Flora refers to the plant life occurring in a particular region. Plants are grouped into floras based on region, period, special environment, or climate. Regions can be geographically distinct habitats like mountain vs. flatland, desert vs. wetland. Plants are one of Earth's greatest resources. They are sources of food, medicines and materials with vast economic and cultural importance. They stabilize ecosystems and form the habitats that sustain the planet's animal life. There are estimated 400,000 species of vascular plants on Earth, with some 10% more yet to be discovered.