Which of the following types of placentation is not common amongst syncarpous pistils?

Analyze the question: It asks which placentation is NOT common in syncarpous pistils. A syncarpous pistil is one where the carpels are fused together.

Concept: Placentation is the arrangement of ovules inside the ovary. The main types are:

• Marginal: Ovules are attached along the margin (edge) of a single carpel. This occurs in a monocarpous (single carpel) ovary, such as in legumes like beans and peas. It is not found in fused carpels.
• Axile: The carpels are fused, and ovules are attached to a central axis in separate chambers. It is found in hibiscus, tomato and orange. Syncarpous.
• Parietal: The carpels are fused into a single chamber, and ovules are attached to the ovary wall. It is found in pawpaw and cucumber. Syncarpous.
• Free central: The ovary has one chamber, and ovules are attached to a central column that is not connected to the walls by partitions. It is found in primrose and Dianthus. Syncarpous.

Solution:

• Axile, parietal and free central all occur in fused-carpel (syncarpous) ovaries.
• Marginal placentation belongs to a single carpel (monocarpous), so it is not common in syncarpous pistils.

Answer: **A.

Tip: Link "marginal" to "mono": one carpel, with ovules along its edge (like peas in a pod). For fused carpels, remember the three others: Axile, Parietal, Free central (the "syncarpous trio").