The spiritually curative medicines prescribed by a traditional healer are called "muti". They may be employed in healing as warranted in the opinion of the herbal specialist or inyanga. Muti is a term derived from a Zulu word for tree. African traditional medicine makes extensive use of botanical products but the medicine prescribed by an inyanga may also include other formulations which are zoological or mineral in composition. Traditional medicine uses approximately 3,000 out of 30,000 species of higher plants of Southern Africa. Over 300 species of plants have been identified as having psychoactive healing effects on the nervous system, many of which need further cultural and scientific study In South African English and Afrikaans, the word muti is sometimes used as a slang term for medicine in general.