The ultrastructure and lipid composition of chloroplasts, isolated from various shade and sun plants, were compared. Depending on the origin of the plastid, significant differences were observed in the percentage of appressed thylakoids. Accordingly, plastids could be classified into three different types: Type I chloroplasts, from mesophyll cells of sun plants (barley, corn, spinach, bean), display well-developed grana and intergrana thylakoid membranes. Type II chloroplasts, typical of shade plant (Arum), show giant grana stacks with few interconnecting thylakoids. Type III chloroplasts, from bundle sheath cells of leaves from C4-plants (corn), are characterized by an extensive development of stroma thylakoids with only occasional rudimentary grana. The percentages of appressed membranes are in the ranges of 50 to 60%, 80% and 2% for type I, II and III plastids respectively. Striking differences are observed in the fatty acid composition of phosphatidylglycerol molecules. Trans-delta3-hexadecenoic acid is found only in this phospholipid and amounts to 30 to 40%, 50% and less than 8% of total fatty acids in type I, II and III plastids respectively. The comparison of ultrastructural and biochemical data suggests a strong correlation between the amounts of phosphatidylglycerol molecules containing trans-delta3-hexadecenoic acid and the percentages of appressed membranes (grana stacks) within plastid stroma.