An example of a monocot plant having secondary growth is :

Question

Accepted Answer

The correct option is 3: Dracaena

Secondary growth is the process that increases the girth or thickness of a plant stem or root, primarily due to the activity of lateral meristems, namely the vascular cambium and cork cambium. As a general rule in plant anatomy, this type of growth is a characteristic feature of dicotyledonous plants and gymnosperms, and is typically absent in monocotyledonous plants. The question asks for a rare exception to this rule, and the correct answer is indeed Dracaena (such as the Dragon Tree), which is a monocot. Dracaena exhibits a special form of thickening known as "anomalous secondary growth." In this specific monocot, a type of cambium, referred to as an accessory cambium, develops in the ground tissue outside the primary vascular bundles. Unlike the typical dicot cambium that produces secondary xylem (wood) to the inside and secondary phloem to the outside, the *Dracaena* cambium produces new vascular bundles and parenchyma tissue towards the inside and parenchyma tissue to the outside. This unique pattern of cell division and tissue production is what allows the *Dracaena* stem to increase significantly in diameter, giving it a woody, tree-like appearance, even though it does not produce true, dense secondary wood.

The incorrect option is 1: Bignonia

Bignonia is an incorrect choice because it is fundamentally a dicotyledonous plant, belonging to the family Bignoniaceae, which is a large group of Eudicots. Since secondary growth is the standard form of thickening in dicots, Bignonia's presence of secondary growth is a typical dicot characteristic, not an exception to the monocot rule. *Bignonia* is often a liana (a woody climber) and does exhibit an *anomalous* type of secondary growth that is adaptive for its climbing habit, specifically forming phloem wedges in the xylem region. However, this anomaly is observed within the dicot class, and thus it cannot be the monocot example required by the question. Its classification as a dicot makes it instantly incorrect.

The incorrect option is 2: Nyctanthes

Nyctanthes is incorrect because it is also a dicotyledonous plant, not a monocot. Commonly known as Night Jasmine or Harsinghar, *Nyctanthes arbor-tristis* belongs to the family Oleaceae, the Olive family, which is firmly classified under the Eudicots. As a woody shrub or small tree, it undergoes normal, typical secondary growth characteristic of dicots, where the vascular cambium produces secondary xylem and secondary phloem. Its growth pattern adheres to the conventional dicot anatomy, lacking the exceptional, anomalous secondary growth required to be an answer to the question about monocots. Its classification as a dicot immediately disqualifies it from the correct category.

The incorrect option is 4: Leptadenia

Leptadenia is an incorrect option as it belongs to the family Apocynaceae (the dogbane family), which is a member of the Angiosperm Eudicots. The plant is typically a twining shrub or vine. Like all dicots, it possesses the genetic program and meristematic tissues to undergo standard secondary growth to increase its girth and become woody. The presence of secondary growth in *Leptadenia* is therefore an expected feature of its dicot anatomy, not the rare exception found in the monocot group. The focus of the question is to identify a monocot that breaks the general rule, and *Leptadenia*, being a dicot, is automatically ruled out.