Karl Ludwig von Willdenow and the Start of Scientific Plant Geography

In 1788 when he was 19 years old and about to enroll at the University of Gottingen, Alexander von Humboldt met Karl von Willdenow (1765–1812), a 23-year-old medical student. Humboldt already had a keen interest in natural history and his meeting with Willdenow strongly encouraged it. Willdenow was learning medical botany, and his detailed studies of plants had led him to consider how they were distributed geographically.

Willdenow was not the first naturalist to observe patterns in the way plants were distributed. Johann Reinhold Forster (1729–98) had made a similar observation earlier. Forster, with his son Georg (1754–94) as his assistant, had been the official naturalist on James Cook's (1728–79) second voyage in search of a southern continent, from 1772 to 1775. Johann Forster was a difficult man. After their return to England, he quarreled with both Cook and the Admiralty over who should write the official account of the voyage. The Admiralty finally backed Cook, leaving Forster to publish his own account at his own expense. In fact, he wrote two. The first, written in collaboration with Georg and published in 1777, was entitled A Voyage round the World in His Britannic Majesty's Sloop Resolution, Commanded by Capt. James Cook, during the Years 1772, 3, 4, and 5. The following year he published Observations Made During a Voyage Round the World, of which he was the sole author. In that book, Forster noted that within each region of the world the expedition visited, the plants and animals formed distinct units, each occupying a particular environment defined principally by temperature. As they sailed from the frigid Antarctic to the Tropics, these biological units formed a clearly defined sequence, and he noted that the tropical plants and animals were more abundant and more spectacular than those found anywhere else. Forster also recorded that the species living on islands were similar, though not identical, to those found on the nearest continent, but that Asian and American species mingled on some Pacific islands. It was the beginning of biogeography, but Forster unjustifiably extended his observations of plants and animals to human populations.

In later years, when he had become a professional botanist, Willdenow concentrated on plant distribution and avoided Forster's vague anthropological speculations. He recognized that climatic, geological, and biological factors interacted to produce regional differences in plant communities. These differences were due to plants adapting to the conditions in which they lived, but Willdenow saw that this was not a complete explanation. In many instances the plants living under similar conditions in different regions were different species and not the same species that had adapted in different ways. Willdenow saw that the climate was the most important factor determining the type and number of plant species in a particular region. He also noted that the composition of plant communities changed over time, and that occasionally plants could cross geographic barriers such as mountains and oceans, thereby expanding their range from one region to another. He observed that new species could appear and that others could become extinct. Willdenow published his most important book in 1792. It was entitled Grundriss der Krauterkunde zu Vorlesungen (translated into English and published in 1805 as Principles of Botany), and it was the book in which Willdenow laid the foundation of plant geography.

Karl Ludwig von Willdenow was born in Berlin on August 22, 1765, the son of an apothecary. He studied pharmacy at Wieglieb College in Bad Langensalza, Thuringia, graduating in 1785 and then enrolling at the University of Halle, where he studied medicine and botany. He graduated in medicine in 1789, and the following year he took over his father's apothecary business. Willdenow worked as an apothecary until 1798, but combined this with his continuing study of plants and their distribution. In 1794 he became a member of the Berlin Academy of Sciences. In 1798 he was appointed professor of natural history at the Berlin Medical-Surgical College, and in 1810 he was made professor of botany at the University of Berlin. In 1801, the year he became director of the Berlin Botanical Garden, he was appointed principal botanist to the Berlin Academy of Sciences. Willdenow had the botanical garden replanted, grouping the plants according to the part of the world and the type of habitat where they were found. Plant collectors, including Humboldt, sent him specimens from all over the world, and he assembled a large herbarium, which the botanical garden purchased in 1818 after his death. In 1807 Humboldt obtained funding for Willdenow to expand the garden. Willdenow remained director of the botanical garden until his death in Berlin on July 10, 1812.