Pistillate Individuals Research Articles

Unraveling the development behind unisexual flowers in Cylindropuntia wolfii (Cactaceae)

BackgroundIn certain unisexual flowers, non-functional sexual organs remain vestigial and unisexuality can be overlooked leading to the ambiguous description of the sexual systems. Therefore, to accurately describe the sexual system, detailed morphological and developmental analyses along with experimental crosses must be performed. Cylindropuntia wolfii is a rare cactus endemic to the Sonoran Desert in southern California and northern Baja California that was described as gynodioecious by morphological analysis. The aims of our project include accurately identifying the sexual system of C. wolfii using histological and functional studies and characterizing the developmental mechanisms that underlie its floral development.MethodsHistological analyses were carried out on different stages of C. wolfii flowers and controlled crosses were performed in the field.ResultOur results identified C. wolfii to be functionally dioecious. The ovule and anther development differed between staminate and pistillate flowers. In vivo pollen germination tests showed that the pollen of staminate and pistillate flowers were viable and the stigma and style of both staminate and pistillate flowers were receptive. This suggests that there are no genetic or developmental barriers in the earlier stages of pollen recognition and pollen germination.ConclusionsDespite being functionally dioecious, we observed that functionally pistillate individuals produced fruits with a large number of aborted seeds. This implies that not only does this species have low reproductive success, but its small population sizes may lead to low genetic diversity.

Playing the Taxonomic Cupid: Matching Pistillate and Staminate Conspecifics in Dioecious Clusia (Clusiaceae)

Abstract—Dioecious reproduction, in which unisexual flowers are developed in separate individuals, is an uncommon characteristic that has evolved multiple times independently in angiosperms. Nearly all species in the neotropical genus Clusia are dioecious and most of them are incompletely known because only one sexual morph, either the staminate or the pistillate individual, has been described. Here we explored the variability in chloroplast regions atpF intron, matK, ndhA intron, petL-psbE, rpl16 intron, as well as the nrDNA ITS to evaluate conspecificity between staminate and pistillate individuals within the genus Clusia. Our results indicate that phylogenetic analyses using maximum likelihood and Bayesian inference based on nrDNA ITS data is a suitable approach to assess whether sexual morphs are conspecifics and to estimate species phylogenetic position within the genus. Staminate and pistillate individuals were effectively identified for Clusia araracuarae, C. lundellii, C. stenophylla, and C. uvitana. Distribution maps as well as full morphological descriptions for these species are provided along with comments on their phylogenetic relationships.

Transfer of the perfect flower trait fromPoa secundatoPoa arachnifera

A Texas bluegrass (Poa arachnifera) population has been developed that successfully integrates the perfect flower trait from Poa secunda through interspecific hybridization. The resulting perfect flowered P. arachnifera population is perennial, rhizomatous and lacks the cobweb-like hairs that are a typical characteristic of the P. arachnifera parent. Inheritance of the perfect flowered trait suggests a relatively simple inheritance, perhaps allelic to the segregation of staminate and pistillate individuals in other dioecious systems. This material may have applications as a clean seeded, perfect flowered P. arachnifera cultivar; or as a germplasm resource in a P. arachnifera breeding program.

Cabralea canjerana subsp. polytricha (Adri. Juss.) Penn. (Meliaceae), uma espécia diótica

O estudo foi realizado em áreas de cerrado do Clube Caça e Pesca Itororó em Uberlândia-MG, durante os meses de setembro de 1997 a novembro de 1998. Para confirmação da suspeita da ocorrência de dimorfismo sexual foram adotados vários procedimentos: análise morfológica da flor de indivíduos supostamente dimórficos, análise de viabilidade polínica, medidas de altura dos indivíduos e do comprimento das inflorescências e determinação do sistema reprodutivo com realização de experimentos de polinização. Os resultados dos tratamentos florais e da análise de viabilidade polínica revelaram o caráter dióico dos indivíduos estudados. Os morfos sexuais diferem significativamente quanto à altura (F=11,01; P<0,001) e quanto ao comprimento das inflorescências (F=240,82; P<0,005), sendo, em ambos os casos, maiores nos indivíduos pistilados. A formação e posterior desenvolvimento de frutos só foram observados em tratamentos de polinização cruzada, realizados entre indivíduos estaminados e pistilados (exceção para um caso em 900 tentativas). Entretanto, a observação de frutos produzidos naturalmente por um aparente "fenótipo masculino", indica que o processo de evolução da dioicia nesta espécie ainda não foi concluído. A polinização é feita por uma espécie de vespa Polistes e por abelhas Xylocopa e Exomalopsis.

Geographic parthenogenesis in a tropical forest tree

As evidenced by embryological studies, certain tropical tree species can reproduce asexually via seed; however, it has generally been assumed that such apomictic reproduction is facultative. Here I report the existence of a population of the lowland Malaysian rain forest tree Garcinia scortechinii King that consists entirely of pistillate individuals (40 female trees and no male trees recorded within a 25-ha area). This constitutes the first documented observation of a geographically segregated, obligately asexual population among wild tropical trees. Six additional Garcinia species showed a trend toward female bias relative to other dioecious tree species studied, an observation that is consistent with facultative apomixis. The more surprising result for G. scortechinii runs counter to the generalization that obligate apomicts occur only in environments in which the absence of competitors might enable persistence of taxa that lack genetic recombination through mixis.

Pollen movement to flowering canopies of pistillate individuals of three rain forest tree species in tropical Australia

AbstractThis study measured the quantities of effective pollen vectors and their pollen loads arriving at the canopies of dioecious tropical rain forest trees in north‐east Queensland. Population flowering synchrony, effective pollinator populations and pollen loads transferred between staminate and pistillate trees were compared among three insect‐pollinated tree species. All three were visited by a wide range of insects, 75% of which (mostly 3–6 mm long) carried conspecific pollen. Fewer than 8% of individual insects were found to be carrying single‐species pollen exclusively and none could be described as specialist pollen foragers. The introduced honeybee carried greater quantities of pollen than any native species but was not necessarily a reliable pollinator.The brief flowering periods in Neolitsea dealbata (3–4 weeks) and Litsea leefeana (4–5 weeks) populations were synchronized among individuals. Flowering in the Diospyros pentamera population extended over 15 weeks and most individuals were in flower for most of this period. Staminate trees began flowering earlier, produced more flowers and attracted relatively more insects than did pistillate trees, suggesting a density‐dependent response of pollinators to flowering performance. Pollen was trapped in greater quantities on insects at staminate trees than at pistillate trees.Insect numbers increased at peak flowering periods and Diptera were the most abundant flower visitors. Anthophilous Coleoptera were more numerous at staminate than at pistillate trees in all three tree species populations. Larger quantities of pollen were mobilized during peak flowering times although the greatest quantities were transferred to pistillate canopies towards the end of the population flowering periods. Diptera carried pollen more often to pistillate N. dealbata and L. leefeana trees than did other groups whereas Coleoptera carried pollen more often to pistillate D. pentamera trees. The two contrasting flowering performances in the three tree species are discussed with reference to mechanisms that facilitate pollen transfer between staminate and pistillate trees.

New and Noteworthy Species of Hechtia (Bromeliaceae) from Guerrero, Mexico

Two new species are described in the genus Hechtia: H. carlsoniae and H. pumila. Hechtia melanocarpa, previously thought to be known only from its type, is represented by several collections. In contrast to the type specimen which is of horticultural origin, collections from the type locality have consistently larger inflorescences with elongate lateral branches. Moreover, sta- minate and pistillate individuals differ significantly in inflorescence form and petal shape. Hechtia Klotzsch is a genus of about 50 species

The Adaptive Significance of Sexual Lability in Plants Using Atriplex canescens as a Principal Example

The Adaptive Significance of Sexual Lability in Plants Using Atriplex canescens as a Principal Example

THE SELECTIVE ADVANTAGE OF STAMINATE HETEROGAMY

In a series of now classic experiments, Jones (1932) was able to demonstrate that as few as two mutations would suffice to convert Zea mays to dioecism. His studies were of particular interest in that they revealed that pistillate or staminate heterogamy could evolve with equal facility. On the basis of this information, there would seem to be no reason to anticipate that within dioecious angiosperms, one sex, more often than the other, should be characterized as the heterogametic sex. Yet a survey of the literature will indicate that in dioecious species, staminate individuals, to a very large extent, represent the heterogametic sex. Westergaard (1958), for example, refers to 13 families in which the genetics of sex determination is fairly well understood. In 11 of these families, all dioecious species studied were characterized by staminate heterogamy. Within a twelfth family, the Caryophyllaceae, some strains, but not all, of Silene otites may possess heterogametic pistillate individuals, while in Silene alba and S. dioica staminate plants are XY, pistillate XX. Fragaria (Rosaceae) is the only known genus in which all dioecious species studied definitely possess pistillate heterogamy. This preponderance of staminate heterogamy cannot be attributed to a common origin as might be the case among the Mammalia because, within the angiosperms, dioecism appears to be a short-lived and sporadic method of promoting outbreeding (Darlington, 1958). Westergaard (1958) considers that in a majority of cases, the evolution of dioecism has apparently taken place on the species level. It thus seems all the more remarkable that staminate heterogamy, if possessing no selective advantage relative to the alternative, should characterize so many examples of dioecism. However, recent studies, the results of which will be presented here in summarized form, have demonstrated that a mechanism, described by Correns (1928) and dependent upon staminate heterogamy, confers a positive selective advantage on a dioecious species possessing it. Working with Silene alba (Melandrium album), a dioecious species in which staminate plants are heterogametic, Correns saw that crosses in which small amounts of pollen were used produced approximately equal proportions of staminate and pistillate offspring. If, however, large amounts of pollen were used, the progenies contained a greater than expected proportion of pistillate plants. Correns reasoned that the pollen tubes containing an X (or pistillate determining) chromosome grew faster than did those containing a Y chromosome. Thus if large amounts of pollen were available, the faster growing X pollen tubes could reach and enter more than half the ovules while the Y pollen tubes were still penetrating the style. With only a little pollen available, the X pollen tubes would still be first in reaching the ovules but a sufficient number of eggs would remain unfertilized to accommodate the slower Y pollen tubes, resulting in approximately equal proportions of pistillate and staminate plants. The same mechanism was later observed in Rumex acetosa (Correns, 1928) and in Humulus japonicus (Kihara and Hirayoshi, 1932), both of which possess staminate heterogamy. The present study was designed to determine if this mechanism is of any significance

Studies on Ambrosia: III. Pistillate Ambrosia elatior x A. trifida and Its Bearing on Matroclinic Sex Inheritance

1. Pistillate plants of A. elatior always yield a mixed progeny of monoecious plants, intergrades, and pistillate individuals, irrespective of the genotype of the pollen parent. 2. Pistillate plants were crossed with A. trifida, which is strictly monoecious in nature. Seven hybrids were secured: two pistillate, four intergrades, and one normal monoecious. 3. The hybrids had approximately 30 somatic chromosomes (A. trifida n = 12, A. elatior n = 18). The first meiotic division was extremely irregular and involved primarily a separation of autosynaptic mates and a random segregation of univalents. The second division was regular and equational.

Secondary sex characters inAsparagus officinalisL.

does not appear. First page follows. Introduction Common asparagus is normally dioecious. Casual observations in the field reveal no striking differences between the two sexes in their vegetative characters. Careful studies, however, show that there are significant quantitative differences between staminate and pistillate individuals. Secondary sex characters in plants are far less striking than they are in animals. It is probably for this reason that they have received so little attention. Cowles(1) calls attention to the fact that “immediately after flowering it often is possible to distinguish at some distance pistillate from staminate mulberry trees by their much smaller leaves, as though the constructive material in the former were utilized chiefly in fruit development, and in the latter, in leaf development.” Later in the season, the leaves are equally large on both pistillate and staminate individuals. Guinier(3) states that dioecism in the case of Pinus montana and P. sylvestris is accompanied by a certain vegetative dimorphism. In purely staminate individuals, the branches terminating in inflorescences have the cones distributed over the greater part of the new shoots, a relatively small area being left at the apex for the short, leaf-bearing twigs. After these male cones have fallen, there is left a long bare section at the base of each new shoot, the leaves forming a tuft at the tip of the shoot.