The Disappearing Flora:

Botanists estimate that there are some 25,000 species currently threatened with extinction. Africa's Cape region contains one of the six most significant concentrations of flora on Earth, including 68% of South Africa's 2,373 endangered plants. Modern plant breeding has emphasized inbred, uniform strains. Plant diseases and pest infestations can devastate modern breeds. Only four varieties produce 75% of the wheat grown on Canada's prairie land. Half of this land is covered by just one variety, Neepawa.