A primordium in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow. In flowering plants, a floral primordium gives rise to a flower.
Root primordia (brown spots) as seen on the butt of a freshly cut pineapple crown intended for vegetative reproduction.
In cell biology, the meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until they become differentiated and lose the ability to divide.
Note the long spur of the above flower. Spurs attract pollinators and confer pollinator specificity. (Flower: Linaria dalmatica)
Complex leaves of Cardamine hirsuta result from KNOX gene expression