Jacques Denys (Denis) Choisy (5 April 1799, Jussy – 26 November 1859, Geneva) was a Swiss Protestant clergyman and botanist.^[1]

He studied theology, law, humanities and sciences at the Académie de Genève. In 1821 he became ordained as a minister, and during the following year, furthered his education in Paris. During his stay in Paris, he was accepted as a member of the Société d'histoire naturelle. Following his return to Geneva in 1824, he was named chair of rational philosophy at the Academy, a position he maintained until 1847.^[2]

As a student in Geneva, he came under the influence of Augustin Pyramus de Candolle, and in the process, developed a lifelong passion for botany.^[2] He was a principal contributor towards Candolle's publication of "Prodromus Systematis Naturalis Regni Vegetabilis", being the author of the sections involving the plant families Marcgraviaceae, Convolvulaceae, Hydroleaceae, Selaginaceae, Nyctaginaceae, Hypericineae and Guttiferae.^[3] The botanical genus Choisya (family Rutaceae) is named in his honor.^[4]

As a theologian/philosopher he published works with titles such as, "Des doctrines exclusives en philosophie rationelle" (1828) and "Les lois morales: Fragment d'un cours de philosophie morale" (1836).^[5]

Selected botanical works

• Prodromus d'une monographie de la famille des hypéricinées, (9 editions issued from 1821 to 1983) – Prodomus of a monograph on Hypericineae.
• Descriptions des Hydroléacées, 1830 – Descriptions of Hydroleaceae.
• Convolvulaceae orientales, 1834 – Convolvulaceae Oriental
• Mémoire sur les familles des Ternstroemiacées et Camelliacées, 1854 – Treatise on the families Ternstroemiaceae and Camelliaceae.^[6]