Bring Lorvarius' wind-devil to the clouds of red mist in the Crimson Expanse, near the water, and then return with a sample.
Gather a sample of the red mist
I'm no druid, but some of these mushrooms do not look to be naturally occurring. I know that our Stone Lord friend over there is eager to blame this on exposure to Azeroth, but I suspect more domestic causes.
I saw some clouds of red mist to the northeast, near the water's edge. They seemed to be spurring new growth in their wake. Take one of my wind-devils with you and get me a sample from those clouds. You may have to stay close to the ground to spot them.