Clemenz H. Wehdemann, botanist and artist, was the son of a church minister and received a good education from his father. He joined the Dutch East India Company as a soldier and came to the Cape of Good Hope in 1784. By 1789 he had risen to the rank of sergeant in the Jager Company. After the first British annexation of the Cape in 1795 he earned a living by teaching drawing. From 1799 he also studied and collected plants. When the Cape was handed over to the Batavian Republic in 1803 he was called up for military duty and became an officer. Following the second British annexation of the Cape in 1806 he elected to remain in the colony and bought the library of Joachim Itzen, which he opened in Waal Street.
After a year, during which he suffered a severe attack of smallpox, he gave up this venture and concentrated on botany, though he appears to have done some itinerent teaching too. He was particularly interested in trees, which he studied and painted in water colours. Untill 1812 he remained in the Plettenberg Bay district and in 1810 had a contract to collect specimens there for Joseph Mackrill*. By 1812 he had completed four albums of tree paintings, with descriptions, which he sold. Some of the species included were new to science. One of his albums, containing 59 paintings, is at Kew Gardens, England; a second, with 60 paintings, is in the British Natural History Museum; the third, with 62 paintings, is in the Mendelssohn Collection, Library of Parliament, Cape Town; and the fourth, with 40 paintings, is in private hands. Some species are included in more than one album.
After a brief stay in Cape Town in 1817 Wehdemannn returned to the Eastern Cape. From 1821 to 1835 he wandered mainly between the Sundays and Baviaans Rivers. During 1826-1830 he made four sets of boxes in the shape of books from the wood of various tree species, about 18 by 13 cm in size. Inside each box was placed a description and drawing of the tree, its flowers, leaves and seeds. He sold a collection of 60 of these tree books in Cape Town in 1827. A collection of 50 of them was presented to the Transvaal Museum in 1905/6 and was later bought by the Botanical Research Institute, Pretoria.
Wehdemann also studied the birds and insects frequenting different tree species and appears to have sent plants to England. Towards the end of his life he was a poor and lonely wanderer, living mainly on charity. In 1835, following the outbreak of the Sixth Frontier War, he fled to the farm Lichtenstein, owned by G.L.E. (Ludwig) Krebs*, where he remained until his death later that year.