Thailand’s natural vegetation includes a wide range of forest types. In the south, tropical semievergreen rain forests are most common. In the north, two types of forests grow: monsoon forests, characterized by dense-growing, broadleaf deciduous trees, and savanna forests, in which grasses and sedges (grasslike flowering plants with triangular stems) grow beneath open stands of widely spaced trees. During the dry season, in both the monsoon and savanna forests, the trees shed their leaves and fires can occur. The monsoon forests are particularly noted for their useful species of trees and plants, including teak, which is highly valued for its strength and durability, and many types of bamboo. The forests abound in orchids, which are widely collected and grown in gardens.