Embryology of Tripleurospermum disciforme: New and rare type of embryogenesis

Embryological characteristics of Tripleurospermum disciforme were studied in this research. The flowers and buds in different developmental stages were removed، fixed in FAA70، stored in 70% ethanol، embedded in paraffin and sectioned at 7-10 µm with a microtome. Staining was carried out with PAS and contrasted with Hematoxylin. Results indicated that anthers are tetrasporangiate and anther tapetum is of the secretory type. Pollen tetrads are tetrahedral and tetragonal. Pollen grains are 2-celled when shed. Ovule is anatropous، unitegumic and tenuinucellate. Endothelium is uniseriate. Embryo sac development is of the Polygonum type. Antipodal cells increase up to 6-8 and their nuclei become polyploidy. Results of this research showed that embryogenesis of Tripleurospermum disciforme should be regarded as exceptional type. There are two type of embryogenesis. In some florets، that are hermaphroditic، embryo sac was developed as Polygonum type with increasing of antipodal cells and zygotic embryogenesis are in current. But in some florets، that are also hermaphroditic، antipodal cells were increased and they are large in size with condense cytoplasm. They are long-lived and cause to form embryo without fertilization. In these cases the egg apparatus were degenerated due to underutilization of oospher.