C. J. Webb

The avoidance of interference between the presentation of pollen and stigmas in angiosperms I. Dichogamy

Abstract Dichogamy is the separation of the presentation of pollen and stigmas in time within a plant. It is a common but neglected feature of outcrossing angiosperms. Dichogamy has been almost universally interpreted as an outcrossing mechanism, but many dichogamous species are also self-incompatible (and sometimes also herkogamous and/or with unisexual flowers). In outcrossing species, there is almost invariably a clash between selection to place pollen and stigmas in similar positions for effective pollination and selection to keep the androecia and gynoecia apart to avoid interference between them. We suggest that the separation of pollen and stigmas acts in general to reduce this self-interference and it often also reduces self-fertilisation. Mechanisms preventing self-fertilisation primarily increase maternal fitness, whereas mechanisms avoiding self-interference primarily promote paternal fitness. Five independent ways of subdividing dichogamy are recognised: protandry or protogyny; intrafloral or ...

Secondary sex characters in plants

SummarySexually dimorphic seed plants have partial or complete separation of ovule and pollen functions into two separate sexes, here uniformly called male and female. Secondary sex characters (differences between the sexes in structures other than the androecia and gynoecia) of such populations are reviewed.In a number of perennial species, males exceed females in vigor, growth rate or vegetative reproduction. In several monocarpic or short-lived polycarpic species, including hemp, spinach and species ofSilene, females are larger than males. In asparagus, males exceed females in total growth, but individual shoots of females are larger. In some long-lived species, the greater survival rate of males than of females contributes to a predominance of males, but in species ofSilene andRumex acetosa males have a higher mortality rate than females. Males and females sometimes have different microdistributions, and inMercurialis perennis andRumex acetosella this appears to be associated with different environmental optima of the sexes. Differences between males and females in habit, leaf characters and minor morphological features are described. In a considerable range of species, male inflorescences emerge or bolt earlier and males begin flowering sooner than females. Several authors have suggested that females spend proportionately more of their resources on sexual reproduction (have a higher reproductive effort) than do males. The only available data, those forRumex acetosella, support this. There are more reports of males flowering earlier in life and more frequently, having more numerous inflorescences and more flowers per inflorescence, than of females exceeding males in these features. Differences between individual male and female flowers are reviewed.Secondary sex characters may be incidental consequences of the developmental or genetic basis of sex determination and not adaptive themselves, or they may be selected as optimal strategies for the sexes, or both kinds of explanation may simultaneously be applied. We propose that many of the observed differences between the sexes are of direct selective value in relation to the distinct roles of males and females in sexual reproduction. In particular, the benefits to males of increasing pollen production and to females of increasing ovule production differ in such a way that the optimal reproductive effort will often be less for males than for females; this appears to explain a number of secondary sex characters.RésuméChez les spermatophytes sexuellement dimorphes, les fonctions de l’ovule et du pollen sont plus ou moins complétement séparées en deux sexes distincts, uniformément appelés ici mâle et femelle. Les caractères sexuels secondaires de populations de ce type (différences entre les sexes autres que celles relatives à l’androcée et au gynécée) sont passés en revue.Chez beaucoup d’espèces perennes, les mâles sont supérieurs aux femelles en vigueur et en vitesse de croissance ou de reproduction végétative. Chez plusieurs espèces monocarpiques comme chez plusieurs espèces annuelles polycarpiques, comme le chanvre, l’épinard ou certaines espèces deSilene, les femelles sont plus grandes que les mâles. Chez l’asperge, les mâles sont supérieurs aux femelles en biomasse totale mais les rameaux des femelles pris individuellement sont plus volumineux. Chez certaines espèces perennes, la longévité des mâles est supérieure à celle des femelles, de sorte que les mâles prédominent; cependant, chez les espèces deSilene et chezRumex acetosa, le taux de mortalité des mâles est plus élevé que celui des femelles.Les mâles et les femelles ont parfois des micro-distributions différentes, ce qui correspond, chezMercurialis perennis et chezRumex acetosella, à des conditions de milieu optimum différentes suivant les sexes. Sont décrites des différences entre mâles et femelles en port, en caractéristiques foliaires et en détails morphologiques divers. Pour une gamme très étendue d’espèces, l’apparition de l’inflorescence et la floraison ont lieu plus tôt chez les mâles que chez les femelles. Divers auteurs pensent que les femelles dépensent, en proportion, davantage de leurs ressources pour la reproduction sexuée (elles consentent un plus grand effort reproductif) que ne le font les mâles. Les seules données disponibles, qui concernentRumex acetosella, confirment ce point de vue. La littérature fournit davantage de cas où les mâles fleurissent plus souvent, ont des inflorescences plus nombreuses et davantage de fleurs par inflorescence que les femelles que de cas où l’inverse se produit.Des différences entre les fleurs des individus mâles et femelles ont été décrites concernant des caractères tels que la dimension des pétales, la production de nectar et les structures qui interviennent dans la reproduction des graines.Il se peut qu’un caractère sexuel secondaire soit la conséquence fortuite du mécanisme génétique ou ontogénique de la détermination du sexe et ne soit pas adaptatif par lui-même; il se peut aussi qu’il résulte de la sélection pour une stratégie optimum pour les sexes; il se peut enfin que les deux types d’explications s’appliquent à la fois. Nous avons tendance à penser que beaucoup des différences observées entre les sexes ont une valeur sélective directement rattachée aux rôles différents des mâles et des femelles dans la reproduction sexuée. En particulier, les bénéfices qui résultent de l’augmentation de la production de pollen par le mâle et de l’augmentation de la production d’ovules par les femelles diffèrent de telle façon que l’effort reproductif optimum est souvent moindre pour les mâles que pour les femelles. Ceci parait pouvoir expliquer l’existence de nombreux caractères sexuels secondaires.

The Selection of Heterostyly

Since heterostyly became well known over a century ago, botanists have consistently proposed that its adaptive significance lies in the encouragement it provides for outcrossing. Darwin (1877, p. 258) for example, wrote that “We may feel sure that plants have been rendered heterostyled to ensure cross-fertilization, for we know that a cross between the distinct individuals of the same species is highly important for the vigour and fertility of the offspring.” There has, however, been a variety of opinions expressed as to precisely how heterostyly ensures cross-fertilization.

Gender dimorphism in indigenous New Zealand seed plants

Abstract The frequent occurrence of gender dimorphism has long been recognised as one of the distinctive features of the New Zealand flora. We list 83 seed plant genera in which gender dimorphism occurs, and document habit, pollination, and dispersal characters for each genus. This means that gender dimorphism is represented in 23% of the genera in the flora; however, not all of these genera are uniformly dimorphic in gender—40% of them include some species or populations that lack gender dimorphism. We estimate that gender dimorphism has arisen autochthonously in 17 of the 83 genera— therefore, gender dimorphism evolved elsewhere in most cases (80%), and was established in New Zealand by subsequent migration. A comparison of the genera in which gender dimorphism occurs with the remainder of the flora shows that gender dimorphism is strongly correlated with fleshy fruits, and with woody habits. No correlation was found between gender dimorphism and pollination mode, perhaps because relatively unspecialise...

Phylogenetic relationships of species of Gingidia and related genera (Apiaceae, subfamily Apioideae)

Abstract Five genera of Australasian apioid Apiaceae (Gingidia, Scandia, Lignocarpa, Anisotome, and Aciphylla) have a complex taxo‐nomic history with the circumscription of, and inferred relationships among, the currently accepted genera based on only morphological characters. This molecular and phylogenetic study focuses on the relationships among the taxa currently included within Gingidia using the other genera as outgroups. Phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer region sequences for 17 species from these genera, and comparison with Smyrnium to root the trees, indicate that Gingidia is polyphyletic as currently circumscribed, the species belonging in two distinct monophyletic groups. However, morphological characters do not support these two groups, making taxonomic interpretation difficult. The monophyletic G. montana group includes the ditypic endemic genera Scandia and Lignocarpa, suggesting that they should not be maintained. The second monophyletic group include...

The reinstatement of Leptinella at generic rank, and the status of the ‘Cotuleae’ (Asteraceae, Anthemideae)

Abstract Leptinella Cass. has for more than one hundred years been relegated to sectional rank within Cotula L. All species of Leptinella are distinguished from those of the other two sections of Cotula, and other Anthemideae, by the conspicuous “inflated” corollas of the female florets and by chromosome numbers based on x = 26 where known; most species are also distinguished by a suite of habit characters. Of the genera at times included in the ‘Cotuleae’, only Soliva sens. lat. is clearly related to Cotula; most other genera have been referred to other tribes or are of uncertain affinities. The relationship of Leptinella to Cotula sect. Cotula and sect. Strongylosperma, and to Soliva remains unclear, but Leptinella is undoubtedly monophyletic and is sufficiently distinct to warrant recognition at generic level. We reinstate the genus Leptinella and make all necessary combinations. Leptinella is a genus of 33 species distributed in New Guinea, Australia, New Zealand, the Subantarctic Islands, and South A...

A rose by any other name: Two problems of scent in the naming and typification of New Zealand plants

Abstract For two New Zealand species, the plant names are inappropriate references to the scent of the plant. Both result from misinterpretation of earlier work and are resolved here. Firstly, Banks & Solander originally applied the epithet aromatica to the species now known as Scandia rosifolia not to Anisotome aromatica, but as their manuscript was not published current usage is retained. Secondly, following the Forsters, the type species of Coprosma is correctly designated as C. foetidissima not the inappropriately scented C. lucida; subgeneric and sectional names are corrected.

SPELLING NEW ZEALAND IN THE SPECIFIC AND INFRASPECIFIC EPITHETS OF VASCULAR PLANTS

Abstract There is confusion in the botanical literature over the correct forms of epithets used to refer to the country of New Zealand. A table giving original spellings of all specific and infraspecific taxa of vascular plants named after New Zealand is provided, along with corrected spellings and the reasons for these. It is suggested that new names would be more helpful if they were based on character states or habitats that distinguish the taxa being named.

The breeding system of Pennantia baylisiana (Icacinaceae)

Abstract Murray & de Lange (1995) suggested that, as a seedling grown from a seed of the single known wild tree of Pennantia baylisiana appears to have arisen by normal sexual processes, “this must cast some doubt on the reports that this species is dioecious and that the only wild plant is female…”

The reinstatement of Utricularia protrusa for New Zealand and an assessment of the status of the other New Zealand bladderworts based on seed characters.

Abstract Taxonomic views of the genus Utricularia (Lentibulariaceae) as it occurs in New Zealand have changed considerably since the publication of Volume 1 of the Flora of New Zealand in 1961. Examination of the seeds of the New Zealand bladderworts has assisted in further clarifying the status of some species but provides no assistance with others. We now accept three indigenous species for New Zealand: U. protrusa (the name reinstated for plants recently erroneously referred to as U. australis), U. delicatula (a New Zealand endemic distinct from the Australian U. lateriflora), and U. novae-zelandiae (including U. monanthos). The name U. gibba (instead of U. biflora) is accepted for the single naturalised species.