زهره شیرخانی - Assistant Prof., Department of Plant Sciences, Faculty of Biological Sciences, Kharazmi University, ۱۵۷۱۹-۱۴۹۱۱, Tehran, Iran
عبدالکریم چهرگانی راد - Prof., Department of Biology, Bu-Ali Sina University, Hamedan, Iran
فریبا محسن زاده - Associate Prof., Department of Biology, Bu-Ali Sina University, Hamedan, Iran

Artemisia annua L. (Asteraceae) is a species with high medicinal potential. This study aimed to determine the embryological characteristics of the A. annua with a focus on the development of pollen grains and ovules to help the taxonomic position of this species. Capitulum were studied using light and scanning electron microscopies to describe the floral development. According to the results, the formation of the anther wall was dicotyledonous type and the tapetum layer was multi-nucleated and secretory. The tetrad of microspores were tetragonal and tetrahedral, and mature pollen grains were two-celled, tricolpate. The ovule was of anatropous, unitegmic, and tenuinucellate type. The archesporium was unicellular. T-shaped and linear tetrads of megaspore were observed in megasporogenesis. The micropylar megaspore developed into an eight-nucleate embryo sac with a Polygonum type pattern. Fertilization was of the porogamous type. This species displayed cellular and scant endosperm development. Some embryological features of Asteraceae, Calyceraceae, and G. oodeniaceae are also brought in the present paper. Comparisons revealed embryological features provide obvious evidence for the segregation of these close families. Therefore, based on the study, the authors suggest that systematic studies on this genus and similar genera should not only be done on the thickening of pollen grain surface, but also on the stages of anther and pollen grain development. In addition, embryo sac studies can also reveal hidden systematic differences between different arrays.

Anther, Asteraceae, embryonic sac, ovule, pollen grain