Need... Water... Badly...

Seems people are having trouble finding this guy, I did at first too.
First and foremost, you must have unlocked the Druids of the Talon.
If this is true, continue, if not, do that first.
Next, you need to have done "Into the Fire" and gone down into the cave. After a little bit of starter cave tunnels, with Thisalee Crow at the end, it opens up into a pretty familiar layout, with slight tweaks. The mobs are part of the dailies you get from her and can be done while working towards Anren Shadowseeker.
Head to the left and down, there is an area with sleeping hounds, in a sort of separate cave room ahead. Turn right and take the narrow path down between the wall and a large rock, to the large open room surrounded by lava. Your target is in the back left corner as you enter this room, 5 or so little islands off the main one, laying down with a "!" waiting for you. Talk to him, and you're off. Hope this helps!

I had a hard time figuring out how to even access this quest. Here's the info that helped me. As other commentors said, you can only pick up either the Shadow Wardens of Druids of the Talon quest at once.

So first, do the daily quests in Malfurion's Breach. Today for me, they were "Embergris," Aggressive Growth," "Burn Victims," "Hostile Elements," and "The Harder they Fall."

After you turn those in, you talk to General Taldris Moonfall - he gives two quests - "The Forlorn Spire" and "Into the Fire" - I was taking both of them, not realizing you can only do one (but wondering why one only popped up for me to do). For the "Save Anren Shadowseeker" achievement, you need to pick "Into the Fire."

And The Mysterious Seed is started from [item=69675], which you get by killing a random Druid of the Flame in Widow's Clutch. Edit: Getting downrated for adding useful information? Makes sense.