Danish botanist, surveyor and colonial administrator who collected plants in the West Indies and studied the cultivation of cotton. Born into a Prussian family, Julius von Rohr studied medicine at Halle University, emigrating to Denmark at the beginning of the Seven Years War (1756). In 1757 he was appointed government land surveyor in the Danish West Indies (present-day Virgin Islands) and was tasked with making a study of the islands' natural history. He happily carried out this investigation, botany being his particular passion. While in the Caribbean he began corresponding with noted naturalists in Europe and established a botanic garden on the island of St. Croix.
Promoted to the position of Lieutenant Colonel, Rohr began studying the cultivation of cotton in the Antilles, travelling around the West Indies and to the Caribbean coast of South America, collecting plants and pursuing his cotton studies. One of the first trips he made was in 1784, when he collected flowers of the introduced spice, nutmeg (Myristica fragrans Houtt.) on the Isle de Cayenne off the coast of French Guiana. These are the first preserved specimens of nutmeg grown in the Americas, now in the herbarium of the Natural History Museum in London (BM).
In 1786 he collected in Puerto Rico and other Caribbean islands, sending seeds and plants to Professor Martin Vahl in Copenhagen for determination. Rohr described eight new genera himself, including the Bidens L. relative, Melanthera Rohr, and is commemorated in the monotypic genus Rohria Schreb. His observations on the cottons of the West Indies provide the main source of information about the crop in the 18th century and were used by C.S. Rafinesque as the basis for naming 38 species and varieties of Gossypium. Two species of cotton are named in honour of Rohr: G. rohrianum Raf. and G. rohrii Tod.
Rohr's West Indian collecting days came to and end in 1791, at a time when Denmark was looking into establishing plantations in Danish lands in West Africa (the days of the Atlantic slave trade coming to an end). With his experience in colonial administration and scientific knowledge, Rohr was chosen as the ideal candidate to judge the feasibility of such an enterprise and was thus sent via the United States to Guinea. Rohr's report on Guinea's agricultural potential was never submitted, however; the ship was lost on the Atlantic.
Sources:
P.A. Fryxell, 1969, "The West Indian Species of Gossypium of von Rohr and Rafinesque", Taxon, 18(4): 400
T.J. Zumbroich, 2005, "The introduction of nutmeg (Myristica fragrans Houtt.) and cinnamon (Cinnamomum verum J.Presl) to America", Acta Botanica Venezuela, 28(1): 155-160.
