What is the name of the green substance that grows in wet places?

The green substance that typically grows in wet places is known as algae. Algae are photosynthetic organisms found in a variety of aquatic and moist environments, including ponds, lakes, and damp surfaces. They can range from single-celled organisms to large multicellular forms like seaweeds, and they play a crucial role in producing oxygen and serving as a food source in ecosystems.

Mould, on the other hand, refers to a type of fungus that typically thrives in humid conditions but is not characterized by a green color specifically, nor does it primarily inhabit wet environments in the same way algae do. Lichen, a symbiotic relationship between algae and fungi, often grows in moist locations but is not itself solely the green substance; it includes both components. Fungi encompass a broad category of organisms, including mushrooms and mould, but do not specifically denote the green growth commonly seen in moist areas. Thus, algae is the correct identification of the green substance in question.