Instead of traveling all the way back to the "start" of the instance, one simply needs to leave the area and go to the Glenn of the Unicorns. The tree spirits there will drop this root.
As a FYI, I am a 54 Wizzy, and I had NO problems with these lev 58 (non heroic) mobs.
Hope I helped a bit and saved you some time!
Almost forgot that these guy will also drop the Treecaller logs needed for the Quest, It's big, It's Heavy, It's wood. A Lev 54 Quest.
Edit: I do not know what the drop rate is for the listed mobs above, but it is VERY low for the sharpthorn tuber root in the location I am at. Edit: The Tuber roots drop from the shambler xxx in the little river/stream. Seems to be either 1 or 2 per spawn.
Edited, Sep 14th 2007 7:42am by DunedainMistMoore