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 ...

https://www.tandfonline.com/doi/pdf/10.1080/0028825X.1986.10409726

The avoidance of interference between the presentation of pollen and stigmas in angiosperms II. Herkogamy

Thome, Robert F. (Rancho Santa Ana Botanic Garden, Claremont, CA 91711). Classification and geography of the flowering plants. Bot. Rev.58(3): 225–348. 1992.—This treatment of the flowering plants is the latest revision of my classification of the Class Angiospermae and replaces my 1983 and more recent 1992 synopses. An update is necessary because so much new information has been published in the last decade pertinent to the classification of the flowering plants. About 870 such recent books, monographs, and other botanical papers are cited in the Introduction, listed primarily by the botanical discipline that they represent. Also considerable changes in my classification have been necessitated by my narrowed family- and ordinal-gap concepts, acceptance of the ending “-anae” for superorders in place of the traditional but inappropriate “-iflorae,” and acceptance of more prior or more widely used names for the categories above the family. A new phyletic “shrub” replaces earlier versions, and attempts to indicate visually relative sizes and relationships among the superorders, orders, and suborders. One table includes a statistical summary of floweringplant taxa: ca. 233,900 species of 12,650 genera, 437 families, and 708 subfamilies and undivided families in 28 superorders, 71 orders, and 71 suborders of Angiospermae. Three other tables summarize the known indigenous distribution of the families and subfamilies of angiosperms about the world. The synopsis lists the flowering plant taxa from the class down to the subfamily (and in Asteraceae down to the tribe) with indication of the degree of confidence I place in the circumscription and placement of each category above the subfamily, the best available estimates of the number of genera and species for each category, and the known indigenous distribution of each subfamily and family. Table V lists alphabetically the geographical abbreviations used in the synopsis. The extensive bibliography of recent literature should be helpful to those persons interested in the classification of the flowering plants.

https://link.springer.com/content/pdf/10.1007/BF02858611.pdf

Classification and geography of the flowering plants

A century of research on heterostylous plants has passed since the publication of Charles Darwin's book "The Different Forms of Flowers on Plants of the Same Species" in 1877 summarizing his extensive observations and experiments on these complex breeding systems involving genetic polymorphisms of floral sex organs. Since then, heterostylous plants have provided a rich source of material for evolutionary biologists and today they represent one of the classic research paradigms for approaches to the study of evolution and adaptation. This book offers a detailed account of the subject. In 10 chapters it is concerned with the evolution, genetics, development, morphology and the adaptive significance of heterostyly. Broad syntheses of research on heterostyly as well as new theoretical ideas and experimental data are included.

Evolution and function of heterostyly

Studies of mating patterns of tropical trees, typically involving common species, have revealed that most species are outcrossed and that, in some cases, a significant fraction of outcross pollen moves long distances. We evaluated mating systems and effective pollen dispersal for three hermaphroditic, insect-pollinated Neotropical tree species, Calophyllum longifolium, Spondias mombin, and Turpinia occidentalis, all of which occurred at low adult densities at the study site. Mating patterns were estimated for each maternal tree within 84-ha populations of C. longifolium and S. mombin in 1992 and 1993 and within a 50-ha population of T. occidentalis in 1993. Each population was 100% outcrossed. Multilocus paternity exclusion analyses indicated that in C. longifolium, a minimum of 62% of effective pollen moved at least 210 m. For S. mombin, estimates of apparent pollen flow greater than 300 m were 5.2% and 2 5% in 1992 and 1993, respectively. For all species, pollen dispersal was strongly affected by the sp...

Pollen dispersal in low-density populations of three neotropical tree species

Heterostyly is a genetic polymorphism in which plant populations are composed of two (distyly) or three (tristyly) morphs that differ reciprocally in the heights of stigmas and anthers in flowers (Fig. 1). The style-stamen polymorphism is usually accompanied by a sporophytically controlled, diallelic self-incompatibility system that prevents self- and intramorph fertilizations, and a suite of ancillary morphological polymorphisms, particularly of the stigmas and pollen of floral morphs. Heterostyly is reported from approximately 25 angiosperm families and has usually been viewed as a floral device that promotes outcrossing, hence reducing the harmful effects of close inbreeding in plant populations.

Heterostylous Genetic Polymorphisms: Model Systems for Evolutionary Analysis

Decaspermum parviflorum is a common shrub or treelet in clearings in eastern Sulawesi, Indonesia. It is widely distributed in SE Asia. It produces numerous white flowers and small blue-black fruits. Individual shrubs were of two types in 1:1 ratio, one bearing staminate flowers, the other bearing flowers with both stamens and carpels. The ‘hermaphrodite’ flowers were shown to have sterile pollen so the species is functionally dioecious. The flowers and floral sprays of the two sexes differed in several measurements: the male flowers had more anthers and were larger and more numerous, making the corporate visual image of male sprays more than twice as large as that for sprays of female flowers. Flowers, individuals of which last only one day, opened only every second day, when all bushes flower synchronously. When the anthers burst in the morning, pollen and sterile pollen was collected vigorously by a variety of bees, mostly Apis dorsata and Nomia spp. Most of the pollen was collected within 1 h of anthesis. Anthesis in males takes place about 20 min earlier than in females; insect visitation follows this pattern. The minute quantity of nectar was collected by only few insects and mostly after the pollen had gone, if at all. Fruits were eaten by birds. The species displays many features typical of dioecious tropical plants with the unusual feature of pollen being the main food reward for pollinators. It was pollinated effectively in Sulawesi.

Pollination in a cryptically dioecious plant Decaspermum parviflorum (Lam.) A. J. Scott (Myrtaceae) by pollen‐collecting bees in Sulawesi, Indonesia

On the reproductive biology of a canopy tree, Syzygium syzygioides (Myrtaceae), in a rain forest in Sulawesi, Indonesia

Polygala vulgaris is a widespread perennial plant species of basic to neutral grassland throughout Britain. It is variable in flower colour and some vegetative characters in most populations. Gene flow is restricted in all populations since the plants are normally self-pollinating (up to 20% outcrossing, calculated from figures of heterozygosity) and seeds are normally dispersed only up to 2 m from the parent plant. Examination of several enzyme systems, using starch gel electrophoresis, showed that all enzyme loci appeared to have been duplicated, probably owing to the fact that P. vulgaris is a tctraploid in a genus which has primarily diploid members in Europe. Polymorphisms were found at both of the duplicated loci in four enzyme systems and at one locus in each of two further systems.



Fifty-one populations from a diversity of habitats were sampled in southern Britain. In most populations from the typical habitat of lowland calcareous grassland, polymorphisms occurred at five or more loci, and the alleles were distributed throughout the populations. In all these sites there was a diversity of microhabitat and, in one area, marked differences in microhabitat distribution between different enzyme morphs. It is likely that differential selection is an important factor in the maintenance of the polymorphisms in all these areas. These populations were divided, genetically, into two main groups, those from the Gower peninsula, South Wales, and those from the English chalk. Within each group the populations were quite closely related genetically, though some large differences at particular loci occurred even between adjacent populations. Diffuse clumps of alleles occurred within all these populations, and it is likely that limited gene flow has affected the genetic structure of the populations, particularly since cycles of local extinction and recolonization are likely to be recurring. The genetic structure of each population, at the allozyme loci examined, is likely to be the consequence of a balance between differential selection and restricted gene flow. The number of heterozygotes was small, though higher than expected from an analysis of experimental progeny, suggesting a hcterozygotc advantage. Few strong multilocus associations were found despite the predominance of self-pollination.



In the populations from sand dunes, roadsides, submontane grassland and water meadows there was, in general, much less polymorphism than in those from lowland calcareous grassland and some populations were entirely monomorphic; in most others there were large, entirely monomorphic groups of plants. Genetic distances between these populations were variable, even within one habitat and area, and they did not appear to show any particular relationship to each other. It is likely that the genetic structure of these populations, at the loci studied, has arisen largely through chance colonizations and genetic drift.

Andrew J. Lack

Papers

Pollination in a cryptically dioecious plant Decaspermum parviflorum (Lam.) A. J. Scott (Myrtaceae) by pollen‐collecting bees in Sulawesi, Indonesia

On the reproductive biology of a canopy tree, Syzygium syzygioides (Myrtaceae), in a rain forest in Sulawesi, Indonesia

Allele frequencies, genetic relationships and heterozygosity in Polygala vulgaris populations from contrasting habitats in southern Britain.

The reproductive biology of a distylous tree, Sarcotheca celebica (Oxalidaceae) in Sulawesi, Indonesia