Many indigenous societies insist that their knowledge comes principally from the ancestral/spirit world, which infused the natural world, particularly the plants, and comes to them primarily through dreams or visions.

In southern Africa the use of woodland and forest species of plants for this purpose is widespread and is of fundamental importance in the training of spiritual healers (izangoma, amagqirha) amongst the Nguni speaking peoples, such as the Zulu, Xhosa, Swazi, Ndebele. They are used primarily as cleansers of mystical darkness, protectors against negative and evil forces, and as connectors to the spirit world. The use of such plants is essential in the training of a healer and the inability to access certain species may severely impede their progress.

The primary aim of training among Zulu spiritual healers is to enhance awareness of the various forms of communication received from the spirit world. Dreams are of particular importance and a variety of plants species are imbibed to enhance the clarity and reception of powerful message dreams. These are collectively referred to as ubulawu and include trees, shrubs, climbers and small flowering plants from a variety of habitats.

Different parts of the plant (roots, stems, bark, bulbs and leaves) are used depending on the species. They are combined into specific mixtures, depending on the individual's progress and the nature of his/her dreams. A mixture or combination of ubulawu species is used at the commencement of training, during the training process and after a healer has qualified. They are often administered during group rituals, or may be taken daily by the novices. Certain species of ubulawu are also associated with different clans and are used as a form of identity during collective clan rituals.

The efficacy of ubulawu is largely dependant on the ritual and cultural context in which it is used. The ubulawu are soaked in cold water and beaten into a thick white foam with a forked stick (again made from a particular plant species), which is then imbibed. The ritual is often performed in pools, rivers or forests where the spirits are thought to reside, and with the accompaniment of singing and dancing. The foam is regarded as having a special cleansing ability, in both a physical and a spiritual sense. The ubulawu are also said to clean the ancestors. The power of the healer is ultimately dependent on the power of the ancestors, and by `cleaning' with ubulawu, the ancestors are `strengthened', thus enabling the healer to do his or her tasks more effectively.

Ubulawu species are classified into three groups determined by the type of ancestor or spirit that is being cleansed. These are based on the gender categories, both individually and in combination. Ubulawu species used for cleaning and connecting with the male ancestors are called mndiki, those for the female ancestors, mndawu, while idlozi is used for the combination of male and female ancestors who have been incorporated into the benevolent ancestral body through the ukumbuyisa ritual.

Mndiki species are typically reddish in color, while the idlozi mixtures are often classified as white. The Xhosa have a similar system of color classification. Black, red and white are important symbolic vehicles in Nguni cosmologies (Ngubane 1977). The use of such plants without spiritual calling and sanction renders them ineffective and izangoma are insistent that if a person has done wrong and offended the ancestors the ubulawu will not foam despite vigorous beating.

A diverse array of wild plant species found in specific habitats are thus of fundamental importance in regulating social and spiritual relationships and are integral to many of the cultural healing traditions of southern Africa. These cultural and spiritual `values' are intimately linked with worldview and indigenous knowledge.