The book Systema Naturae was written by (a) Linnaeus.
Explanation: Carolus Linnaeus, a Swedish botanist and zoologist, is credited with writing Systema Naturae, where he introduced his binomial system of classification.
Key points about the other options:
Haeckel: Ernst Haeckel was a German biologist who proposed a three-kingdom classification system.
Whittaker: Robert Whittaker developed a five-kingdom classification system.
Robert Brown: Robert Brown was a British botanist who discovered the nucleus within plant cells.