The primary inflorescence architecture and the dynamic of the floral stem development have been studied in 4 ecotypes of Arabidopsis. Clear differences have been found between ecotypes. Lansberg erecta (Ler) ecotype has a short inflorescence and a progressive decreasing in the internode length train. The three other ecotypes showed an organization with successive alternation of long and short internodes. At the level of the internode, floral stem growth dynamic showed on! y a weil synchronization with light and dark alternation with Ler ecotype. Moreover, circadian oscillations in growth rate were observable with Ler and Columbia (Col) ecotypes but not with C24 or Wassilewskija (Ws).