Gender variation in Actinidia deliciosa,the kiwifruit

Summary Flower and fruit characters were measured in ten female, five male and five fruiting male selections of A. deliciosa var deliciosa (A. Chev) Liang and Ferguson. Flowers from female vines had functional pistils, which contained many ovules. Stamens appeared to be fully developed but produced only empty pollen grains. Flowers from male vines had functional stamens that produced high percentages of pollen grains with stainable cytoplasmic contents. Pistils did not contain ovules and were generally small with vestigial styles. Fruiting male vines had both staminate and bisexual flowers. Staminate flowers were similar to those found on strictly male vines. Bisexual flowers produced ovules and stainable pollen. Pistils were smaller than in pistillate flowers. Although the three flower sexes differed in style length, ovary dimensions and ovules per carpel, staminate and bisexual flowers were similar in number of flowers per inflorescence, stamen filament length, pollen stainability, inflorescence rachis length and carpel number, and differed from pistillate flowers in these characters. The three flower sexes had similar sepal and petal numbers. The fruit of fruiting males were considerably smaller than those of females. Low ovule number appears to be the major factor limiting fruit size in the fruiting males studied. Prospects for developing hermaphroditic kiwifruit cultivars through breeding are discussed.     

MORPHOLOGY,VASCULAR ANATOMY AND EMBRYOLOGY OF PISTILLATE AND STAMINATE FLOWERS OF ASPARAGUS OFFICINALIS

Flowers of three pistillate (female), two heterogametic staminate (male) and two homogametic male genotypes of Asparagus officinalis L. were compared for morphology and vascular anatomy of the flower and for embryological development to the stage of mature ovules and pollen. Flowers are liliaceous, the staminate with rudimentary pistils and the pistillate with collapsed anthers. The uncomplicated vascular pattern differs between staminate and pistillate flowers only in the size and degree of maturation of bundles to stamens and carpels. Longer styles appear to be correlated with a greater extent of ovule development in ovaries of staminate flowers. Microsporogenesis in males is normal with wall development corresponding to the Monocotyledonous type. The tapetum is glandular and binucleate, cytokinesis successive, the tetrads isobilateral or occasionally decussate, and the mature pollen grain two-celled. A pair of heteromorphic, possibly sex, chromosomes was observed in heterogametic male plants. Anther development is initially the same in pistillate flowers, but the tapetum degenerates precociously followed by collapse of microspore mother cells. In pistillate flowers the ovules are hemitropous, bitegmic, and slightly crassinucellate. Megasporogenesis-megagametogenesis conforms to the Polygonum type. In staminate flowers ovule development is like that in pistillate flowers until degeneration starts in nucellar and integumentary cells at the chalazal end. Ovules in both homogametic male genotypes rarely complete meiosis, while in the heterogametic males it is normally completed with about one ovule in 20 flowers forming a mature megagametophyte. Since manipulation of sex expression in Asparagus could be important in developing inbred male and female lines for breeding purposes, those aspects of the morphological and embryological observations presented which might be useful in planning experiments to induce sex changes are discussed briefly.     

Morphological variation in the flowers of Jacaratia mexicana A. DC. (Caricaceae), a subdioecious tree

The Caricaceae is a small family of tropical trees and herbs in which most species are dioecious. In the present study, we extend our previous work on dioecy in the Caricaceae, characterising the morphological variation in sexual expression in flowers of the dioecious tree Jacaratia mexicana . We found that, in J. mexicana , female plants produce only pistillate flowers, while male plants are sexually variable and can bear three different types of flowers: staminate, pistillate and perfect. To characterise the distinct types of flowers, we measured 26 morphological variables. Our results indicate that: (i) pistillate flowers from male trees carry healthy-looking ovules and are morphologically similar, although smaller than, pistillate flowers on female plants; (ii) staminate flowers have a rudimentary, non-functional pistil and are the only flowers capable of producing nectar; and (iii) perfect flowers produce healthy-looking ovules and pollen, but have smaller ovaries than pistillate flowers and fewer anthers than staminate flowers, and do not produce nectar. The restriction of sexual variation to male trees is consistent with the evolutionary path of dioecy from hermaphrodite ancestors through the initial invasion of male-sterile plants and a subsequent gradual reduction in female fertility in cosexual individuals (gynodioecy pathway), but further work is needed to confirm this hypothesis.     

SEX EXPRESSION,BREEDING SYSTEM,AND POLLEN BIOLOGY OF RICINOCARPOS PINIFOLIUS: A CASE OF ANDRODIOECY?

A population of 54 Ricinocarpos pinifolius (Euphorbiaceae) plants contained male plants, which produced only staminate flowers, and hermaphrodites, which produced staminate and pistillate flowers. The fraction of pistillate flowers ranged continuously from 0 to 0.68. Insect pollination was effective and fruit set virtually complete except for losses to herbivores. Self pollen, outcross pollen from male plants, and outcross pollen from hermaphrodites were all equivalent in viability, germination, tube growth, ovule penetration, and fruit setting ability. Inbreeding depression was manifested as late abortion of some selfed seeds. Geitonogamous selfing is largely prevented by temporal separation of male and female functions within plants. This temporal separation, combined with population-wide synchrony of flowering, may create unusual conditions allowing male plants at low frequency to match hermaphrodites in reproductive success.     

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.     

The functional significance of a stigma color polymorphism in Acer pictum subsp. mono (Aceraceae)

Aims Exploring the characteristics and function of a flower color polymorphism contributes to our understanding of floral evolution in angiosperms. However, little information is available on stigma color polymorphisms in flowering plants despite their important functional role in plant reproduction.Methods We studied a stigma color polymorphism at the individual level in Acer pictum subsp. mono (aka A. mono) by investigating stigma-color morph proportion and comparing stigma performance and components of female fitness (pollen adhesion, pollen germination, fruit set, seed set and fruit weight) between the two morphs (red and greenish-yellow stigma) within natural populations at Dongling Mountain in the north of China. In the flowering period, we conducted hand pollination in natural populations and then made microscopic observations using the aniline blue fluorescence method.Important findings Individuals in the studied populations did not change their stigma color between years, and flowers produced by a single tree were uniform in their stigma color. This strongly suggests that stigma color variation is genetically controlled. The percentage of the red stigma flowers with germinated pollen grains was significantly higher than that of the greenish-yellow stigma flowers when hand pollination was conducted in the early flowering period, but not so in the late flowering period. There was no significant difference in the percentage of flowers with pollen adhesion to the stigma between the two morphs. Fruit set of the red morph was significantly higher than that of the greenish-yellow morph. Our findings suggest that the red morph may be more advantageous for pollen germination and fruit set than the greenish-yellow morph, which may provide a functional explanation for the high incidence of the red stigma morph in the studied populations. Alternative explanations for the stigma color polymorphism are discussed to stimulate further work.     

POLLEN REMOVAL AND POLLEN DEPOSITION AFFECT THE DURATION OF THE STAMINATE AND PISTILLATE PHASES IN CAMPANULA RAPUNCULOIDES

We examined factors affecting the duration of the staminate and pistillate phases in the protandrous flowers of Campanula rapunculoides L. (Campanulaceae). Under conditions of natural pollinator visitation, flowers experiencing low rates of pollen removal lasted significantly longer than flowers that had faster rates of pollen removal. Experimental manipulations showed that low levels of pollen removal resulted in extension of the staminate phase. Hand-pollinations in which we varied the amount and source of pollen showed that when the number of fertilized ovules within an ovary is low, senescence of the flower is delayed, resulting in extension of the pistillate phase. We also report on pollinator foraging patterns within the vertical inflorescences of C. rapunculoides and the limiting factor for seed set in this population. The results are relevent to recent suggestions that floral characters often serve to reduce interference between the sexual functions in cosexual plants.     

The breeding system of Fumana ericifolia: first evidence of autogamy in woody Cistaceae

Fumana ericifolia belongs to the family Cistaceae, in which all perennial species previously studied have been reported to be self-incompatible and xenogamous. Here we show that F. ericifolia is self-compatible and autogamous. Its flowers last only four to eight hours and produce a small amount of pollen and ovules. Self-pollination depends on changes in the relative position of the stigma and the anthers, triggered by the abscission of the petals; this in turn causes closing of the sepals, which push the anthers onto the stigma. Pollen remains highly viable and germinable, and the stigma keeps its receptivity several hours after the loss of the petals. Hand pollination treatments revealed that fruits are produced both in selfed and crossed flowers. The germination of pollen grains on the stigma, the rate of pollen tube growth along the style, and the penetration into the ovules were similar in self-and cross-pollinations; also, there were no significant differences in fruit set, seed set and weight of seeds. Thus, we report the first evidence of autogamy in a woody Cistaceae and suggest that selfing may ensure reproductive success when pollinators are limited.     

Anther structure and pollen development in Melicoccus lepidopetalus (Sapindaceae): An evolutionary approach to dioecy in the family

Anther and pollen development in staminate and pistillate flowers of dioecious Melicoccus lepidopetalus (Sapindaceae) were examined by light and electron microscopy. Young anthers are similar in both types of flowers; they consist of epidermis, endothecium, two to four middle layers and a secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents compressed epidermal cells and endothecium cells with fibrillar thickenings. A single locule is formed in the theca by dissolution of the septum and pollen grains are shed at two-celled stage. The mature anthers of pistillate flowers differ anatomically from those of staminate flowers. The epidermis is not compressed, the endothecium does not develop fibrillar thickenings, middle layers and tapetum are generally persisting, and the stomium is nonfunctional. Microspore degeneration begins after meiosis of microspore mother cells. At anthesis, uninucleate microspores and pollen grains with vegetative and generative nuclei with no cytokinesis are observed. Some pollen walls display an abnormal exine deposition, whereas others show a well formed exine, although both are devoid of intine. These results suggest that in the evolution towards unisexuality, the developmental differences of anther wall tissues and pollen grains between pistillate and staminate flowers might become more pronounced in a derived condition, such as dioecy.     

The questionable relationship of Montinia (Montiniaceae): evidence from a floral ontogenetic and anatomical study

The systematic position of Montiniaceae remains uncertain: a relationship with Cornales has been suggested on phytochemical and embryological evidence, while molecular data point to a relationship with Solanales. We investigated the floral development and anatomy of the South African Montinia caryophyllacea to add a new set of characters for clarifying the systematic position of the family Montiniaceae. Pistillate inflorescences show a higher degree of reduction than staminate, with flowers set terminally on short lateral branches. Flowers have an irregular initiation sequence, with frequent abortions of organs. In Montinia, petals grow rapidly, and no zonal growth takes place. The gynoecium develops as a pit surrounded by a girdle. Placentation is basically parietal and becomes axillary by the postgenital fusion of placental lobes; unitegmic ovules are arranged in two parallel rows with adjacent ovules partly overlapping each other. Unisexuality is respectively attained at the stage of anther development and carpel initiation. The floral anatomy of pistillate and staminate flowers is illustrated and discussed. Observations on Montinia are compared with data of taxa from Saxifragaceae sensu stricto, Cornales, and Solanales. The absence of sympetaly in Montinia is discussed. Morphological and anatomical evidence points to a high similarity with Escalloniaceae. Although a position in the asterids is most probable, there is little support for the relationship with Solanales indicated by molecular data.     

An Examination of the Function of Male Flowers in an Andromonoecious Shrub Capparis spinosa

The pollen donor and pollinator attractor hypotheses are explanations for the functions of the male flowers of andromonoecious plants. We tested these two hypotheses in the andromonoecious shrub Capparis spinosa L. (Capparaceae) and confirmed that pollen production and cumulative volume and sugar concentration of nectar do not differ between male and perfect flowers. However, male flowers produced larger anthers, larger pollen grains and smaller ovaries than perfect flowers. Observations on pollinators indicated that two major pollinators (Xylocopa valga Gerst and Proxylocopa sinensis Wu) did not discriminate between flower morphs and that they transferred pollen grains a similar distance. However, there were more seeds per fruit following hand pollination with pollen from male flowers than from perfect flowers. Individuals of C. spinosa with a larger floral display (i.e. bearing more flowers) received more pollen grains on the stigma of perfect flowers. Female reproductive success probably is not limited by pollen. These results indicate that male flowers of C. spinosa save resources for female function and that they primarily serve to attract pollinators as pollen donors.     

THE INTRAFLORAL PHENOLOGY OF STREPTANTHUS TORTUOSUS (BRASSICACEAE)

The sequence of floral events during anthesis was examined in Streptanthus tortuosus to determine the relationship between the male and female floral phases. The flowers are strongly protandrous. In the staminate phase, the anthers mature sequentially over a 3–4-day period. Because pollinators quickly remove pollen from the anthers, sequential anther maturation prolongs the male phase relative to what it would be if anthers did not mature sequentially. Pollen applied to the stigma during the staminate phase does not adhere readily and does not germinate. The length of the pistillate phase depends on pollinator activity, as pollination accelerates the abscission of floral parts. Unpollinated flowers remain pistillate for 3–4 days, during which time stigmatic receptivity declines gradually. In the field, 72% to 80% of flowers are staminate at any time, indicating that the staminate phase is three times longer than the pistillate phase when pollinators have access to the flowers. The consequences of the relative length of the floral phases and the schedule of stigmatic receptivity are discussed in terms of outcrossing mechanism, floral longevity, and sexual selection models.     

Resource partitioning to male and female flowers of Spinacia oleracea L. in relation to whole-plant monocarpic senescence

Male plants of spinach (Spinacea oleracea L.) senesce following flowering. It has been suggested that nutrient drain by male flowers is insufficient to trigger senescence. The partitioning of radiolabelled photosynthate between vegetative and reproductive tissue was compared in male (staminate) versus female (pistillate) plants. After the start of flowering staminate plants senesce 3 weeks earlier than pistillate plants. Soon after the start of flowering, staminate plants allocated several times as much photosynthate to flowering structures as did pistillate plants. The buds of staminate flowers with developing pollen had the greatest draw of photosynthate. When the staminate plants begin to show senescence 68% of fixed C was allocated to the staminate reproductive structures. In the pistillate plants, export to the developing fruits and young flowers remained near 10% until mid-reproductive development, when it increased to 40%, declining to 27% as the plants started to senesce. These differences were also present on a sink-mass corrected basis. Flowers on staminate spinach plants develop faster than pistillate flowers and have a greater draw of photosynthate than do pistillate flowers and fruits, although for a shorter period. Pistillate plants also produce more leaf area within the inflorescence to sustain the developing fruits. The (14)C in the staminate flowers declined due to respiration, especially during pollen maturation; no such loss occurred in pistillate reproductive structures. The partitioning to the reproductive structures correlates with the greater production of floral versus vegetative tissue in staminate plants and their more rapid senescence. As at senescence the leaves still had adequate carbohydrate, the resources are clearly phloem-transported compounds other than carbohydrates. The extent of the resource redistribution to reproductive structures and away from the development of new vegetative sinks, starting very early in the reproductive phase, is sufficient to account for the triggering of senescence in the rest of the plant.     

The occurrence and structure of apparently bisexual flowers in the date palm, Phoenix dactylifera L. (Arecaceae)

Individuals of Phoenix dactylifera L. have expanded pistillodes or pseudocarpels in staminate flowers. These pseudocarpels are located in the centre of the male flowers and are surrounded by stamens. The gynoecium has the characteristic three carpellate arrangement commonly found in female date palm flowers. Pseudocarpels from male flower buds can expand into parthenocarpic fruit. Histology of the expanded pistillodes or pseudotarpels is similar to that of normal carpels from pistillate plants. These pseudocarpels lack ovules. Nutrient medium containing 10 mg 1^-1 of 2,4-dichlorophenoxyacetic acid or p-chlorophenylacetic acid and 0.3% activated neutralized charcoal enhanced the development and outgrowth of the pseudocarpels of cultured male flowers.     

Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.     

海滨锦葵花内五柱头裂片弯曲的独自调节(英文)

海滨锦葵花柱有5柱头裂片,若传粉失败,柱头裂片向下弯曲使柱头与自身花粉接触,发生延迟自交。传粉不足条件下发生的延迟自交可能提供繁殖保障。该研究定量分析了花粉搁置和授精胚珠数对花内未授粉柱头裂片运动的影响,并测定了花粉—胚珠比及柱头可授性和花粉生活力。结果表明,花内未授粉柱头裂片的弯曲不受其他柱头接受花粉量及授精胚珠数的影响,仅响应于其自身是否接受到花粉,花粉-胚珠比值显示海滨锦葵交配系统属兼性异交;未授粉柱头经弯曲与自身花粉授触时的强柱头可授粉和高花粉生活力为自交授粉的发生提供了可能。包括柱头裂片运动在内的多个花性状有机地展示了一种新花内混合交配系统,且花内柱头裂片弯曲的独自调节为从花水平验证被广泛接受的自交进化解释——繁殖保障假说提供了可能。     

Floral anatomy,embryology, seed,and fruit development in Cephalanthus (Naucleeae-Rubiaceae), with emphasis on C. glabratus

Information on the reproductive anatomy in genera of the tribe Naucleeae, particularly Cephalanthus, is scarce and fragmented. Of the six species in the genus, only the mature megagamethophyte of Cephalanthus occidentalis has been described. This study aims to provide information on embryological aspects in flowers of C. glabratus and to analyze the morphology and anatomy of the flowers, fruit, and seed in the six species of the genus. Cephalanthus glabratus have imperfect flowers: pistillate (PF) and staminate (SF). In the PF, the ovules are functional, while in the SF, they atrophy during the formation of the embryo sac. The mature ovule has a single integument, corresponds to the Phyllis type and the embryo sac is a Polygonum type, forming only in the PF. The presence of pollenkitt and secondary presentation of pollen were observed in the SF, as well as in the pollen formation previously described, whereas in the PF, they are absent, due to the collapse of the pollen grains inside the indehiscent anthers. The analysis of the ontogeny of the ovular excrescence in C. glabratus determined its funicular origin, calling it an aril. Its development is a pre-anthesis event, initiated during megasporogenesis. In seeds, the aril is a fleshy, white appendage which almost completely envelops the seeds of Cephalanthus, except for Cephalanthus natalensis where it is noticeably more reduced. Studies of the fruit in Cephalanthus species indicate that the infructescence is a dry schizocarp which separates into uni-seminated mericarps, except in C. natalensis that has fleshy indehiscent fruit.

     

Reproductive biology of Alpinia blepharocalyx (Zingiberaceae): another example of flexistyly

The floral biology and breeding system of Alpinia blepharocalyx were studied in Yunnan province, southwest China. Our results indicate that populations of A. blepharocalyx have two floral morphs, which differ in flowering behaviour: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther at afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon; the flowering period of both floral morphs is 12 hours; the stylar movements in the two floral morphs are synchronous, and they have similar traits to those found in other Alpinia species previously reported. Also, on average, cataflexistylous flowers are larger than anaflexistylous flowers, especially the labellum and corolla tube length; moreover, the P/O ratio of the two floral morphs is significantly different: the cataflexistylous morph has more pollen grains and fewer ovules than the anaflexistylous morph; the evolutionary significance of this comparison is discussed. Cataflexistylous flowers were observed to produce a lower concentration of nectar than that of anaflexistylous flowers before 11:00 a.m., but they then have higher nectar concentration; cataflexistylous flowers always have more nectar than anaflexistylous flowers. Flowers of A. blepharocalyx were visited by fewer insects at a lower frequency, including honey bees (Apis cerana cerana) and two species of carpenter bees (Xylocopa spp.). No significant differences were found in the fruit set among the hand-pollination treatments regardless of selfing (geitonogamy and autogamy) or crossing (intermorph and intramorph); but all hand-pollination treatments exhibited much higher fruit set than the controls; meanwhile, no fruit set occurred in the unpollinated bagged plants. Pollen tube growth was examined using fluorescence microscopy following self, intramorph, and intermorph hand pollinations at different times of the day; the pollen tubes of both floral morphs have the same growth rate and the capability to reach the ovary. Both the results of pollen tube growth and fruit sets under different pollination conditions show that A. blepharocalyx is self-compatible and dependent upon insects for pollination. The distinctive flexistyly mechanism of A. blepharocalyx is likely a floral mechanism that promotes effective intermorph pollen transfer.     

Flower structure and potential bisexuality in Freycinetia reineckei (Pandanaceae), a species of the Samoa Islands

In Freycinetia reineckei the staminate flower (on the staminate spikes) comprises 3 or 4 (sometimes 2) stamens and a pistillode with 2 (sometimes 4) carpellodes, and the pistillate flower (on the pistillate spikes) is formed of a pistil with 2 (sometimes 4) carpels and of 3 or 4 (sometimes 2) staminodes. This perfect floral homology, also observed in all the other species that were studied with both pistillate and staminate material, strongly suggests that the flower of Freycinetia is basically and potentially bisexual, and may explain the occasional sexual lability and bisexuality of that flower (occurrence of both pistillate and staminate inflorescences, and/or of bisexual inflorescences with bisexual flowers and/or unisexual flowers, on the same individuals) in some species, and also the frequent occurrence of bisexual spikes in this species. These may be partitioned into pistillate, staminate, mixed and sterile zones. In the pistillate zones the flowers have the same aspect and structure as the pistillate flowers. In the staminate zones the flowers generally comprise 3 or 4 (sometimes 2) stamens and a ‘semi-pistil’ some have both stamens and staminodes. The semi-pistils are intermediate between pistils and pistillodes in length, aspect and structure, but always have placentas and ovules. In the mixed zones the flowers are generally formed of a pistil and 3 or 4 (sometimes 2) stamens, and are therefore true hermaphrodite flowers; some have both stamens and staminodes. In the sterile zones the flowers comprise a semi-pistil and 3 or 4 (sometimes 2) staminodes. The staminodes are anatomically very similar to the stamens, especially in the staminate, mixed, and sterile zones, in which they exhibit a wide range of variation in length, aspect and structure. The perfect floral homology as generic character on one hand, and the occasional bisexuality both with and without bisexual flowers and other aspects of sex expression (e.g. occurrence of both pistillate and staminate shoots on the same individuals) in some species on the other hand, seem to indicate that Freycinetia is a basically monoecious, sex changing genus.