Floral polymorphism in Polygonum bistorta L.

In the present study, new type of floral polymorphism (tristylous-like flowers) in Polygonum bistorta L., i.e., L-, M-, and S-styles (long, medium and short, respectively) is reported. This tristylous was not only present in different populations but also in a single inflorescence. Although the heights of styles and anthers in the three morphs of flowers differed, their ancillary tepal size, pollen polymorphism, and stigma polymorphism were found similar. The ratio of M-flowers was far lower than those of L- and S-flowers. Unlike the solid nectar of other Polygonum species, fluid nectar was present in Polygonum bistorta, which reflects its specialized state. Different from most of other hetereostylous species with tubular flowers and Polygonum jucundum with open distylous flowers, Polygonum bistorta contains semi-open flowers. Our findings suggest that P. bistorta represents special floral polymorphism in Polygonum and is an ideal plant species for studying the evolution of floral breeding system in Polygonum.Bangladesh J. Plant Taxon. 25(1): 1-11, 2018 (June)

Reproductive studies in ipecac (Psychotria ipecacuanha (Brot.) stockes; Rubiaceae): pollen development and morphology

The aim of this work was to carry out the reproductive studies on Brazilian accessions of ipecac, Psychotria ipecacuanha. It presented heterostyly, with brevistylous and longistylous flowers. The pollen development was observed from the sections of the anthers embedded in resin. Anther development was normal as usually observed in dicotyledones, displaying four layers: outer epidermis, endothecium, middle layer and inner tapetum. The pollen was bicellular and filled with starch at the microspore stage. Pollen morphology was studied using SEM, which showed pollen polymorphism within and between the two floral morphs. Five types of pollen with reticulate or perforate exine were identified. The characteristics showed that the sexual process was as important as the vegetative propagation for the reproduction of this species.

Pollen polymorphism in Thymus capitatus (Lamiaceae)

Polymorphism with respect to size and structural characteristics occurs in pollen grains of several species. Pollen grains of Thymus capitatus (L.) Hoffmans & Link. from three different areas of Greece were collected, and their palynological characteristics were measured. Using light and scanning electron microscopy, a quantification of pollen polymorphism of T. capitatus was achieved by measuring the size and the characteristics of exine sculpture. The measurements were repeated during 3 successive years, and statistical analyses with one-way ANOVA and Duncan’s multiple range test were applied. Results revealed differences in the exine pattern between the locations; also, three palynological characteristics (surface, perimeter, and equatorial diameter) differed statistically. The results clearly indicate that pollen grains of T. capitatus are polymorphic between the sampling areas. The polymorphism has been related to environmental parameters and mainly with water availability. Average rainfall seems to be the main factor contributing to the morphological variation of pollen grains by affecting their size and exine sculpture.

Quantitative evaluation of pollen polymorphism in a tristylous weed, Lythrum salicaria (Lythraceae)

Tristylous breeding system consists of three different forms of flowers that differ reciprocally in the heights of stigmas and anthers within flowers. Apart from the style and stamen lengths, heterostylous species also demonstrate pollen and stigma polymorphisms. Tristylous Lythrum salicaria L. bears trimorphic, striate, tricolporate pollen with three true colpi and three pseudocolpi. Using a scanning electron microscope, we quantified pollen polymorphism in L. salicaria by measuring the length and diameter of pollen, and the length of colpi and pseudocolpi. Pollen grains from the long stamens are significantly larger than those from the mid stamens, followed by those from the short stamens. Despite significant differences in pollen size among long, mid, and short stamens, pollen morphometric traits demonstrate overlap among morphs. Pollen diameter also differed significantly between source populations. A discriminant function analysis separated long-level pollen from mid- and short-level pollen based on the canonical scores of measurements of pollen structure. The polymorphism of pollen in conjunction with that of the stigma may play a functional role in self-incompatibility mechanisms.Key words: Lythrum salicaria, purple loosestrife, Lythraceae, heterostyly, incompatibility, pollen polymorphism.

Polymorphisme pollinique et polymorphisme génétique

The polymorphism of the exine of pollen grains was studied in different species to determine if it has a genetic component at the intraspecific level. For some species, the results show that significant differences exist between individuals and that the composition of populations can also vary. The authors conclude that the study of pollen polymorphism could increase our understanding of pollen evolution and the mechanisms of pollen – stigma interactions. Key words: polymorphism, pollen, ash, Rumex, iris.