THE MORPHOLOGY OF THE EXINE IN NIGELLA (RANUNCULACEAE)

The pollen morphology of eight species of Nigella (Ranunculaceae) was examined by scanning and transmission electron microscopy. The exomorphology of all species was identical: 3-colpate, spinulose, and punctate, but thin sections revealed two structural patterns. The ektexine structure of Nigella integrifolia, consisting of thickened foot layer, columellae, and thin tectum, is typical for the family as well as the order Ranunculales in general. In contrast, the remaining seven species, N. arvensis, N. damascena, N. elata, N. hispanica, N. sativa, N. segetalis, and N. stellaris, have an ektexine with an additional unit, a horizontal layer with shorter columellae, placed between the foot layer and tectum. Of all genera examined in the Ranunculaceae, only Nigella had this unusual stratification. This difference in the exine structure would add support to the treatment of N. integrifolia as a monotypic genus, Komaroffia integrifolia (Regel) Lemos Pereira.