Ovules anatomy of selected apomictic taxa from Asteraceae family

The present paper reports on our observations on the ovule structure of autonomous obligatory apomicts. We analyzed two triploid species of Taraxacum: T. udum, T. alatum and two triploid species of Chondrilla: Ch. juncea, Ch. brevirostris . The ovules of all studied species show a structure typical for the members of Asteraceae. One basal ovule develops into an inferior and unilocular ovary. The ovule is anatropous, tenuinucellate and unitegmic. Structural changes were observed in the ovule at the time of the embryo sac maturation. The innermost layer of integument develops into an endothelium surrounding the female gametophyte. Moreover, considerable modifications occurred in the integumentary cell layers adjacent to the endothelium. These cells show signs of programmed cell death and their walls begin to thicken. Histological analysis revealed that the prominent thick cell walls were rich in pectins. Layers of thick-walled cells formed a special storage tissue which, most likely, is an additional source of nutrients necessary for the proper nourishment of a female gametophyte and then of a proembryo.