German botanist and explorer who made significant collections in Argentina and significant studies of mosses in Europe and South America. Born in Kahla (Thüringen) to a local politician, Lorentz studied theology at Jena and Erlangen, taking a supplementary course in botany. Completing his studies in theology in 1858 he began to concentrate his efforts on botany, studying under C.W. von Nägeli in Munich and developing a special interest in mosses. He ranged far and wide to collect specimens of the latter, from the surrounding Black Forest, Austrian Alps, Switzerland, northern Italy and Scandinavia.

In 1860 he completed his doctorate and began working with Wilhelm Philipp Schimper on Geographie der Moose (Geography of mosses). He also went on many collecting trips with his associate Ludwig Molendo, mainly in the Alps. Until 1869 he lived in Munich, focusing on mosses and working as a private tutor in botany from 1864.

A turning point in his life came in 1870, when he crossed the ocean to Argentina to take up the post of Professor of Botany at the University of Córdoba. Lorentz embarked on a series of botanical excursions in his new home, reaping extensive collections and exploring unknown areas. The first took place in 1871-1872, when he explored the mountainous regions of Tucumán and Catamarca with the geologist Alfred Wilhelm Stelzner. The rich array of vascular specimens gleaned from this trip he sent to August Grisebach in Gothenburg, keeping the bryological material for his own studies. Grisebach described the vascular portion in Plantae Lorentzianae (1874). In the next two years Lorentz travelled with his assistant, Georg Hieronymous, through the northern provinces of Jujuy and Salta, continuing by the Bermejo River (Rio Vermejo) into the lowlands of the Gran Chaco and Bolivia. Collections from this trek are described by Grisebach in Symbolae ad Floram Argentinam (1879) together with Lorentz's later collections from Entre Rios. The lichens from this trip were sent to A. von Krempelhuber and the hepaticae to Carl Müller.

In 1874, political events forced him to leave his post in Córdoba and base himself in Concepción del Uruguay in the province of Entre Rios, where he taught natural history at a college. On arrival, however, he was stricken by an attack of smallpox that laid him low for some time. Recovering, he began to explore the eastern region, resulting in his work on the vegetation of Entre Rios (1878). In 1879 he set off on another expedition with Gustavo Niederlein across the Argentinian Pampas to the Rio Negro (travelling alongside General Roca on his 'Conquest of the Desert'). The following year he visited Sierra Ventana and in 1880 found time to marry, but his future with Johanna Frantz was cut short when a fatal liver disease overcame him in 1881, aged 46. His lifetime's achievements were nevertheless significant, contributing to major works on the botany of Argentina and further afield and writing many papers on mosses in Europe. He discovered more than 200 new species of moss, many of which are named after him.

Sources:
J-P. Frahms and J. Eggers, 1995, Lexikon Deutschsprächiger Bryologen: 295
V.A. Funk and Scott A. Mori, 1989, A Bibliography of Plant Collectors in Bolivia: 12
G. Sayre, 1975, "Cryptogamae Exsiccatae: an annotated bibliography of exsiccatae of algae, lichens, hepaticae, and music. V. Unpublished Exsiccatae: I. Collectors", Memoirs of the New York Botanical Garden, 19(3): 362
A. Stelzner, 1882, "Zur Erinnerung an der Dr. Paul Günther Lorentz", Botanisches Centralblatt, 9: 450-468
W.B. Turrill, 1920, "Botanical Exploration in Chile and Argentina", Kew Bulletin of Miscellaneous Information, 2: 62-63.