Alfred Rehder (4 September 1863, Waldenburg, Saxony – 25 July 1949) was a horticulturist and taxonomist who worked at the Arnold Arboretum of Harvard University. Rehder was a newspaper writer from Germany who was originally hired as a laborer at the Arnold Arboretum. His talents for horticultural plant taxonomy were soon recognized, however. Early in his employment he was sent to Europe to purchase books for the library at the Arboretum. When the Journal of the Arnold Arboretum was started in 1919, Rehder was co-editor, along with the Arboretum director, Charles Sprague Sargent. Rehder produced a new edition of Manual of Cultivated Trees and Shrubs and authored the Bibliography of Cultivated Trees and Shrubs and The Bradley bibliography. He was co-author, with Ernest Henry Wilson, of Plantae Wilsonianae and A Monograph of Azaleas.