Spanish pharmacist and member of the Botanical Expedition to New Spain. Juan Diego del Castillo was born in Jaca, Aragon, and studied Latin and pharmacy. In 1771 he moved to Puerto Rico to become a pharmacist (Boticario Mayor) at the Royal Hospital, from which he corresponded with the Botanic Gardens of Madrid. In 1788 he was chosen by the director of these gardens, Casimiro Gómez Ortiga, to travel to Mexico and join the botanical expedition as a botanist and to aid the director, Martín Sessé, in his plant collecting excursions.

Along with Jaime Senseve he collected specimens that his companion on the expedition, Vincente Cervantes, organised in the newly created botanical gardens in Mexico City. From the beginning Castillo suffered from health problems which Sessé described as scurvy while Cervantes believed he had an obstruction in the pylorus of the stomach. Unfortunately his illness was fatal and Castillo died early on in the expedition (at the age of just 49) in the region of Tarahumara in the Sierra Madre Occidental, having over exerted himself on the excursions. The Mexican naturalist José Mariano Moçiño took his place and would become a very important character in the expedition.

In his will Castillo left 4,000 pesos for the printing and engraving of the Flora Mexicana which the botanists of the expedition were ultimately working to produce. Unfortunately when his companions returned to Spain in 1803 the Napoleonic wars made it extremely difficult for them to gain sufficient funds and the flora remained unpublished until the end of the century. Castillo did, however, publish a description of the plants from the journey to Acapulco and the genus Castilloa was named after him by Cervantes, who worked extensively on the Panama rubber tree Castilloa elastica.

Sources:
Colmiero, M., 1858, La Botánica y Los Botánicos de la Península Hispano-Lusitana. Imprenta y Estereotipia de M. Rivadeneyra. Madrid.
García Montoya, F., 2003, Botánicos de los Siglos XVI, XVII y XVIII. Cabra. Córdoba.
Ricket, H. W., 1949, The Royal Botanical Expedition to New Spain. The Cronica Botanica Co. Waltham, Massachusetts, U.S.A.
San Pío Alardeen, M. P. and Puig-Samper Mulero, M. Á, Eds., 1999, Las Flores del Paraíso: La Expedición Botánica de Cuba en los Siglos XVIII y XIX. Real Jardín Botánico, Madrid.
Archives:

Archivos Real Jaraín Botánico Madrid. Letter from Vicente Cervantes to José Celestino Mutis. Dated 17th March 1788. III.1.1.82.