The structure and ultrastructure on floral nectaries of Heliocarpus popayanensis Kunth. and Luehea divaricata Mart (Malvaceae-Grewioideae) were investigated for the first time. The floral nectaries of the analysed species are structured (can be recognised macroscopically and microscopically) and of trichomatic type. Significant morphological differences were observed between the nectaries of perfect and pistillate flowers of H. popayanensis, as well as between nectaries of this species and those of the related species, Triumfetta rhomboidea Jacq. The volume of nectar produced in the perfect and pistillate flowers of H. popayanensis and in the perfect flowers of L. divaricata presents significant differences that could be related to the rewards offered to flower visitors. No differences were observed in ultrastructure features of the glandular trichomes between H. popayanensis and L. divaricata. Nectar accumulation occurs between the wall and the cuticle. The predominant floral visitors in perfect and pistillate flowers of H. popayanensis were bees, and less frequently flies; whereas for L. divaricata were wasps, bumblebees, butterflies and beetles. Our results support the inclusion of each genus in different tribes according to the recent tribal classification based on molecular and morphological data of the subfamily Grewioideae.

The aim of this study was to analyze the pollen morphological diversity among nineteen species of the Adesmieae and Aeschynomeneae tribes with the purpose to evaluate its importance for the taxonomical delimitation of the Argentinean species and its systematic significance. Observations and measurements were performed on acetolyzed pollen grains. The samples were examined under light and scanning electron microscopes. Principal components analysis (PCA) and Conglomerates Analysis were performed for quantitative morphological variables. Adesmieae tribe is stenopalynous while Aeschynomeneae tribe is eurypalynous, pollen grains are 3-colporate, they have lolongate, circular or lalongate endoapertures, semitectate-reticulate or tectate-perforate, fossulate, supra-rugulate exine, small to large size, and suboblate to prolate shapes. A key was made to identify and distinguish species of Adesmia, Aeschynomene, Chaetocalyx, Discolobium, and Poiretia. Exine sculpture and structure, operculum presence, exine thickness, pollen shape, endoaperture shape, and pollen size all had taxonomic importance to distinguish the species inhabiting Argentine. The groupings recognized in recent classifications were hard to delimit on the basis on the palynological knowledge at this time since there are different pollen types but various of them occur among the three subclades. A framework for future evolutionary analyses within the dalbergioid clade was thus provided.

Anther development, microsporogenesis and microgametogenesis of six species of the genera Corchorus, Heliocarpus , Luehea and Triumfetta were analysed. The genera were found to share the following characters: ontogeny of anther wall of basic type; simultaneous microsporogenesis, resulting mainly in tetrahedral tetrads; secretory tapetum and pollen grains shed at the bicellular stage. Moreover, the characters that differentiate them are: presence of uninucleate tapetal cells in Heliocarpus and Triumfetta ; binucleate cells in Corchorus and multinucleate cells in Luehea ; differentiation of the thickenings of the endothecium at free microspores stage in Corchorus , Heliocarpus and Triumfetta , whereas in Luehea differentiation occurs at the mature pollen grains stage; late disintegration of sporogenous tissue cell walls in Luehea ; and the presence of orbicules, absent only in Corchorus . This is the first embryological report of the Grewioideae subfamily, contributing to the characterization of the genera studied. The results are discussed in relation to the known data for the family.