German botanist. Born in Bremen, Cornelius Osten had shown a great passion for botany since childhood, collecting many natural history works and admiring the beauty of the plates within them. At the age of 23 he emigrated to the Rio de la Plata area of Uruguay, built a successful business and in 1907 his herbarium in Montevideo already contained some 2,000 specimens. He took part in excursions throughout the area, from the banks of the Rio de la Plata into the interior, travelling to Mendoza and Cordoba (Argentina) with his family including his brother, the astronomer Hans Osten. However his most fruitful travels were in Paraguay with the doctor Émile Hassler and his student Teodoro Rojas. He sent many duplicates of his collections to the museums of Berlin-Dahlem, Washington and Buenos Aires.

The family that always captured his attention was the Cyperaceae, which he studied for over 20 years with fellow German botanist Georg Kükenthal. He began to write a Flora Uruguaya, publishing Pterophytes in 1924, followed by the gymnosperms, protomonocotyledons, grasses and finally in 1931 his best work, Las Ciperaceas del Uruguay. The publication of the latter began a new era of botanic knowledge in Uruguay. On the 70th anniversary of Goettingen University he was awarded an honorary doctorate and praised for the prestige he had brought to the German nationality in South America. By the time of his death his collection numbered between 26,000 and 28,000, the largest in Uruguay, which he handed over to the National Museum of Natural History in Montevideo. Osten was said to be extremely open spirited, intent on improving the quality of his knowledge in all areas of the sciences, arts and geography and had a good knowledge of the classical languages.