Complex sentence: A cultigen is a plant that has been deliberately altered or selected by humans; it is man-made (human-altered) or anthropogenic and are derived and used almost exclusively within horticulture, agriculture and forestry.
Split into simpler sentences: A cultigen is a plant that has been deliberately altered or selected by humans; it is man-made (human-altered) or anthropogenic. Anthropogenic plants are derived and used almost exclusively within horticulture, agriculture and forestry.