Root nodules are specialized structures found in certain plants that have a mutualistic relationship with nitrogen-fixing bacteria. These bacteria, called rhizobia, form a symbiotic relationship with the plant roots. The plant provides the bacteria with carbohydrates, while the bacteria fix atmospheric nitrogen into a form that the plant can use.

Option 1: Parasitic plants obtain their nutrients from other plants, therefore, they do not have root nodules.

Option 2: Epiphytic plants grow on the surface of other plants and derive nutrients from the air and rainwater. They do not have root nodules.

Option 3: Leguminous plants, such as peas, beans, clover, and soybeans, commonly have root nodules. These nodules contain the nitrogen-fixing bacteria and help the plant convert atmospheric nitrogen into usable nitrogen compounds.

Option 4: Aquatic plants do not typically form root nodules as they obtain nutrients from the water in their environment.

Therefore, the correct answer is option 3 - Leguminous plants.