Fern and fern green
The plain name fern is mostly known from Crayola, which made a Fern crayon in 1998. Wikipedia shows that crayon as #63B76C, a light, fresh green. Name That Color uses the same code for Fern.
The older name is fern green. Maerz and Paul's A Dictionary of Color of 1930 says it was first used as a color name in 1902. Its code, #4F7942, has its own page as fern green. The Wikipedia section on fern green covers both.
Where #548D44 comes from
The code on this page sits between those two. It is the color called "fern green" in the 2010 xkcd color survey, not "fern", which that survey gives as #63A950. So the name and the code here come from slightly different entries. For more leaf colors, see sap green or the shades of green.

