weeds
We obviously cant live without plants, but sometimes they cause us problems. Many plants are weeds. Weeds are plants that grow where people dont want them, such as gardens and lawns. They take up space and use resources, hindering the growth of more desirable plants. People often introduce plants to new habitats where they lack natural predators and parasites. The introduced plants may spread rapidly and drive out native plants. Many plants produce pollen, which can cause allergies. Plants may also produce toxins that harm human health see Figure below .