Carl (or Karl) L.P. Zeyher, a professional plant collector, was the son of a gardener, Johann J. Zeyher, and his wife Anne C. M?llerin. As a youth he worked for his uncle, Johann M. Zeyher, head gardener to the Grand Duke of Baden at Schwetzingen. His first publication was a list of the plants in the Duke's garden, Verzeichnis der Gew?chse in den Grossherz. Garten zu Schwetzingen (Mannheim, 1819). In August 1822 Carl accompanied the commercial collector of natural history specimens, W.W. Sieber*, on the first leg of a collecting trip around the world. They arrived at the Cape of Good Hope in October that year, where Zeyher was left to collect plants. Sieber returned to the Cape in April 1824 and took the collection to Europe to be sold. Zeyher remained behind to continue collecting for him, but as he received no payment he began to collect for his own account. In 1825 he travelled eastwards to Uitenhage and in 1828 northwards to beyond Clanwilliam. His plants were sent to his uncle at Schwetzingen, but following the latter's death the Baden government took possession of most of the material.
In 1829 Zeyher and the botanist Christian F. Ecklon* entered into a partnership, agreeing to coordinate their botanising and pool the resulting collections. Ecklon went to the Eastern Cape, while Zeyher travelled to the Cedarberg and the neighbourhood of Clanwilliam, followed the Olifants River to its mouth, and signed his name, dated 1829, in the cave known as the Heerenlogement. He then went on to the Kamiesberg and northwards to the valley of the Orange River, eventually reaching its mouth. Returning to the Western Cape he met Ecklon at Tulbagh and together they climbed the surrounding mountains, where they collected many interesting mountain plants. From about October 1831 he accompanied Ecklon on a collecting trip lasting almost two years to the eastern border of the colony. They travelled over the Hottentots-Holland Mountains to Caledon, Cape Agulhas and Swellendam, through Kogmanskloof to the Little Karoo, south again to George and Knysna, and through the Langkloof to Uitenhage and Algoa Bay. From there they sent their collections to Cape Town by boat, and set off to collect in the Albany and Somerset East districts and north to the vicinity of present Queenstown. Ecklon returned to Cape Town in 1832 and left for Hamburg to sell their collections. He prepared a catalogue of Cape plants, with Zeyher as co-author, entitled Enumeratio plantarum Africae australis extratropicae.... Three parts, totalling 400 pages, were published in Hamburg between December 1834 and April 1837. Their collecting was not very profitable, financially speaking, as the prices of their specimens gradually declined owing to a declining interest in Cape plants.
For some time Zeyher worked as a gardener for Joachim Brehm* in Uitenhage. He collected numerous plants in the neighbourhood, which he sent to London to be sold under the patronage of Sir W. Hooker, director of Kew Gardens. His collection of the fungi of the district was studied by M.J. Berkeley, who published an "Enumeration of fungi collected by Herr Zeyher in Uitenhage" in the London Journal of Botany (1843), listing 13 new species and describing a new genus. Much of Zeyher's time was spent in preparing an extensive collection of Cape trees, including sections of the wood and dried specimens of the foliage, flowers and fruit. This collection was to be sold to the Berlin Museum, but was lost when the ship on which it was dispatched was wrecked. Zeyher also collected sea shells in the Eastern Cape, most of which went to the Berlin Museum. The marine molluscs Marginella zeyheri and Gibbula zeyheri, and the freshwater species Unio zeyheri, were named after him.
In November 1839 Zeyher was commissioned by the Earl of Derby to accompany the latter's gardener, Joseph Burke* on a collecting expedition. Burke reached Uitenhage in July 1840 and after several months of preparations they set out in November, travelling via Grahamstown and Cradock and reaching Thaba Nchu in February 1841 after a difficult crossing of the swollen Caledon River. Continuing northwards they crossed the Vaal River and met the Voortrekker leader, Commandant A.H. Potgieter, at present Potchefstroom in May. Moving on to the foot of the Magaliesberg west of where Pretoria was later established, they spent the next six months collecting in the area. During this time they obtained the skins of many large mammals and visited the salt pan in Tswaing crater, north of the Magalliesberg. The most northerly point reached by them was near the junction of the Crocodile and Pienaars Rivers, in September. On 17 November they were visited by the Swedish naturalist and traveller J.A. Wahlberg*. The next month they started their return journey. Travelling via Potchefstroom and Thaba Nchu they crossed the Caledon and Orange Rivers, turned westwards to Colesberg and on to Beaufort West and through the Hex River Pass, arriving in Cape Town in June 1842. The next month Burke left for England with a vast collection of birds and other animals (including live ones), plants, bulbs and seeds. Most of the expedition's plants were collected by Zeyher, as Burke was primarily interested in antelopes. They were the first, and for many years the only, significant plant collectors in the Transvaal. Zeyher's journal of the expedition was published in four parts as "Botanical notices on a journey into the interior of southern Africa in company with Mr Burke" in the London Journal of Botany (1846, Vol. 5, pp. 109-134 and 313-344; 1855, Vol. 7, pp. 326-334 and 362-370).
In 1843 Zeyher made another collecting trip to Namaqualand and the next year went to London to arrange for the sale of his collections. He also visited his birthplace in Germany before returning to Cape Town in 1847. To cover his living expenses he sold his personal plant collection to Dr C.W. Ludwig Pappe* and for some time worked on the collection in the latter's house. Pappe was a strong supporter of the movement to establish a proper botanical garden in Cape Town and when this was achieved in 1848 Zeyher was employed as collector and botanist. However, he was dismissed in February 1850 and a more practical gardener, James McGibbon*, employed to make the garden financially viable. None the less Zeyher appears to have continued collecting for the garden, as he was still listed as its collector and botanist in the Cape of Good Hope almanac for 1852 and 1853. He also collected and grew bulbs, to be sold in Germany, in a garden on the property "Zoar", in St Johns Street, where he still resided in 1856. Later he rented a cottage and a piece of ground on the estate Leeuwenhof, where he grew vegetables. He died in the smallpox epidemic of December 1858.
Zeyher was well liked by all with whom he came into contact and was one of the most important plant collectors in South Africa. The genus of South American plants Zeyheria and the genus of English plants Zeyherella were named after him, as were many local species, including Orothamnus zeyheri (by Pappe), Erythrina zeyheri (by W.H. Harvey*), and Combretum zeyheri and Rhus zeyheri (by O.W. Sonder*). His personal herbarium, relabelled by Pappe, is in the Compton Herbarium, Cape Town, while specimens collected by him are to be found in many European herbaria.