Embriologia de Acicarpha bonariensis (Pers.) Herter (Calyceraceae)

Abstract

The embryology of Calyceraceae is poorly known, mainly, concerning the anther development. To increase this knowledge and improve the understanding of the life history, diversity, and evolution of Asterales, we studied the embryology of Acicarpha bonariensis (Pers.) Herter. The plant material was collected on the Mariscal beach, Bombinhas, Santa Catarina. Fertile branches were herborized and incorporated into the Herbarium Uberlandense (HUFU). Inflorescences at various stages of development were fixed at FAA 50 for 48 hours and stored in 50% ethanol. Their flowers and buds were embedded in histological resin and serially sectioned in longitudinal and transverse planes with about 6 μm. The slides were stained with toluidine blue and mounted using synthetic resin. Acicarpha bonariensis flowers have 4–5 stamens with tetrasporangiate anthers. The anther wall development is of the Dicotyledonous-type, with the persistent epidermis, fibrous endothecium, an ephemeral middle layer, and uniseriate and secretory tapetum with cells with a polyploid nucleus. The pollen grains are formed by meiosis of microsporocytes with simultaneous cytokinesis, forming tetrahedral tetrads of microspores. These originate psilate, tricolporate and bi-celled pollen grains, which are exposed by anthers longitudinal lateral openings. After leaving the anthers, the pollen is presented secondarily by protrusion of the style. The ovary is inferior with a single, anatropous, unitegmic, and tenuinucellate ovule with apical placentation. The megagametophyte is of the Polygonum-type, formed by megasporocyte meiosis originating a linear tetrad of megaspores. Of these, only the chalazal is functional and generating three antipodals, one binucleate central cell, one oosphere and two synergids with filiform apparatus. Our results showed that the embryology of A. bonariensis is similar to the other Asterales and is different in some aspects to the basal groups of Asteraceae. In a next analysis, we will evaluate the evolutionary meaning of our findings.