The science which deals with the study of plants is known as botany.
Theophrastus is known as the father of botany. He was a scientist and a Greek philosopher who studied the plants and wrote many books on systematic and organization of tissues in plants.
Carolus Linnaeus is known as the father of modern botany.
Carolus Linnaeus was a Swedish botanist, physician, and zoologist who formalized binomial nomenclature, the modern system of naming organisms.
He is known as the "father of modern taxonomy". Hence, the father of modern botany is Linnaeus.