Coriander roots

Exposed roots

The aerial root of a young Pōhutukawa tree (Metrosideros excelsa), Mount Wellington, Auckland, New Zealand

Mangroves in West Bali National Park, Indonesia. Notice the aerial roots

The roots of a plant is the part that is usually buried in the soil. Roots are usually always under the soil, though–sometimes roots can be above the ground. This is called an aerial root.

Also, stems can sometimes be under the soil (potatoes, for example). Roots do not have leaves, and are different from stems inside.