Which naturalist and artist chronicled the flora and fauna of the Louisiana Purchase?

The correct answer is rooted in the legacy of John James Audubon, a prominent naturalist and artist known for his detailed studies and illustrations of North American birds, plants, and animals. Audubon spent a significant portion of his life in the region that encompasses the Louisiana Purchase, which gave him access to a rich array of flora and fauna that he meticulously documented in his works.

His book, "The Birds of America," features a collection of hand-painted illustrations that reflect the biodiversity of the area, capturing the natural beauty and complexity of the ecosystems within the Louisiana Purchase. Audubon's work has had a lasting impact on both art and science, making him an emblematic figure of the natural history of this region.

The other choices do not pertain to notable figures or significant works related to the Louisiana Purchase and its natural history. Thus, the significance of Audubon’s contributions stands out clearly, making it the correct answer.