Sir Joseph Dalton Hooker OM GCSI CB MD FRS ( 30 June 1817 â `` 10 December 1911 ) was a British botanist and explorer of the 19th century . Sir Joseph Dalton Hooker OM , GCSI , CB , MD , FRS ( 30 June 1817 -- 10 December 1911 ) was one of the greatest British botanists and explorers of the 19th century .