Palynological analysis of representatives of Hippeastrum Herb. (Amaryllidaceae: Amaryllidoideae), with implications for systematics

Native to the American continent, the genus Hippeastrum Herb. is distributed from Mexico to Argentina. In Brazil, it is represented by approximately 30 species. This study examined the pollen grains of 20 taxa within the genus to determine whether differences in pollen morphology could support a clearer delimitation and characterization of subgenera and subordinate species. Pollen grains were treated with 40% lactic acid, measured, described, and photomicrographed. Non-acetolyzed pollen grains were examined using scanning electron microscopy. The analyzed taxa have large to very large pollen grains, shed as monads, monosulcate, with an elliptical shape in polar view and a reticulate or retipilate sexine. Species with a retipilate sexine could be distinguished based on the characteristics and organization of pila, whereas those with a reticulate sexine could be differentiated by murus, lumen, and columella characters. Thus, it was possible to develop a palynological key. Qualitative and quantitative analyses revealed differences in pollen morphology among species. However, pollen characters were generally uniform among subgenera. Overall, pollen characters proved informative for delimiting and describing species within the genus Hippeastrum .