Theodor Magnus Fries, the son of Elias Magnus Fries, was a fine lichenologist who was "probably responsible for accelerating acceptance of the Schwenderian concept of lichens." The Dictionary of the Fungi The same source also says that he "edited [the] correspondence of Linnaeus and wrote 170 publications on many aspects of biology and geography."
I have to check the details of his life, which seem to have gotten confused with those of his father. The Dictionary of the Fungi has him being the professor of practical economy and his father professor of botany. Gray, however, writing in 1877, says that it was Theodor Magnus Fries who was then professor of botany, upon the retirement of Areschoug (not Fries Sr.). I can see that I'll have to do more digging on this one.