The huge biodiversity that Namibia offers can be divided into six main categories: Grasses, shrubs, herbs, bulbs, succulents and trees. Since Namibia is an extremely arid land, most of its vegetation is well adapted to dry spells and even longer droughts. These adaptations show in various ways. Some like the camel thorn tree have long taproots that grow deep down into the earth in search of ground water, others like the succulent plants - mostly found in the south - store water in their stems and leaves. During the rainy season Namibia is covered with annual herbs which shed their seed in wait for the next rain. The grasses that are found all over the country are very important for animals and humans, as the natural ones feed most of the livestock and the cultivated ones are staple food for man. When Namibia has had a prosperous rainy season, the central parts and quite far up North can often be found blooming with wild lilies growing out of bulbs. Namibia's plant world offers an abundance in natural, healing plants to those that have lived in the bush all their lives, like the San bushmen. However, to the untrained person it can be fatal, as euphorbias like the commonly known milk bush, and other plants are extremely poisonous and can cause rashes on the skin when touched. In severe cases, exposure can even lead to death when ingested (using sticks for toasting marshmallows) or burned and inhaled when used for making fire.