South African botanist. His family emigrated from Germany when he was a small child, and lived in Tanzania and Zimbabwe before settling permanently in South Africa. After graduating from the University of Stellenbosch, he joined the Botanical Research Institute in Pretoria in 1955. He was stationed for six years (1957-1963) at the McGregor Museum in Kimberley and served for two years (1965-1967) as Liaison Officer at Kew. Between these postings he received a doctorate from Stellenbosch for his thesis on the plant ecology of the southern Kalahari. He returned to Pretoria to lead the Herbarium Services (1967-1976) and later the Floral Research Section (1976-1985) where he was instrumental in introducing the Degree Square System for citing biological records in southern Africa and in developing PRECIS (National Herbarium of South Africa [PRE] Computerised Information System). From 1985 until his retirement in 1996, he was Head of Publications and scientific editor of Bothalia, Flora of Southern Africa, Memoirs of the Botanical Survey of South Africa and later Strelitzia. Between 1991 and 1997, he was also editor of Flowering Plants of Africa. His major publications include The Plant Ecology of the Southern Kalahari (1967), Southern African Place Names (1976, co-authored with J.W. Morris), and Seed Plants of Southern Tropical Africa: Families and Genera (2005).

The bulk of this collections were made in poorly to very poorly known areas: in Kaokoveld, Namibia, with Bernard De Winter in March-May 1957; in eastern Caprivi Strip, Namibia, with D.J.B. Killick in Dec 1958-Jan 1959; and in the Northern Cape, particularly the Kalahari, between 1957 and 1963. Androcymbium leistneri U. Müll.-Doblies & D. Müll.-Doblies, Dicliptera leistneri K. Balkwill and Euphorbia leistneri R.H. Archer are named after him.