The correct answer is option 1: Dicot plants.

Guard cells are specialized cells found in the leaves of plants and are responsible for controlling the opening and closing of stomata, which are small openings on the surface of leaves that allow for gas exchange. The shape of the guard cells plays a crucial role in this process.

In dicot plants, which include plants like roses, sunflowers, and tomatoes, the guard cells are typically kidney-shaped. This shape allows for a larger opening when the guard cells are turgid (fully swollen with water), which facilitates the exchange of gases and the release of water vapor.

On the other hand, in monocot plants like grasses and lilies, the guard cells have a different shape, usually elongated or dumbbell-shaped. In these plants, the stomata are usually arranged in parallel lines, and the guard cells function similarly to those in dicot plants.

Therefore, the correct answer is dicot plants.