Otto W. Sonder, German pharmacist and botanist, completed a four-year apprenticeship as a pharmacist in Hamburg in 1832. During his appreniticeship he actively collected plants and acquired an extensive knowledge of botany. After further training in southern Germany he passed the state examination in pharmacy in Berlin in 1835. Around that time he published his first botanical paper, dealing with the genus Salix (willows). He was first employed in Kiel and subsequently in Eimbeke's pharmacy in Hamburg, which he later owned. During these years he visited the Alps and the Mediterranean countries to collect plants, but his botanising was later confined to the neighbourhood of Hamburg, where he remained for the rest of his life. In 1844/5, he described new species of Algae collected in Australia by J.A. Ludwig Preiss* in the Botanische Zeitung, and is said to have obtained a nearly complete set of the latter's plants, including those collected at the Cape. In 1851 he published Flora Hamburgensis (Hamburg, 601p), on which he had worked for 20 years and which showed him to be an experienced and meticulous botanist. Later he returned to the study of Australian algae with an extensive paper in the Abhandlungen aus dem Gebiete der Naturwissenschaften (Hamburg, 1871).
Although he never collected in southern Africa, Sonder is well known for his publications on South African botany. He wrote a revision of the local genus Heliophila (Family Cruciferae) in the Abhandlungen des Naturwissenschaftlichen Vereins (Hamburg, 1846, 103p), based on the collections of Cape plants by J.F. Drège*, C.F. Ecklon* and C.L.P. Zeyher* ; an enumeration of the orchids collected in South Africa by Ecklon and Zeyher (Linnaea, 1847, 42p); "Beiträge zur Flora von Südafrika" (Contribution to the flora of South Africa; Linnaea, 1850, 138p), which contained descriptions of many new species; and an enumeration of the plants of the family Santalaceae collected in South Africa by Ecklon and Zeyher (Flora, 1857, in 2 parts, 20p). He also corresponded with, and obtained specimens from, W. Gueinzius*, C.A.W. Schmieterloew*, C.W.L. Pappe*, P. MacOwan* and H. Bolus*.
On the basis of his knowledge of South African plants W.H. Harvey* selected him as co-author of the first three volumes of the Flora Capensis: being a systematic description of the plants of the Cape Colony, Caffraria and Port Natal. The work was published in parts between 1859 and 1865, in both Dublin and Cape Town. Sonder was responsible for describing 25 families (nearly half) in Volume 1 (1859-1860), 15 families in Volume 2 (1861-1862) and 4 families in Volume 3 (1864-1865). The work was interrupted by Harvey's death and was continued by others only in the late 1890's, and finally completed in 1933. The Flora Capensis has played a very important role in the development of South African botany, enabling botanists to identify plants and establish their recorded distribution in a single source. Harvey and Sonder's initial work on this monumental publication constituted a contribution of extreme importance in the development of South African botany by putting the subject on a sound scientific basis.
Sonder was awarded an honorary Doctor of Philosophy degree by the University of Königsberg in May 1846 for his contributions to botany. That same year he was elected a member of the Kaiserlich Leopoldinisch-Carolinische Deutsche Akademie der Naturforscher of Halle. In 1875 he sold most of his Cape plants, except the ericas on which he was working, to the Swedish Museum of Natural History, Stockholm. Most of the rest eventually ended up in the Victoria National Herbarium, Melbourne. The genus Sonderina (Family Umbelliferae), which is endemic in South Africa, was named after him, as were the local Rock fig, Ficus sonderi, and other species.