Plants that show secondary growth are usually found among the

1. Analyze the question The question asks which group of plants usually shows secondary growth, which is growth in girth (thickness).

2. Explain the concept

• Primary growth is growth in length, produced by apical meristems at the shoot and root tips.
• Secondary growth is growth in thickness. It comes from lateral meristems: the vascular cambium and the cork cambium. The vascular cambium produces secondary xylem (wood) and secondary phloem, and the cork cambium produces bark.
• This needs a cambium between the xylem and phloem in a ring of open vascular bundles.

3. Solution: checking each option

• A. Thallophytes (algae and fungi): They have no true roots, stems, leaves or vascular tissue, so there is no cambium and no secondary growth.
• B. Pteridophytes (ferns): They have vascular tissue but no vascular cambium, so they do not show secondary growth.
• C. Monocotyledons (e.g., maize, grasses, palms): Their vascular bundles are scattered and closed, meaning there is no cambium. They generally lack secondary growth. This is why a maize stalk does not get thicker year after year.
• D. Dicotyledons (e.g., mango, orange, hibiscus, cashew): Their vascular bundles are arranged in a ring and are open, with a cambium between the xylem and phloem. They therefore show secondary growth, which gives woody trees and growth rings.

4. Answer The correct option is D. dicotyledons.

5. Exam tip Remember: "Dicots have Cambium, so they get Chunky." Dicot means open bundles, which means cambium, which means secondary growth. Monocot means scattered closed bundles, which means no cambium, which means no secondary growth. A few exceptions exist, such as palms and some monocots with unusual thickening, but JAMB expects "dicotyledons" for this type of question.