been facilitated by pollination interference from mutualistic ants.     

The need to re-investigate the nature of homoplastic characters: an ontogenetic case study of the 'bracteoles' in Atripliceae (Chenopodiaceae)

Background and Aims

Within Chenopodioideae, Atripliceae have been distinguished by two bracteoles enveloping the female flowers/fruits, whereas in other tribes flowers are described as ebracteolate with persistent perianth. Molecular phylogenetic hypotheses suggest ‘bracteoles’ to be homoplastic. The origin of the bracteoles was explained by successive inflorescence reductions. Flower reduction was used to explain sex determination. Therefore, floral ontogeny was studied to evaluate the nature of the bracteoles and sex determination in Atripliceae.

Methods

Inflorescences of species of Atriplex, Chenopodium, Dysphania and Spinacia oleracea were investigated using light microscopy and scanning electron microscopy.

Key Results

The main axis of the inflorescence is indeterminate with elementary dichasia as lateral units. Flowers develop centripetally, with first the formation of a perianth primordium either from a ring primordium or from five individual tepal primordia fusing post-genitally. Subsequently, five stamen primordia originate, followed by the formation of an annular ovary primordium surrounding a central single ovule. Flowers are either initially hermaphroditic remaining bisexual and/or becoming functionally unisexual at later stages, or initially unisexual. In the studied species of Atriplex, female flowers are strictly female, except in A. hortensis. In Spinacia, female and male flowers are unisexual at all developmental stages. Female flowers of Atriplex and Spinacia are protected by two accrescent fused tepal lobes, whereas the other perianth members are absent.

Conclusions

In Atriplex and Spinacia modified structures around female flowers are not bracteoles, but two opposite accrescent tepal lobes, parts of a perianth persistent on the fruit. Flowers can achieve sexuality through many different combinations; they are initially hermaphroditic, subsequently developing into bisexual or functionally unisexual flowers, with the exception of Spinacia and strictly female flowers in Atriplex, which are unisexual from the earliest developmental stages. There may be a relationship between the formation of an annular perianth primordium and flexibility in floral sex determination.     

Floral ontogeny in <Emphasis Type="Italic">Astragalus compactus</Emphasis> (Leguminosae: Papilionoideae: Galegeae): variable occurrence of bracteoles and variable patterns of sepal initiation

Comparative studies of floral ontogeny represent a growing field that promise to provide new insights on floral evolution. Floral ontogenetic information has been used successfully in Leguminosae for re-examining phylogenetic relationships at different levels. Using epi-illumination light microscopy, we present original ontogenetic data in Astragalus compactus, which was chosen because of its unusual arrangement of inflorescence and variable occurrence of bracteoles on flowers. Based on our results, uncommon ontogeny of the inflorescence led to the arrangement of flowers in four different positions. Variation was observed not only in the presence of bracteoles, but also in the order of sepal initiation in flowers of the same inflorescence. Surprisingly, besides the widely stated unidirectional pattern, bidirectional, sequential and an atypical unreported order were observed. High degree of overlapping between whorls and formation of two types of common primordia also were found. The variable occurrence of bracteoles suggests that the species is in an intermediate state towards fully lacking of bracteoles. We propose that the variability of the sequence of sepal initiation is possibly a consequence of the function of mechanical forces generated by surrounding leaves. Relationships between mechanical force and auxin signalling are discussed.     

The arrangement of Sepals and Petals in Parnassia palustris L.

The aestivation of the calyx and corolla in 640 flower budsof Parnassia palustris L. from two sites in Britain is recorded. Only two types of calyx arrangement are found. They are quincuncial,one being the mirror-image of the other and they continue thespiral from the bracteoles in the left or right direction respectively.The two types occur in almost equal numbers. Twenty-two of the possible thirty-two corolla arrangements arefound and there is a predominance of apotactous forms. The convolutecorolla does not occur. The three commonest corolla types foundin flowers with a right calyx are respectively the mirror-imagesof the three commonest corolla types in flowers with a leftcalyx. Corolla arrangements differing greatly from the six commontypes are rare. Although the completely eutopic corollas arenot found, the commonest types are strongly eutopic and thereis a highly significant tendency to eutopy in each sample asa whole. In flowers of each calyx type the overlaps betweenthe two posterior petals and on the ß-bracteole sideof the flower are predominantly eutopic whereas the two overlapson the -bracteole side involving petal 9 are nearly always metatopic. These observations are compared with those made on other specieswith variably imbricate pentamerous corollas and their significanceis briefly discussed.     

A new species of Oryctina (Loranthaceae) from Guyana

A new species ofOryctina (Loranthaceae) from Guyana,O. atrolineata Kuijt is described and illustrated. It possesses one-flowered inflorescences, the flowers being hexamerous and each subtended by a bract and two minute bracteoles. A peculiarity of the style is a distinctive fusiform, subterminal swelling.Oryctina atrolineata is closely related, and similar to,O. myrsinites (Eichler) Kuijt.     

Phylogeny and evolution of bracts and bracteoles in Tacca (Dioscoreaceae)

Most species in the genus Tacca (Dioscoreaceae) feature green to black purple, conspicuous inflorescence involucral bracts with variable shapes, motile filiform appendages (bracteoles), and diverse types of inflorescence morphology. To infer the evolution of these inflorescence traits, we reconstructed the molecular phylogeny of the genus, using DNA sequences from one nuclear, one mitochondrial, and three plastid loci (Internal Transcribed Spacer (ITS), atpA, rbcL, trnL-F, and trnH-psbA). Involucres and bracteoles characters were mapped onto the phylogeny to analyze the sequence of inflorescence trait evolution. In all analyses, species with showy involucres and bracteoles formed the most derived clade, while ancestral Tacca had small and plain involucres and short bracteoles, namely less conspicuous inflorescence structures. Two of the species with the most elaborate inflorescence morphologies (T. chantrieri in southeast China and T. integrifolia in Tibet), are predominantly self-pollinated, indicating that these conspicuous floral displays have other functions rather than pollinator attraction. We hypothesize that the motile bracteoles and involucres may facilitate selfing; display photosynthesis in the dim understory, and protect flowers from herbivory.     

Taxonomic position and distribution of Atriplex lapponica (Chenopodiaceae)

The arctic, halophytic species Atriplex lapponica Pojark has flowers of two kinds: perfect ones surrounded by a pentamerous perianth and pistillate flowers enclosed in bracteoles. Thus, A. lapponica is closely related to the species of sect. Dichospermum Dumort, not to species of sect. Teutliopsis Dumort. as generally believed.     

Pollen-stigma interference in two gynodioecious species of Lamiaceae with intermediate individuals

BACKGROUND AND AIMS: Intermediate individuals (perfect flowers with very high degree of pollen abortion) in a gynodioecious plant species are very rare. A study is made of male-female relationships in each flower type and how floral characters can enhance the avoidance of 'pollen discounting' and 'self-pollination' in two gynodioecious species, Teucrium capitatum and Origanum syriacum. METHODS: The relationship between stigma receptivity and pollen viability was studied in two gynodioecious protandrous species of Lamiaceae, in addition to measuring some floral morphological characters over the life span of the flowers. KEY RESULTS: Three plant types in each species were found: plants bearing hermaphrodite (or male fertile) flowers (MF), female (or male sterile) flowers (MS) and intermediate flowers (INT). Plant types differed in flower size, with MS types being shorter than the other two types. There was no difference in style length among plant types in T. capitatum. Stigma receptivity decayed with floral age and was negative and significantly correlated with pollen viability in the two species, and positive and significantly correlated with style length in O. syriacum but only in MS flowers of T. capitatum. CONCLUSIONS: Reduction in size of floral characters is associated with male sterility, except style length in T. capitatum. MF flowers have two successive reproductive impediments: self-pollination and pollen-stigma interference. In both species, self-pollination is avoided by dichogamy (negative correlation between stigma receptivity and pollen viability), and pollen-stigma interference shows two different patterns: (1) style elongation in O. syriacum is characterized by a significant length increase, final MF dimensions are greater than those of MS dimensions, and style length is positively and significantly correlated with stigma receptivity; and (2) style movement in T. capitatum is characterized by a non-significant increase in style length, final MF floral dimensions are similar to those of MS dimensions, and there is no correlation between style length and stigma receptivity.     

Discovery of Bisexual Flowers in Pterocarya Stenoptera C. DC.

This paper reports the bisexual structure of the flowers of Pterocarya stenoptera. The bisexual flowers are borne at the end of a leafy shoot of the current year in many-flowered terminal pendulous catkins. They have the same structure as the general female ones. Each flower grows in the axil of a bract, with a pair of bracteoles and four small perianths. Each flower has two or three carpels in the centre of the flower, and upon them there are two or three styles with stigmas on the inner face. They differ from the general female ones in that each of them contains 4-6 stamens, forming a single whorl. The stamens alternates with, or is opposite to, the perianth elements. Sometimes they contain 8 (-10) stamens, forming two whorls, with 6 in the outer whorl and 2 (-4) in the inner whorl, and in this case the pistil in the bisexual flower of terminal catkins often becomes a rudiment. It is interesting that we have also found bisexual flowers in another tree, which are borne in lateral male catkins. They have the same structure as general male ones, and the pistils are often represented by a rudiment. Manning (1940) points out that some female flowers of Pterocarya stenoptera and P. fraxinifolia occasionally have stamens ( ? ) opposite the sepals. In P. stenoptera we have found that both the stamens and the stigmas of bisexual flowers are functional. They are capable of producing functional fruits. This is the same case as in Myrica Gale described by Davey and Gibson (1917). Rendle (1952) points out that in the male flowers of Platycarya the pistils often appeared as a rudiment. He considers, however, the male flowers derived from the bisexual flowers with an indefinite number of stamens. The rudimentary pistils of lateral male catkins in P. stenoptera we found are just the same as the ones found in Platycarya by Rendle. The discovery of the bisexual flowers in P. stenoptera may prove that the unisexual flowers of the present-day Juglandaceae are derived from ancestors with bisexual flowers.This tends to support the hypothesis that Cycadicae is the possible ancestor of the angiosperms.     

Inflorescence structure and generic delimitation of Triplaris and Ruprechtia (Polygonaceae)

A revision of the generic limits between Triplaris and Ruprechtia (Polygonaceae), which were confused in earlier literature, led to the conclusion that the two genera should be maintained. Triplaris is characterized by 1–flowered pistillate partial inflorescences, absence of a basal pedicel–like extension of the fruiting perianth–tube, which is always as long as or longer than the achene, bracteoles completely fissured on the abaxial side, and sessile or subsessile male flowers with perianth segments always connate for more than half of their length.
Ruprechtia has 2–3–flowered monochasial pistillate part–inflorescences (except the 1–flowered R. triflora) , a basal pedicel–like extension of the fruiting perianth–tube, which is at most 3/4 as long as the achene, more or less tubular bracteoles only exceptionally fissured down on the abaxial side, and pedicellate male flowers with perianth segments never connate for more than one third of their lenght. Preliminary paly–nological studies have shown that the pollen of Triplaris are microreticulate or punc–tate–microreticulate while Ruprechtia pollen have perforate–rugulose surfaces.     

Floral morphology and anatomy of Pittosporum tobira (Pittosporaceae)

Comparative studies are made on floral morphology and anatomy of female and male flowers of Pittosporum tobira. The two types of flower differ little from each other in structure at the early stage of floral development, but appear dimorphic towards anthesis. The male flower becomes cryptically bisexual, although its pistil is slender compared to that of the female flower. The stigmas of the male flower are receptive and can induce pollen germination. The structure of the style in the male flower is identical to that in the female flower. Ovules are produced on the protruded parietal placenta in the male flower, but their development is arrested at the stage of the 4–nucleate embryo sac. The female flower is clearly unisexual, with obviously aborted and sagittate anthers. Its pistil is rather plump and can produce darkish red seeds immersed in sticky pulp. The male and female flowers are similar in vascular anatomy. A conspicuous difference between the two types of flower lies in the stamens. Variation of sexual organs in the genus Pittosporum is reviewed. We assume that the flowers of Pittosporum are derived from the hermaphrodite-flowered ancestor and the female flower has become unisexual through partial reduction of sexual organs at a faster rate than the male flower.     

BREEDING SYSTEM IN FICUS CARICA,THE COMMON FIG. I. FLORAL DIVERSITY

Coevolution in Ficus carica (Moraceae) and the fig wasp (Blastophaga psenes, Agaonidae, Chalcidoidea) has resulted in a complex breeding system involving two tree morphs (Caprifig and Edible fig), three floral forms (long-styled female, short-styled female, and male flowers) and the insect pollinator. The two female floral forms have been reported to differ only in style length and stigma shape. In the present study, we demonstrate that the two female flowers differ from inception—short-styled flower primordia are smaller and exhibit significantly greater individual variation than do those of the long-styled flower, and the relative growth rate of each flower type differs. Mature forms exhibit disparity in style length, in stigma characteristics, and in degree of fusion of stylar lobes. Female flowers of both tree morphs are unisexual from inception. Male flowers of the Caprifig tree morph are initiated as hermaphrodites and gynoecium abortion occurs before megaspore mother cell stage. A single inflorescence therefore expresses two pathways to unisexuality. Hermaphrodite flower primordia were repeatedly found in the supposedly unisexual female syconium of the Edible fig tree morph. Based on its developmental morphology, Ficus carica appears to be of gynomonoecious ancestry.     

Polyspora huongiana sp. nov. (Theaceae) from Vietnam and notes on related species

A new species of Polyspora Sweet (Theaceae) endemic to the Bidoup‐Nui Ba National Park, Lam Dong Province, Vietnam, is described and illustrated: Polyspora huongiana Orel, Curry & Luu. The newly described species has variably shaped, coriaceous, narrowly elliptical leaves, terminal, pedicellate, mostly solitary, rather fleshy, dark pink to red flowers, with petals in two whorls; a columnar, seamlessly fused style with 3–5 apical lobes; persistent bracteoles; and a superior 3–4 (–5) chambered ovary. The morphological evidence supports taxonomic placement in the genus Polyspora. A new name is provided and new combinations are made for some other species in the region.     

Floral development in Aphandra (Arecaceae)

The organogenesis of staminate flower clusters and flowers and some observations on the corresponding pistillate structures of Aphandra natalia are described and compared with those of the other two genera in the Phytelephantoideae (Arecaceae). In Aphandra, staminate flowers are borne in monopodial clusters of mostly four (1-6) flowers. Each flower is surrounded by two pairs of subopposite bracteoles and has two rather indistinctly four-parted whorls of perianth parts. Stamen primordia arise on a shallow apical dome and then centrifugally down the sides of a long, angled, and laterally flattened receptacle. Immediately before the staminate bud opens, the floral receptacle below the androecium rapidly elongates, becoming funnel-shaped, with the bracteoles and a perianth sheath adnate to it forming a pseudopedicel. Epidermal and subepidermal layers of these pseudopedicels split at anthesis and release a great number of raphide idioblasts that resemble the pollen grains in shape and size. It is hypothesized that the idioblasts deter pollen feeding or ovidepositing insects. The phylogenetic implications of these findings are important within the Phytelephantoideae and among palms in general.     

Comparative floral development in male and female plants of Palmer amaranth (Amaranthus palmeri)

Premise

Characterizing the developmental processes in the transition from hermaphroditism to unisexuality is crucial for understanding floral evolution. Amaranthus palmeri, one of the most devastating weeds in the United States, is an emerging model system for studying a dioecious breeding system and understanding the biological traits of this invasive weed. The objectives of this study were to characterize phases of flower development in A. palmeri and compare organogenesis of flower development in female and male plants.

Methods

Flower buds from male and female plants were dissected for light microscopy. Segments of male and female inflorescences at different stages of development were cut longitudinally and visualized using scanning electron microscopy.

Results

Pistillate flowers have two to three styles, one ovary with one ovule, and five obtuse tepals. Staminate flowers have five stamens with five acute tepals. Floral development was classified into 10 stages. The distinction between the two flower types became apparent at stage four by the formation of stamen primordia in staminate flowers, which developed female and male reproductive organs initially, as contrasted to pistillate flowers, which produced carpel primordia only. In staminate flowers, the putative carpel primordia changed little in size and remained undeveloped.

Conclusions

Timing of inappropriate organ termination varies across the two sexes in A. palmeri. Our study suggests that the evolution of A. palmeri from a cosexual ancestral state to complete dioecy is still in progress since males exhibited transient hermaphroditism and females produced strictly pistillate flowers.     

Floral development in the legume tree Colophospermum mopane, Caesalpinioideae: Detarieae

Floral ontogeny of Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Leonard, an apetalous member of the Crudia group with four sepals and a large number (20–25) of stamens, was studied as part of a larger project on reproductive biology of this much-utilized tree. The flowers have been described as being inserted in the axil of a bract, but lacking lateral bracteoles. Four outer, light cream or white 'sepals' are present. The first two sepals are initiated in a lateral position, where the bracteoles, if present, develop in other members of the Caesalpinioideae. The inner sepals arise simultaneously adaxially and abaxially. These four structures, conventionally regarded as sepals, enclose the bud. The outer two 'sepals' should be regarded as lateral bracteoles inserted at the apex of the pedicel. The inner structures represent the only two sepals. The large number of stamens arise on a large meristematic surface and different whorls were not observed. The filaments elongate within the bud and after anthesis become exposed outside the flowers. The filaments are of equal length and the large anthers form a suspended cluster. One carpel develops terminally and gives rise to an indehiscent one-seeded fruit.     

Floral sex ratios and gynomonoecy in Aster (Asteraceae)

Gynomonoecy is the sexual system in which female and bisexual flowers occur on the same plant. This system has received little attention despite the considerable work on other plant sexual systems in the past few decades. Our study examines one hypothesized advantage of having two flower types on a plant, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined 16 species of Aster (Asteraceae), a genus of gynomonoecious, perennial herbs. Plants in this genus produce heads consisting of a whorl of female flowers around a cluster of bisexual flowers. Among field-grown plants we found no evidence that plant size, date, position of heads, rainfall, or shade influenced the proportion of female flowers. A series of greenhouse experiments likewise revealed no large or consistent effects of light, nutrients, or position of heads on the proportion of ray flowers. While floral ratios proved very stable in the face of environmental and physiological variables, they exhibited significant variation among plants and among sibships in most species. We conclude that the presence of two flower types in gynomonoecious asters is not advantageous in permitting flexibility in allocation of resources to male and female functions. We believe that the advantage of the female flowers in aster heads lies either in reducing pollen-pistil interference or in attracting pollinators.     

Aspalathus abbottii (Fabaceae: Crotalarieae), a new species from KwaZulu-Natal, South Africa

A new species Aspalathus abbottii C.H. Stirt. & Muasya, is described. The species is known only from Oribi Flats, KwaZulu-Natal, where it grows in grassland vegetation. The new species is characterised by its rigid spreading habit, densely and shortly villous branches, glabrous bracts and bracteoles, and 1(2) bright yellow flowers borne on short lateral shoots. It is most similar to other grassland species, A. frankenioides DC. and A. gerrardii H. Bol., all from the summer rainfall area of South Africa but differs in its rigid spreading habit, few bright yellow flowers per flowering branchlet, glabrous bracts and bracteoles, villous yellowish-green seasonal shoots, and its pale brown to tan over-seasonal branches with a blackish lattice of peeled bark.     

水烛的花部形态观察——兼论与长苞香蒲的分类学界定

通过腊叶标本研究、野外观察和文献考证,结合栽培试验,研究了香蒲科水烛（Typha angustifolia L.）花部结构特征,补充描述了该种丝状毛在子房柄上的着生方式、小穗不孕雌花数目等性状特征,观察了在成熟期不同阶段其孕性雌花柱头与小苞片的长度变异。结果显示,水烛孕性雌花小苞片呈宽披针形、匙形或条形,先端褐色,短于柱头,或与柱头近等长或稍长于柱头;子房柄上的丝状毛除少数散生外,多数基部合生呈鞘状或束状,在子房柄下部呈1～4轮排列;小穗不孕雌花常3（～4）枚。研究材料在7月中旬前后雌花小苞片明显短于柱头,随果穗成熟小苞片与柱头近等长。长苞香蒲（T.domingensis Pers.）子房柄上的丝状毛形态和着生方式与水烛中的情况基本一致,但小苞片白色透明,小穗不孕雌花常1（～2）枚。这表明水烛孕性雌花小苞片和柱头的长度比例与不同成熟阶段有关系,不宜作为与长苞香蒲的区别特征,而小穗不孕雌花数目和小苞片颜色等特征对两物种的划分有较重要的意义。