Abstract: The evolutionary relationships of genera in Papaveraceae are particularly controversial. The structures and developments of seedlings in 4 species of 3 genera were studied with the methods of tissue cleaning and paraffin section in this paper. Representatives of genus Papaver are Papaver rhoeas and Papaver orientale, while Chelidonium majus and Corydalis bungeana are representatives of genera Chelidonium and Corydalis, respectively. The results indicate the haplostele types are different in the lower part of cotyledon node zone (CNZ) of three genera. Genera Papaver and Chelidonium are exarch diarch rotundity haplostele and rotundity-like haplostele, respectively, and genus Corydalis is exarch diarch “S”-shape haplostele. And the cotyledon venations of three genera seedlings are distinct. Papaver rhoeas and Papaver orientale have only a single primary vein, and no leaf gaps existed on the cotyledon node. Chelidonium majus and Corydalis bungeana have Brochidodromous-Camptodromous-Pinnate venation and Basal-Perfect-Acrodromous venation, respectively. In terms of the evidence from the structures of primary vascular system of seedlings, the evolvement levels of three genera are that Papaver is more primitive, followed by Chelidonium, and Corydalis is the most developed.

Key words: Papaveraceae, seedling, primary vascular system, structure