Jean-Jacques Rousseau is best known as a philosopher, if not a writer of fiction. And yet, in the last decade of his life he devoted much of his time to empirical studies of biological organisms. These studies seem to have been quite extensive. If we confine ourselves to writers who are lined up in traditional histories of philosophy, Rousseau's biological studies are probably outmatched only by those of Aristotle and Theophrastus. He made his own herbaria, and he even wrote a few botanical works: a (fragmentary) dictionary of botanical terms, and a series of “elementary” letters on botany to his “dear friend” Madame Delessert, who asked for advice on how to introduce her daughter Marguerite-Madeleine to the study of plants. These letters were written between 1771 and 1773, and published for the first time in Geneva three years after his death in 1778. The most famous edition, from 1805, included illustrations made by the most celebrated of all botanical illustrators, Pierre-Joseph Redouté, “the Raphael of flower painting,” protégé of both Marie-Antoinette and, in particular, Josephine Napoléon, who spent a significant part of her fortune on this sponsorship.

Unlike the biological studies of Aristotle and Theophrastus, which were not superseded for two millennia, there is nothing original in Rousseau's empirical studies. He followed the sexual system of Linnaeus rather slavishly, and he does not seem to have found any new species or any features of plants which were not described before.