In 1759. He then practiced as a physician for the next twenty years, during which time he pursued botany as a hobby, collecting in the morning before work and then studying his accumulation in the evening. He also acquired a microscope and a small library. Skilled at both microscopy and biological illustration, he was able to identify moss antheridia and archegonia.
He directly observed the germination of spores and formation of the protonema.
He was less successful with other sporophytes, being unable to determine the life cycles of ferns or fungi, but he did make useful observations on the algae Chara and Spirogyra and he made it clear that he was not the first to get new plants from sowing the spores of mosses, C. Meese having done it before him. His chief work, Species Muscorum Frondosorum was published posthumously, in 1801.
lieutenant describes nearly all the moss species then known, and is the starting point for nomenclature of all mosses, except for the sphagnum group. In April, 1788 he was elected a Fellow of the Royal Society.
Hedwig is commemorated both by the moss genus Hedwigia as well as a journal Hedwigia.
German Academy of Sciences Leopoldina. Royal Society; Royal Swedish Academy of Sciences]
In 1790, he was elected a foreign member of the Royal Swedish Academy of Sciences.