ABSTRACT
The diversity of wild plants is ideally preserved by allowing them to grow in their natural undisturbed habitats (Figure 17.1), where the often considerable range of genic variation can continue to exist. Unfortunately, human domination of the planet is degrading or exterminating habitats that support wild species. In some cases, wild areas are reserved to allow the organisms to continue to survive. Alternatively, selected individuals of species that are highly threatened with extinction are sometimes cared for by people in nonnatural circumstances (parks, arboreta, institutional gardens, zoos, and the like). Preservation in natural habitats has come to be categorized as in situ conservation, preservation outside of such habitats as ex situ conservation. In situ conservation is usually far less costly and is capable of maintaining much more genic diversity than is possible with ex situ conservation, which necessarily is based only on selected samples. The normally small samples of material kept in collections are subject to mutations and accidental hybridization during periodic replication and loss of alleles of genes that occurs naturally when reproduction occurs in small populations, so over time ex situ collections tend to become less representative of the original wild population. For flowering plants such as Cannabis sativa, both in situ and ex situ conservations are important, as discussed further in this chapter.
