Concept:Placentation type is determined by the number and fusion of carpels forming the ovary.
Explanation:A syncarpous pistil is one in which two or more carpels are fused together to form a compound ovary.
Axile, parietal, and free central placentation are commonly observed in such syncarpous pistils.
Marginal placentation, however, occurs along the single margin of a solitary carpel.
Hence, it is characteristic of a simple or monocarpellary pistil, not of a syncarpous pistil.
So, among the options given, marginal placentation is the one that is not common in syncarpous pistils.
Answer:A. Marginal