The development of inflorescence, flower and pollen in Tajetes patula (Asteraceae): flower structural traits in plant-pollinator relationships

Flower development is a mystery and provides a useful means for understanding cell differentiation and genetic mechanisms needed for organogenesis. Tajetes patula is an annual herbaceous ornamental species belonging to the family Asteraceae. In this study، the structure and development of inflorescence، flower and pollen grains and their characteristics related to pollination were assayed. The inflorescence was capitulum in which involucral bracts primordia were subtend inflorescence meristem and then floret primordial was initiated centripetally on flatten generative meristem. A dimple appeared on the top of floret primordium، and a corolla was produced first. Inside the developing corolla 5 staminata primordial and two-lobed pistillata primordium arise. Five staminata primordia surrounded the pistillata primordium. Gynomonoecious inflorescenc consisted of high number of fertile bisexual tubular florets and sterile female ray florets. Both florets consisted of small bract like sepals، inferior ovary، bifid stigmas containing numerous papillate cells and single styles which were of the closed type with a filled stylar canal. The anthers were synatherous; tapetal layer was of secretory type firstly but finally its cells enter the anther locule and was converted to amoeboideus type. The endothecium was fibrous and anther dehiscence was longitudinal and extrose. Cytokinesis was simultaneous and mature pollen grains were yellowish، 31 um in diameter، triapertures (tricolporate) and echinate with small pores in base. Fruit was elongated and black achen. Traits such as the formation of capitulum inflorescence، its color، secretory (papillate) epidermis on the adaxial surface of petals، color and sculpture (echinate) of pollen grains، grown and bifid stigmata attract insects as pollinators and improves pollination.