German naturalist, son of the botanist Franz Carl Mertens. As a collector, Mertens gathered plants mostly as a participant on Lütke's voyage of 1826-1829 to Alaska via the Pacific Islands. Mertens was born in Bremen, where he was educated in botany by his father and studied classical languages (after serving in the Napoleonic Wars from 1813-1815). In 1817 he began studying medicine at Göttingen, completing his qualifications at Halle in 1820. He thereafter practised medicine in Berlin and Bremen, before being chosen to serve as surgeon and naturalist on board the Senyavin, sailing under Captain Lieutenant Fedor Lütke on a Russian expedition to Alaska and the Pacific (1826-1829). Twelve island groups were discovered on the voyage and another 26 in the Carolines described. Mertens was joined by ornithologist Baron von Kittlitz and mineralogist Alexander Postels, with whom he discovered more than a thousand species of insect, fish, bird and mammal new to science, plus more than 2,500 types of plant and algae. After the expedition's return to Russia in 1829 the party was sent out again, to Iceland. Mertens died within two weeks of their return to St .Petersburg in 1830. The St. Petersburg Botanic Gardens acquired his herbarium of 35,000 specimens and his collections from Alaska were published by Bongard. The hemlock Tsuga mertensiana, which he discovered on the island of Sitka, Alaska, is named after him.

Sources:
E. von Lindemann, 1885, Bulletin de la Société Impériale des Naturalistes de Moscou, 1885(1): 46-47
1888, Botanische Jahrbücher, 9: 442
M.J. van Steenis Kruseman, "Cyclopedia of Collectors", Flora Malesiana, online edn:
http://www.nationaalherbarium.nl/FMCollectors/M/MertensKH.htm.