German botanist from Strömberg, Hundsrück in Rheinland-Pfalz, who trained in natural sciences. He is perhaps best known for leading the first European botanical expedition to northern Siam (Thailand) between 1904 and 1906. Hosseus completed a PhD at the University of Leipzig (1903) with a thesis on the influences on autonomous movements of plants induced by external factors, and he was very interested in plant adaptations. After preliminary expeditions to Ceylon (Sri Lanka) and the Malay Peninsula, Hosseus travelled to northern Siam in 1904 to make botanical and ethnographic collections. His specimens were of good quality and he collected a number of duplicates which were distributed to many herbaria. Primarily interested in Acanthaceae and the Fabaceae, he often ignored many woody families but also collected zoological specimens.
Hosseus had a love of mountains and had published botanical works on the mountains near Salzburg early on in his career. Also ambitious to be the first to discover anything, living or otherwise, he enlisted the help of local porters and climbed mountains where no European had ventured before. The book of his travels, entitled Through King Chulalongkorn's Kingdom (1904-1906): The First Botanical Exploration of Northern Thailand was first published in 1912. It illustrates the day to day trials of running an expedition, but also highlights many politically, ethnographically and historically interesting observations including Shan insurrections, French administration in the young country of Laos and his own frustrations with British authorities in Siam. The book also touches on environmental issues such as forest fires, logging and early fears of species extinction as illustrated by a local deer species. Hosseus would also publish a number of additional articles on his experiences and findings while on the Siam expedition. At the end of the expedition he returned to Germany, called back due to the death of his father, but did not remain there for long.
In 1913 he moved to Berchtesgaden, Bavaria before accepting a post at the Ministry of Agriculture in Buenos Aires (1913-1915). He emigrated to Argentina and was initially an Agricultural Engineer attached to the Experimental Stations of the Agricultural Ministry of Argentina. He took part in expeditions in the following years and published a number of papers on his findings. He was appointed professor of botany at the University of Cordobá (1916-1946) and was director of the Botanical Museum there. Hosseus began to be interested in protecting the environment, especially because of the botanical diversity lost at the hands of encroaching agriculture, and in 1916 he was involved in a plan called the "Project National Park of the South". During his time in Argentina he collected extensively in South America and wrote articles on the bamboo canes of the Southern Cordilleras (1915), conifers (1927), the mosses of Córdoba (1937 and 1938) and the cacti of Argentina (1939). A fellow of the Cactus and Succulents Society of America, Hosseus resigned from the University in 1946.
It appears as though he often specialised in taxa that were little studied, and this seems to be due to an obsession with his name being attached to species or places that he had discovered. He was always concerned with things being done properly and his work being duly attributed; he once wrote of his frustrations with the British scientific working system and especially the lack of acknowledgement he received for his work from the Royal Botanic Gardens in Kew. Unfortunately there is a high level of synonymy between tha taxa that he named and those of other botanists exploring at the same time. Agapetes hosseana Diels, Buddleja hosseusiana Kraenzl., Cryptantha hossei Brand, Tephrocactus hossei Krainz & Gräser and Thunbergia hossei C.B. Clarke are some of the taxa named after him. A lake was also named in his honour, the Laguna Hosseus in the National Park Nahuel Huapí. Hosseus'character was described as conservative, sharp and perceptive.
