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Abstract
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Flower development is a mystery and provides a useful means for understanding cell differentiation and genetic mechanisms needed for organogenesis. For this purpose, in this research, the structure and developmental stages of inflorescence and pollen grains were studied in Artemisia aucheri. A. aucheri is an herbaceous species belonging to the family Asteraceae. The flower and buds in different developmental stages were removed, fixed in FAA, stored in70% ethanol, embedded in paraffin and sliced with a microtome. Results showed that transition of vegetative meristem to generative one is observed as increasing of the dimension of meristem and its dyeability. The inflorescence is of capitulum type in which involucral bracts were developed and then floret primordial were initiated centripetally on flatten generative meristem . Each primordium causes to form a floret with its segmentation. Each inflorescence contained some peripherally located sterile radial florets and a large number of central fertile liguliform florets. Both florets consisted of small bracts like sepals, inferior ovary, anatropous ovule, bitegumic and tenuinucellate ovules. Embryo sac development was of the Polygonum type. Antipodal cells increased up to 6- 8that is an exceptional character for this species. Anthers are tetrasporangiated and development of anther wall is of dicotyledonous type and composed of the one-layered epidermis, an endothecium, one middle layer and tapetum. Tapetal cells showed high polyploidy level that is necessary for its function. Tapetum is of the secretory type at the beginning and plasmodial type at the final stages of development.The endothecium was fibrous and anther dehiscence was longitudinal and extrose. Microspore tetrads are tetrahedral, in the main, and tetragonal or linear in some cases. Pollen grains are triapertures (tricolporate). Traits such as the formation of capitulum inflorescence, its color, and secretory (papillate) epidermis on the adaxial surface of
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