Rarest plant

One of the world's rarest plants is Encephalartos woodii, a cycad, of which only one specimen has ever been found growing wild in the Ngoya forest of KwaZulu-Natal, South Africa, in 1895 by John Medley Wood (South Africa). This specimen has long since disappeared and others now exist only in botanic gardens. The plant's name commemorates John Medley Wood, the director of the Natal Government Herbarium, South Africa. Three of its four main stems were collected on a subsequent expedition and have been the source of all the material now grown in botanic gardens around the world. Kew received one of these stems in 1899. Offshoots from the stems sent to South African botanic gardens have since been propagated. Like all cycads, E. woodii is dioecious; that is, it bears male and female cones on different plants. As no female plants have ever been found, the seed cones are unknown.

http://www.kew.org/plants/cycads/encephalartos_woodii.html