The term 'Water Clover and Adder's-Tongue' is a collective name for two types of ferns, Marsilea quadrifolia (Water Clover) and Ophioglossum vulgatum (Adder's-Tongue). These ferns are found in many parts of the world, including North America, Europe, and Asia. They are both aquatic plants, meaning they grow in or near water, and they have a unique four-leaf clover shape. Water Clover is a small, low-growing plant with round leaves, while Adder's-Tongue has long, thin leaves that resemble a snake's tongue. Both species are important components of wetland ecosystems, providing food and shelter for wildlife.