RESUMO
Alicia anisopetala and Callaeum psilophyllum are two closely related species that belong to the christianelloid clade of the family Malpighiaceae. Both species are pollinated by oil-collecting bees and exhibit variations at specimen and population level in the number of elaiophores per flower. These floral glands that secrete non-volatile oils constitute an ancestral trait for the family. There is evidence that the observed variations in the number of elaiophores can be the result of processes of connation or reduction associated with differences in their vascularization. In order to identify which process occurs in each species, we conducted an anatomical study in natural populations of both species distributed along a wide range of their geographical distributions in Argentina. We collected flowers of different individuals, counted the number of elaiophores per flower, carried out exomorphological observations, and used conventional histological techniques to examine the vascularization of these glands. The floral anatomy of both species does not show any modifications in other whorls related to the fusion or reduction of elaiophores. Our results indicate that the process of loss of elaiophores in A. anisopetala is caused by incomplete connation and in C. psilophyllum by reduction, suggesting that the processes that lead to the loss of elaiophores in Malpighiaceae are homoplastic and would not reflect phylogenetic signals.
RESUMO
Ovule morphology, megasporogenesis, and megagametogenesis processes were examined in Hydrocleys nymphoides, Alisma plantago-aquatica, and Sagittaria montevidensis. Each of these species belongs to a different clade within the Alismataceae family. It is worth mentioning that the genus Hydrocleys previously belonged to the Limnocharitaceae family but is now classified within the Alismataceae. Flowers in different developmental stages were processed following classical histological methods for their observation with bright-field microscope. The three species present an anatropous and bitegmic mature ovule. This is tenuinucellate in A. plantago-aquatica and S. montevidensis and pseudo-crassinucellate in H. nymphoides. Although all three species have the same type of megasporogenesis, they differ in the megagametogenesis and in the total number of nuclei and cells that form the mature gametophyte. H. nymphoides has a female gametophyte composed of four cells and four nuclei, while A. plantago-aquatica and S. montevidensis have a female gametophyte of five cells and six nuclei. The results are discussed according to the phylogenetic position of each of the species. Moreover, new types of megagametophyte development are described: Hydrocleys and Sagittaria types. The reduction of the female gametophyte with respect to the Polygonum type is found in families belonging to the ANA grade and in other aquatic families within the order Alismatales. We infer that the reduction in the number of cells and nuclei in the female gametophyte is characteristic of species that inhabit aquatic environments. Future studies in aquatic species belonging to other families would be necessary to confirm this hypothesis.
Assuntos
Sagittaria , Sagittaria/citologia , Óvulo Vegetal/citologia , Alisma/química , Alisma/citologia , Alismataceae/citologiaRESUMO
Although the presence of scent was described for several species of Rhamnaceae, localization, morphology and structure of osmophores were unknown. We studied different species of the tribes Rhamneae (Rhamnoids clade), Pomaderreae, Colletieae, Paliureae (Ziziphoids clade) and the species Alphitonia excelsa (unknown tribe, Ziziphoids clade). We expect to have a better comprehension of these structures and provide information on which morphological and anatomical characters may support the phylogeny of the family. We localized the osmophores in the margins and top of the sepals using neutral red. Histochemical tests were made on transverse hand-cut sections of fresh sepals. Observations were made with stereoscopic and bright field microscopes, scanning and transmission electron microscopes. Papillae were observed in the zones with positive reaction to reagents. Different kinds of hairs are present in the sepal epidermis besides papillae. Epidermal cells present a striate cuticle with canals and cavities. Druses are abundant in most species. The ultrastructure of epidermal and subepidermal cells shows high metabolic activity: there are vesicles, mitochondria, endoplasmic reticulum, dictyosomes, plastids with lipids and starch. The vascularization is well developed and reaches the top of the sepal where the principal area of volatile components production is localized. The location and abundance of papillae are the most important traits that allow us recognize and characterize the osmophores in Rhamnaceae. There are no clear anatomical and morphological features exclusive of one clade or tribe. Therefore, in contrast to other sporophytic structures of this family, osmophores do not seem to have any systematic value.