FLORAL DEVELOPMENT IN MYRISTICA (MYRISTICACEAE)

Myristica fragrans and M. malabarica are dioecious. Both staminate and pistillate plants produce axillary flowering structures. Each pistillate flower is solitary, borne terminally on a short, second-order shoot that bears a pair of ephemeral bracts. Each staminate inflorescence similarly produces a terminal flower and, usually, a third-order, racemose axis in the axil of each pair of bracts. Each flower on these indeterminate axes is in the axil of a bract. On the abaxial side immediately below the perianth, each flower has a bracteole, which is produced by the floral apex. Three tepal primordia are initiated on the margins of the floral apex in an acyclic pattern. Subsequent intercalary growth produces a perianth tube. Alternate with the tepals, three anther primordia arise on the margins of a broadened floral apex in an acyclic or helical pattern. Usually two more anther primordia arise adjacent to each of the first three primordia, producing a total of nine primordia. At this stage the floral apex begins to lose its meristematic appearance, but the residuum persists. Intercalary growth below the floral apex produces a columnar receptacle. The anther primordia remain adnate to the receptacle and grow longitudinally as the receptacle elongates. Each primordium develops into an anther with two pairs of septate, elongate microsporangia. In pistillate flowers, a carpel primordium encircles the floral apex eventually producing an ascidiate carpel with a cleft on the oblique apex and upper adaxial wall. The floral ontogeny supports the morphological interpretation of myristicaceous flowers as trimerous with either four-sporangiate anthers or monocarpellate pistils.     

Ontogeny of Staminate and Carpellate Flowers of Schisandra sphenanthera(Schisandraceae)

The ontogenetic process of the staminate and carpellate flowers of Schisandra sphenanthera Rehd. et Wils., an endemic species to China, was observed for the first time under the scanning electron microscope (SEM). In the staminate flowers, the perianth units and stamens were initiated acropetally in a continuous fasion with 2/5 spiral phyllotaxis, while no female structures were formed. Anthers were differentiated prior to the filaments formation. Throughout all the stages were the stamens arranged spirally on a columniform receptacle. In the carpellate flowers, the initiation sequence of the perianth units and carpels were similar to that of the staminate flowers. In contrast, no male structures were formed. Shortly after initiation, the carpel primordia began their marginal growth besides the apical growth and then appresses were formed on the adaxial surfaces of the primordia. However the lower margins of these appresses were inconspicuous, resulting in conduplicate carpels. Two ovules were developed on the inner surface near either lateral margins of the carpel, shaping laminar placentae. Compared with S. glabra (Brickell) Rehd., a related American species, the evolutionary trend of phyllotaxis of androecia is considered that stamens may change from spiral to approximately whorled arrangement, accompanying with the change of receptacle from a column to a flattened shield. It was also suggested that the stamens being numerous and uncertain in number become certain and decrease in number to 5 (4－7). Sterile stamens are observed and the unisexual nature of the flowers is discussed. Two types of carpel primordia are categorized, corresponding to two types of carpels, namely, ascidiate and conduplicate carpels, respectively.     

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.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE. XI. THE FLORAL BIOLOGY OF NELUMBO PENTAPETALA

The floral biology of Nelumbo pentapetala (Walter) Fernald, the American lotus, native to Texas, was investigated. Anthesis occurs over three consecutive days with flowers opening each morning and closing around noon. First-day flowers are protogynous with the perianth parts partially expanded so that pollen-covered insects which are attracted by floral color and the intense “fruity” odor (diffused with the aid of increased floral temperature) are directed on to the flattened receptacle (= carpellary receptacle) from which the receptive stigmas protrude, thus accomplishing pollination. During the second morning anther dehiscence begins and insects which visit and forage within the flower become covered with pollen and typically crawl over the still receptive stigmas achieving “facilitated” self-pollination (indirect autogamy). By mid-morning of the second day the stigmas dry and become non-receptive to pollen. During the third day of anthesis perianth and staminal parts quickly abscise and over the period of a few weeks the receptacle and enclosed fruits mature. In most populations studied, Hymenoptera (e.g., Lusioglossum spp., and Apis mellifera) were the most abundant and effective pollinators. In some populations, however, Coleoptera (e.g., Chauliognathus) were also numerous and effective pollinators. It is suggested that the overall floral structure (e.g., large numbers of stamens, masses of pollen, staminal appendages) are adaptations which facilitate the pollination of Nelumbo by beetles.     

倒地铃花的形态分化与花药结构研究

利用体视显微镜、半薄切片和超薄切片法对倒地铃(Cardiospermum halicacabum Linn.)雄花和假两性花开花过程及花药发育过程进行了观察和比较研究。结果显示:(1)花蕾发育早期,倒地铃雄花和假两性花的花蕾形态没有区别;花蕾发育后期,雄花雌蕊退化,假两性花雌蕊继续发育,花蕾外部形态出现差异;开花时雄花花药开裂,假两性花花药不开裂。(2)倒地铃雄花和假两性花均具四室花药,呈蝶形;花药壁细胞从外到内依次是表皮、药室内壁、中层(2层)和绒毡层;花药壁发育为基本型,绒毡层为单核分泌型,四分体为四面体型,花粉粒两核;开花时雄花和假两性花中层都有残留;小孢子液泡化时,绒毡层开始降解,两核花粉粒时,假两性花绒毡层降解较快。(3)雄花药室内壁次生加厚完全,裂口区发育,连接同侧花粉囊的连接组织降解,花药开裂;假两性花药室内壁次生加厚不完全,具唇形细胞,药隔细胞壁未降解,同侧花粉囊未连通,花药四室,不开裂;假两性花成熟花粉粒细胞质稀少,内壁不完整。本研究结果表明,倒地铃的雄花是由两性花在发育早期雌蕊停止发育形成的,假两性花则由两性花在发育晚期雄蕊功能退化造成的。     

Development and morphology of flowers and inflorescences in Balanophora papuana and B. elongata (Balanophoraceae)

Extreme modification and reduction in floral morphology presents an obstacle to determining the evolutionary relationships and homologies of the holoparasites in Balanophoraceae. Developing flowers and inflorescences of two dioecious species, Balanophora papuana and B. elongata, were compared to each other and to the monoecious B. fungosa. Intermingled with flowers in the male inflorescences are bracts (B. elongata) or bract parts (B. papuana). In the latter, early cessation of bract tip growth results in two half-bracts, which become displaced during inflorescence elongation, thus disproving the view that these bract-like structures are axial in nature. Male flower primordia emerge in positions axillary to the dividing bracts, and both arise in a spiral sequence. This pattern is modified in B. papuana by the formation of pseudowhorls of four. In both species, the staminate flowers consist of a generally four-merous perianth and a synandrium of congenitally fused stamens. Male flower and bract ontogeny (but not pollen sacs) conform to patterns seen in other angiosperms. More problematic are the carpellate flowers whose primordia arise in irregular order between club-shaped, radially symmetrical organs called claviform bodies. The interpretation that these bodies are homologous to the peltate bracts of Helosideae appears plausible, but cannot explain their nonspiral initiation and radial symmetry.     

Thrips pollination of the dioecious ant plant Macaranga hullettii (Euphorbiaceae) in Southeast Asia

Discussion about thrips (Thysanoptera) as main pollinators has been controversial in the past because thrips do not fit the preconception of an effective pollinator. In this study, we present evidence for thrips pollination in the dioecious pioneer tree genus Macaranga (Euphorbiaceae). Macaranga hullettii is pollinated predominantly by one thrips species, Neoheegeria sp. (Phlaeothripidae, Thysanoptera). As a reward for pollinators, the protective floral bracteoles function as breeding sites for thrips and trichomal nectaries on the adaxial surface of the floral bracteoles provide alimentation. Flowering phenology of both staminate and pistillate trees was highly synchronized within 3-4 wk periods. In contrast to pistillate trees, staminate trees start to breed the thrips inside the developing inflorescences ～2 wk before anthesis. Breeding of Neoheegeria sp. in the laboratory indicates that the thrips development is completed within ～17 d. Thus, staminate trees offer breeding sites for one thrips generation until the onset of pollen presentation. Intraspecific pollen transfer by thrips was proved by pollen loads of thrips taken from receptive pistillate inflorescences of M. hullettii. Bagging experiments of different mesh sizes showed that seed set reached almost the level of open-pollinated flowers when exclusively tiny insects like thrips were able to enter the net bags, but no apomictic seed set occurred when no insect access was given to the flowers.     

The role of staminate flowers in the breeding system of Olea europaea (Oleaceae): an andromonoecious, wind-pollinated taxon

BACKGROUND AND AIMS: Andromonoecy, as a breeding system, has generated a considerable body of theory in terms of sexual selection, but extended records comparing the performance of pollen grains from staminate versus hermaphrodite flowers are still sparse. The objective in this study was to elucidate the role of staminate flowers in the andromonoecious breeding system of olive (Olea europaea). METHODS: To determine the meaning of staminate flowers, an evaluation was made of resource allocation to, and phenology of, staminate and hermaphrodite flowers in the cultivar 'Mission', and a comparison was made of the male function between both kinds of flowers. KEY RESULTS: Dry weight of hermaphrodite flowers was 19 % greater than dry weight of staminate flowers arising in comparable positions of the panicle. This difference was mainly due to pistil and petal weight; there were no significant differences in stamen weight. There were no significant differences between staminate and hermaphrodite flowers in either amount of pollen per anther, or pollen quality as determined by pollen viability, germinability or ability to fertilize other flowers. There was no significant link between gender and time of anthesis. However, position of the flower within the panicle correlated with time of anthesis and gender. Flowers at the apex and at primary pedicels tended to be hermaphrodite and open earlier, whereas flowers arising in secondary pedicels were mainly staminate and were commonly the last to reach anthesis. CONCLUSIONS: It is proposed that the main advantage provided by production of staminate flowers in olive is to enhance male fitness by increasing pollen output at the whole plant level, although a relict function of attracting pollinators cannot be completely discarded.     

Flower Structure and Reproductive Biology of Bougainvillea stipitata (Nyctaginaceae)

Abstract: Bougainvillea stipitata displays inflorescences with three pendant greenish flowers. Flowers open at sunset and last five days. Flower perianth is constricted in the middle and forms a tube that ends in five lobes. Fragrance is emitted by the papillae located on the lobe margins of the perianth. The nectary is located at the base of the staminal tube. It secretes fructose-dominant nectar with amino acids, phenols and reduced acids. Nectar secretion is continuous during flower lifetime and the flowers do not recover the reward. Mainly moths visit flowers. Pollen load on stigmas indicates that most flowers received more than 50 pollen grains, which are deposited by pollinators within the first two days of the flower life. Although the low natural fruit set of this self-incompatible species may be due to intraplant pollen flow, pollinators play an essential role for B. stipitata fruit production.     

The pollination of Trimenia moorei (Trimeniaceae): floral volatiles,insect/wind pollen vectors and stigmatic self-incompatibility in a basal angiosperm

Trimenia moorei (Oliv.) Philipson is an andromonoecious liane with >0.40 of the total flower buds maturing as bisexual flowers. Male and bisexual flowers are strongly scented with pollen, anther sacs and receptacle scars testing positively for volatile emissions. Scent analyses detect over 20 components. The major fatty acid derivative is 8-heptadecene, and 2-phenylethanol dominates the benzenoids. While hover-flies in the genera Melangyna and Triglyphus contact the stigma with their probosces, the stigma secretes no free-flowing, edible fluids. Copious pollen is the only edible reward consumed by hover-flies (Syprhidae), sawflies (Pergidae) and bees in the families Apidae, Colletidae and Halictidae. All these insects carried pollen of T. moorei on their heads, legs and thoraces and female bees in the genera Apis, Exoneura, Leioproctus and Lasioglossum stored pollen on their hind legs. Pollen traps also indicate that pollen is shed directly into the air, permitting wind pollination. When bisexual flower buds are bagged (isolated from insect foragers) on the liane then subjected to a series of hand-pollination experiments after perianth segments open, the structural analyses of pollen-carpel interactions indicate that T. moorei has a trichome-rich dry-type stigma with an early-acting self-incompatibility (SI) system. Bicellular pollen grains deposited on stigmas belonging to the same plant germinate but fail to penetrate intercellular spaces, while grains deposited following cross-pollination reach the ovule within 24 h. Fluorescence analyses of 76 carpels collected at random from unbagged (open-pollinated) flowers on five plants indicates that at least 64% of carpels are cross-pollinated in situ. Trimenia moorei is the first species within the ANITA group, and second within reilictual-basal angiosperm lineages, to exhibit stigmatic SI in combination with dry-type stigma and bicellular pollen, a condition once considered to be atypical for angiosperms as a whole but now known to be present in numerous taxa.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: A CATKIN WITH JUGLANDACEOUS AFFINITIES

Three specimens of one type of fossil catkin from the Middle Eocene of Tennessee are excellently preserved and have been investigated morphologically. The flowers on these catkins are subtended by elongate, three-lobed bracts, are exclusively staminate, and have three conspicuous, obovate, perianth parts that bear large peltate scales. The stamens are well preserved and contain triporate pollen grains that are equivalent to the dispersed pollen genus Momipites. Floral morphology, cuticular features, and pollen indicate close affinities with the extant genera Engelhardia, Oreomunnea, and Alfaroa of the Juglandaceae; but because the fossil catkins are distinct and are a dispersed plant organ, they are placed in a new form genus: Eokachyra. These fossil flowers represent a rare opportunity to correlate the micro- and macrofossil record and to compare the relative rates of evolution of these features. The fossil catkins also demonstrate that much structural information may be gained from the study of fossil angiosperm flowers. The similarities between the staminate flowers of the fossil catkins and the staminate flowers of Engelhardia, Oreomunnea, and Alfaroa confirm the idea that this complex has had a long evolutionary history and suggest that the pollination system of certain extant genera was well developed during Middle Eocene times.     

Beautiful,complicated—and intelligent? Novel aspects of the thigmonastic stamen movement in Loasaceae

In a recent study we investigated the complex mechanisms regulating the pollen release via thigmonastic stamen movement found exclusively in Loasaceae subfamily Loasoideae. We demonstrated that stamen movement is modulated by abiotic (light and temperature) as well as biotic stimuli (pollinator availability and visitation frequency). This is explained as a mechanism to adjust the rate of stamen movement and thus pollen dispensation to different environmental conditions in order to optimize pollen transfer. Stamen movement is rapid and thus a near-immediate response to pollinator visits. However, Loasaceae flowers also show a response to biotic stimuli on a longer time scale, by adjusting the duration of both the staminate and the carpellate phase of the anthesis. We here present two additional data sets on species not previously studied, underscoring the shortening of the staminate phase in the presence of pollinator visits vs. their absence and the shortening of the carpellate phase after pollination. Overall, the plant shows not only a rapid but an “intelligent” reaction to its environment in adjusting anthesis and pollen presentation to a range of factors. The physiological and morphological bases of the stamen movement are poorly understood. Our previous study showed that there is no direct spatial relationship between the place of stimulation in the flower and the stamen bundle activated. We here further show the morphological basis for stamen movement from a reflexed into an erect position: Only the basal part of the filament curves around the receptacle, while the upper part of the filament retains its shape. We hypothesize that the stimulus is transmitted over the entire receptacle and the place of reaction is determined by stamen maturity, not the location of the stimulus.     

FUNCTIONAL DIOECY AND ANDROMONOECY IN SOLANUM

Field and laboratory studies of 19 diclinous species endemic to Australia help to clarify the nature and evolution of andromonoecy, androdioecy, and dioecy in the genus Solanum. Ten species are andromonoecious; typically these species bear inflorescences with a single, large basal hermaphroditic flower and 12–60 distal, smaller staminate flowers. We suggest that the andromonoecious condition was derived from hermaphroditic-flowered ancestors in part by hemisterilization of flowers but largely by addition of staminate flowers. The resultant larger inflorescences are hypothesized to serve both to attract and to entrain pollinators, yielding more or higher-quality seed set in hermaphroditic flowers and/or greater dispersion of pollen from staminate flowers. We suggest that andromonoecy may also serve to reduce selling. Nine other species are morphologically androdioecious but functionally dioecious. In these species, staminate flowers, like those of the andromonoecious species, bear anthers with copious tricolporate pollen and a highly reduced gynoecium. The morphologically hermaphroditic flowers are functionally pistillate and borne singly in inflorescences, and they bear anthers with inaperturate pollen. The inaperturate pollen, although viable, never germinates and is hypothesized to be retained in pistillate flowers as a reward to pollinators in the nectarless Solanum flowers. All other species of Solanum studied with pollen dimorphism in which one pollen morph is inaperturate are also best treated as functionally dioecious. We conclude that there is no evidence for androdioecy in Solanum. A review of other families suggests that there is little support for this unusual breeding system in any other angiosperm group either. Preliminary analyses suggest that andromonoecy and dioecy are polyphyletic in Solanum. Furthermore, dioecy is as likely to have arisen from hermaphroditic as from andromonoecious ancestors.     

DEVELOPMENTAL STUDIES IN PTYCHOSPERMA (PALMAE). I. THE INFLORESCENCE AND THE FLOWER CLUSTER

This paper describes inflorescence structure, including organogenesis of the panicle and flower clusters and vasculature of flowering branches, for two species of Ptychosperma, a genus of arecoid palms. The inflorescence is an infrafoliar panicle with up to four orders of branches in a spirodistichous arrangement conforming to an irregular one-half phyllotaxy. The primordium of the inflorescence is crescentic and the apex has two tunica layers, a group of central cells, and a rib meristem. The distal flower-bearing parts or rachillae of all branches develop acropetally early in ontogeny and are vertically oriented in the bud. Although these rachillae terminate branches of different sizes and orders, they are similar in size and in number of flower clusters produced. Internodes and lower parts of branches develop later. Bracts of four types are produced: a prophyll and empty peduncular bract, bracts which subtend lateral branches, bracts subtending triads, and floral bracteoles. The prophyll and peduncular bracts are tubular and completely closed around all branches until about three months before the flowers reach anthesis. Bracts subtending lateral branches and those that subtend triads enlarge by small amounts of apical, adaxial, and marginal growth to cover subtended apices during early ontogeny, but are small to absent at maturity. Flower clusters are triads of two lateral staminate and a central pistillate flower. Organogenesis indicates that the triad is a sympodial unit. Flowers develop successively, each floral apex bearing a bracteole that subtends the next flower. The vasculature of the inflorescence may be divided into two systems. Bundles of the main axis extend acropetally into the vertically oriented branches as they are initiated and form a central cylinder of larger bundles in each branch. Flower clusters are supplied by a peripheral system of smaller bundles that develop later in relation to the developing floral organs. Bundles of the peripheral system branch frequently, but branching levels are irregular. The irregular branching of peripheral bundles appears related to the phyllotaxy of the flower clusters and the random right or left position of the first flower of the triad. The level of branching of a bundle may depend on the position of a floral primordium with respect to an existing procambial strand. Three (-4) bundles supply each staminate flower and six (-10) the pistillate flower. The histologically specialized inflorescence has stomata and contains abundant starch. Tannins and raphides, spherical silica bodies, and various forms of sclerenchyma appear in sequence and apparently provide support and protection during the long exposure of the branches.     

Organogenesis of Staminate Flowers in the Genus Schisandra and Its Systematic Significance

The great morphological variation in staminate flowers makes it favorable for its use as the main criteria for infrageneric classification in the genus Schisandra (Schizandra) Michx. Organogenesis of different kinds of the staminate flowers has been observed under SEM. Combined with other currently available studies, the patterns of morphogenesis of the staminate flowers are categorized into three types: the columnar-torus type, the flattened-torus type, and the spherical-torus type. In the columnar-torus type, the torus of the staminate flower is kept columelliform through out the whole ontogenic process of the flower; this type can be further divided into two subtypes—the sphenantheraceous subtype, with the thecae laterally localized on both sides of the connective of the mature stamen, and the grandifloraceous subtype, instead with the thecae located outward or slightly outward. In the flattened-torus type, the torus of the staminate flower gradually becomes swollen and then flattened in the process of floral development, and forms a pentagonal shield together with the enlarged filaments and connectives of the stamen. The torus of the staminate flower in the spherical-torus type becomes carnified and swollen with the stamen growing into the depressions or cavities of the spherical torus. Among the three types, the columnar-torus one might be the primitive type, from which the other two were derived representing two different evolutionary trends respectively. By analyzing the cause of the morphological variation of the staminate flowers, it is suggested that the evolutionary pressure by the insect eating during pollinating enhanced the drastic differentiation of the morphology of the staminate flowers. In some taxa of the genus, in which the Coleoptera acted as the main pollinating agent, the enlargement of the torus of the staminate flower to form a thick flattened shield or a spheroid might be an adaptive fitness to the phylogenetic decreasing in number of the stamen. The primitiveness in stamen morphology of the Schisandra staminate flowers is also discussed, which might agree with the origin antiquity of the genus. The similarity of its heteropolar 3- or 6-aperturate pollen to the 3-aperturate pollen of Eudicots might result from convergent evolution. In addition, main infrageneric classifications of Schisandra and the systematic p     

Intra-individual heterostyly in Atriplex halimus L. (Amaranthaceae)

Classically, the Atriplex halimus L. female flower is perianthless, has two bracteoles, one ovary and one style. Considering bracteoles, one can distinguish, among the representatives of two Tunisian populations, three phenotypes of female flowers, each of them being distributed in three types according to the style length. Male flowers produce three types of pollen. This is the only known example of intra-individual heterostyly in unisexual flowers. These results question the classical concept of individual. The authors discuss a possible process implying indirectly hybridisation and introgression between A. halimus and A. nummularia.     

花叶芋(天南星科)的花器官发生

利用扫描电镜首次观察了天南星科花叶芋(Colocasia bicolor) 的花器官发生过程。花叶芋的肉穗花序由无花被的单性花构成, 雌花发生于花序基部, 雄花发生于花序上部, 中性花位于花序中间部位。雄花: 3 或4 个初生雄蕊原基轮状发生, 随后每个初生原基一分为二, 形成6或8个次生原基; 一部分次生原基在其后的发育过程中融合, 形成5 或7 枚雄蕊; 雄花发育过程中未见雌性结构的分化; 花药的分化先于花丝; 雄蕊合生成雄蕊柱。雌花: 合生心皮, 3或4个心皮原基轮状发生, 未见雄性结构的分化。中性花来源于雌雄花序过渡带上, 属于雄蕊原基的滞后发育以及发育成熟过程中的退化; 与彩叶芋属(Caladium)不同, 此过渡区未见畸形两性花。初生雄蕊原基二裂产生次生原基的次生现象在目前天南星科花器官发生中显得比较特殊, 同时初步探讨了次生原基的融合方式。     

Histological and Morphological Studies of Pollen Grains from Elongata, Reduced Elongata and Staminate Flowers in Carica papaya L.

The quality and quantity of pollen from three types of flowers; elongata, reduced elongata and staminate from the commercialized Thai papaya cultivar ‘Khak Nual’ were determined using pollen morphology, pollen physical characters and pollen development processes. Pollen development progressed at the same pace in the three types of pollen-producing flowers and was consistent with pollen development in many angiosperms. Pollen morphology showed that papaya pollen grains are tricolporate, with three apertures, and there is no significant difference in diameter (25.18–25.72 μm) and weight (11.76–15.45 ng) among pollen sources. The staminate flower shows the lowest amount of pollen, with 12,368 pollen per anther, but higher viability and germination rates of 95.53 % and 53.64 %, respectively. In contrast, the elongata type shows the highest amount of pollen grains with 14,884 pollen per anther and the lowest viability and germination rates, 93.06 % and 46.33 % respectively. The physical characteristics of pollen grains from reduced elongate and elongate flowers are similar. Reduced elongate flower type can donate pollen without self-pollinating.     

Subdioecy in Consolea spinosissima (Cactaceae): breeding system and embryological studies

The breeding system and the embryology of Consolea spinosissima, a tree-like opuntioid endemic to Jamaica, were investigated. Morphological and embryological studies revealed that the species is subdioecious, with three sexual morphs present in the 150 × 120 m plot studied at Hellshire Hills, Jamaica. The female morph has pistillate flowers with open stigma lobes, no pollen grains, and sets fruit. The male morph has cryptic staminate flowers with closed stigma lobes, viable pollen grains, and a nonfunctional gynoecium that does not set seed. The weak hermaphrodite morph has low fruit set and "perfect" flowers that superficially resemble the functionally staminate flowers of the male morph. These perfect flowers reach anthesis with viable pollen grains, with no or only a few functional ovules, and with the style supporting pollen tube growth. Embryological studies showed that the critical stage for sex determination occurs earlier in pistillate than in staminate and perfect flowers. Anthers of pistillate flowers abort prior to microspore tetrad formation, whereas ovules of the staminate and perfect flowers degenerate after the complete maturation of the embryo sac. Based on flower structure and embryological data, we hypothesize that the ancestor of C. spinosissima is/was hermaphroditic.     

新疆郁金香一居群个体性别7年的动态变化

在雌雄同株植物中, 花性别被认为是两性资源分配对环境条件的响应, 了解个体性别随时间的变化对探讨植物性系统的变异有重要意义。早春短命植物新疆郁金香(Tulipa sinkiangensis)多为两性花居群, 前期调查显示一些居群由雄花和两性花构成。为了探讨新疆郁金香雄花的发生与变化, 我们连续7年对一个居群的花性别及其变化动态进行了跟踪。结果显示: (1)该居群主要是由一朵花植株和两朵花植株构成, 分别占居群植株总数的74.5%和23.0%。两种性别的花随机分布在不同类型的单株上, 形成了以两性花植株为主, 含有雄株、雄花与两性花同株(andromonoecy)的居群结构。(2)雄花相对较小, 子房退化, 无胚珠发育, 在植株或居群中花期较晚出现。与相同大小的两性花相比, 雄花在单花花粉量、花粉败育率、花粉粒大小及形态、雄性功能等方面没有差异。(3) 7年间, 雄花在居群中的比例经历了2011-2014年间的显著下降(23.4-3.1%)和2015-2017年间相对稳定的零星分布(1.5-1.0%)两个阶段。居群中一朵花植株数量和两朵花植株数量在年份间呈波动性变化。(4)雄花的出现可能是植株受自身资源状况及环境条件等因素的影响在花性别选择上作出的可塑性反应。