German systematic botanist who served at the Berlin-Dahlem Botanic Gardens from 1921-1945. Ludwig Diels was born in Hamburg, but grew up in Berlin, where his father was a classical scholar at the university and served as secretary of the Academy of Science. After his schooling Diels stayed in Berlin, studying botany and geography, the former under Adolf Engler. He completed a doctoral thesis on the vegetation of New Zealand (1896) and became an assistant to Engler, with whom he published several monographs. At this time he also wrote an article on ferns for Engler and Prantl's Pflanzenfamilien.

After defending his PhD Diels made plans to travel to New Zealand as part of a tour of the southern hemisphere. Gaining funds from the Humboldt Foundation for Nature and Research Travel, he embarked on this ambitious voyage in 1900 with fellow botanist Ernst Pritzel. Over the course of two years they explored South Africa, Australia and New Zealand, spending more than half the time in Western Australia, where they traversed inland to Lake Austin and the goldfields around Menzies, and to Champion Bay, Cape Leeuwin and Esperance on the coast. Diels amassed 4,700 specimens on this leg of the trip, with Pritzel providing a further thousand.

Returning to Berlin (via Java) in 1902 they collated their results in several extensive works published between 1904 and 1906. In particular their joint work, "Fragmenta Phytograghiae Australiae Occidentalis", in Botanische Jarbücher (vol. 35, 1904-1905), became an authoritative text on West Australian flora, as did Diels' Die Pflanzenwelt von West-Australien Südlich des Wendekreises (1906) in Engler and Drude's Vegetation der Erde (Vegetation of the World) series. Observations made on this voyage also led to his monograph of the Droseraceae, published in Engler's Pflanzenreich, for which he also monographed the Minispermaceae. Around this time he also began his research into the Chinese flora, on which he published lengthy articles such as Plantae Forrestianae (1911-1913).

Diels accepted a position at the University of Marburg in 1906, taking with him his new wife, Gertrud Biesenthal, who bore him three children. Their happy family life was complemented by his work on plant geography and systematics over the next eight years, alongside duties as assistant professor (from 1908). They returned to Berlin in 1914 when Diels was recruited as Assistant Director at the Botanical Garden and Museum in Dahlem (1914), taking over from Ignatz Urban. (He was not required to serve in the First World War thanks to an injury to his skull suffered in the Alps.) When Engler retired as director in 1921, Diels succeeded him and was appointed to a professorship at the University of Berlin. He was later named Director-in-Chief of the museum and gardens (in 1928) and elected to the Academy of Science. Further honours were bestowed upon him in the form of corresponding memberships to many learned societies in Europe, Australia, New Zealand and the United States, while in 1930 he was awarded an honorary DSc at the International Botanical Congress in Cambridge. At the height of his career, he undertook his next major expedition, making a long-desired journey to Ecuador in 1933, combined with a lecture tour of North America. His journey in the Andes resulted in his important work, Beiträge zur Kenntnis der Vegetation und Flora von Ecuador, published in 1937.

Events took a down-turn after Diels' return to Germany. The success of the Nazi party and the ideology to which Diels was obliged to acquiesce, as the leader of a national institution, displeased him. Around this time he also suffered a tragedy when his son was killed in an air disaster. One of the brighter occurrences of the late 1930s was the revival of his connection with Australia, as the Australian botanist Charles Gardner visited Berlin and took with him samples from Diels' specimens. A far darker time lay ahead, though. Most of Diels' plant collections were deposited at the herbarium at Berlin-Dahlem, which was destroyed in an air strike in March 1943. The loss of his specimens, many of which were holotypes, along with many other irreplaceable collections and the museum library, was a terrible blow for the ageing botanist. When he died in Berlin two years later, the Botanic Gardens were in a lamentable state, having lost their greenhouse stock for lack of coal for the heating system and the landscape having been turned literally into a battlefield. Diels was buried in the gardens alongside his predecessor, Adolf Engler, and is remembered as one of Berlin's great systematists.

Sources:
J.S. Beard, 2001, "The Botanists Diels and Pritzel in Western Australia: A Centenary", Journal of the Royal Society of Western Australia, 84: 129-134
T. Eckardt, 1966, "150 Jahre Botanisches Museum Berlin (1815-1965)", Willdenowia, 4(2): 173
H. Melchior, 1955, "Ludwig Diels, 1874-1945", Berichte der Deutschen Botanischen Gesellschaft, 68a(4): 281-287
J. Milbraed and R. Pilger, 1947, Proceedings of the Linnean Society, 159(2): 148-151
H. Ziegenspeck, 1952, "Necrologia: Ludwig Diels 1874-1945", Revista Sudamericana de Botanica, 10: 53-54.