Explore lungs of Earth: 5 largest rainforests in the world

Rainforests are often called the "world's largest pharmacy" because a quarter of natural medicines have been discovered within them.

The world's largest rainforest, the Amazon, spans 2.3 million square miles across nine South American countries.

The second largest, the Congo Basin rainforest in Central Africa, covers 780,000 square miles.

This rainforest spans six countries: Cameroon, Equatorial Guinea, Gabon, Central African Republic, Republic of Congo, and the Democratic Republic of Congo.

The world's third-largest rainforest is on the island of New Guinea.

The eastern half is part of Papua New Guinea, and the western half belongs to Indonesia. The island covers approximately 303,000 square miles.

The Sundaland rainforest, encompassing the Malay Peninsula and the islands of Sumatra, Java, and Borneo in Southeast Asia, covers 197,000 square miles.

The fifth largest rainforest is the Mekong River Basin, along the Mekong River, the longest river in Southeast Asia, at about 3,000 miles (4,900 km).