Skyrim:A Return To Your Roots

Quick Walkthrough
# Collect thirty samples of the mysterious Crimson Nirnroot.
# Take these samples to Sinderion's colleague Avrusa Sarethi so that Sinderion's research may continue.

Detailed Walkthrough
thumb|right|Seemingly unreachable Crimson Nirnroot, which can be harvested with a Skyrim:Whirlwind Sprint|Whirlwind Sprint.
The "Noisy Red Weed"
Sinderion had been obsessed with Crimson Nirnroot since purchasing a plant from a passing adventurer wanting to get something for the "noisy red weed" he found. Sinderion compensated the man, and then left Skingrad to set up a laboratory in Blackreach, the only known habitat of Crimson Nirnroot.

Continue the Research
The quest begins upon the collection of a sample crimson nirnroot in Blackreach. Your journal will update to reflect your part in finding out the significance of this plant. In order to get started, begin at the beginning in Sinderion's Field Laboratory. The research facility is located in Blackreach, right across from the gates of Alftand Cathedral. Inside you will find Sinderion's remains still clutching his field journal. After reading the journal, the quest will update requesting that you collect thirty Crimson Nirnroot samples from Blackreach - a difficult but rewarding task.
Locating the Samples
There are forty-four samples of Crimson Nirnroot within Blackreach (including some inside Blackreach's buildings).  Unlike the more common garden variety Nirnroot, the Crimson Nirnroot does not solely grow near bodies of water. Many plants are found near patches of mushrooms, Dwemer pipes or along the sides of the cavern. Since there are forty-four plants, all required samples can be collected at one time if you thoroughly explore Blackreach (see the Crimson Nirnroot article for more details on plant locations).  Alternatively, if you are having a hard time finding enough plants, they will respawn. Leaving Blackreach for ten days allows you to collect another sample from any previously-harvested plants.
A Job Well Done
After collecting the required number of plants, the quest will update again and you will be asked to deliver them to Avrusa Sarethi, Sinderion's former colleague. She is currently residing at Sarethi Farm, between Riften and  Ivarstead.
Give Avrusa the thirty Crimson Nirnroot samples to complete the quest and receive The Nirnoot Missive. You will also be provided with Sinderion's Serendipity, an ability which provides a 25% chance to mix two potions instead of one.

Notes
The Alchemy perk Green Thumb does not affect Nirnroot and therefore cannot be used to decrease the number of plants needed to be harvested.
The quest is a sequel to the Oblivion quest, Seeking Your Roots.

Bugs
 
if you consume all the Crimson Nirnroot in your inventory, not only will that amount be redacted from the quest counter, but the counter will even count the removed roots twice, potentially causing the counter to go into the negatives.
The quest may update telling you to return the nirnroot and stating you have found 30 samples when you have actually found less. Once you have the required amount, you will be able to return it and the quest should continue as normal.
Once all thirty Crimson Nirnroots have been collected the option to give them to Avrusa is not there, thus freezing the quest.
Simply drop one and pick it back up to continue the quest.
If you place Crimson Nirnroot in a container or follower's inventory, or otherwise remove it from your inventory, the appropriate number may or may not be removed from the quest log.
To complete the quest even if the quest log does not represent the actual amount of Crimson Nirnroot you have in inventory simply go to Avrusa with thirty in your inventory, and the quest will complete itself without updating in the journal.
The number of Crimson Nirnroot in the quest log is thrown off if you transfer them to or from a container in groups. If you place more than one in a container at one time the quest log will think you only moved one. The quest log number can be corrected by placing them in a container and pulling them out individually (e.g., it says you have nine but you have ten: place two in a container at one time, and then pull them out one at a time). You can also get the quest log up to 30/30 with this method, but you cannot complete the quest without thirty in your inventory.
  To fix the count directly, use the console commands:   and   . Note that this will not cause the quest to advance if set directly to 30. To do so, drop one and pick it up again.
 
This bug can be fixed by reloading a previous save. If reloading does not work, you can try picking up other samples of the Crimson Nirnroot.
 
To fix this, just find one more Crimson Nirnroot and the quest marker will reappear along with the "Completed" text.

Quest Stages