The approximately 270,000 known species of plants form the basis of all food chains on earth and fuel all life systems (although even this number is only a fraction of plant diversity). From this fact alone, plants should be an important part of biodiversity conservation. An overview is provided of plant classification and systematics as well as the diversity of plant physiology and ecology. Plants can also be very valuable to humans for reasons illuminated by the fields of ethnobotany (focusing on traditional uses and medicinal plants) and economic botany (looking at plant properties for novel commercial uses). Unfortunately, like animals, plants are also facing serious threats in terms of illegal trade and invasive species that need to be brought under control.