For those that have completed the Dark Brotherhood questline, you receive 1 piece of Jarrin Root from Astrid as a means of poisoning the emperor. This is the only instance/opportunity you have of obtaining said root. With the addition of a mod, its possible to plant & grow this particular root in a heathfire homestead. Does this conflict with lore?

Little to nothing is known about Jarrin Root outside of this circumstance to my knowledge. Should one be able to reproduce this root? Did Bethesda intentionally prevent one from reproducing or was it just a oversight?

I think it should be rare, like very rare, but not so much that you can only get your hands on that one piece. Unless it just doesn't grow in Skyrim.

Anyway, I was very disappointed. Astrid said a bite was enough to kill you, so naturally I had to try. It hardly did any damage, and I wasn't very high level at the time.

Supposedly it has the most lethal potential of any ingredient in the game. I've always enjoyed playing as a alchemist & I was somewhat disappointed with the poison options available to us in Skyrim. Paralysis potions certainly are worth noting but they break most encounters. My initial thought on Jarrin Root was Bethesda didn't include because it would be gamebreaking, but why go through the trouble of allowing it to be combined with other ingredients then if it is only to be used once? I'm more or less trying to get a feel & or knowledge from the community on this particular plant to determine whether or not it would be lore friendly to reproduce it in limited quantities.

For example: 1 plant per legendary completion or something to that effect.

Is this plant from Skyrim? Why is it so limited? Do you think a legendary alchemist could reproduce such a plant? My entire hearthfire home is dedicated to alchemy.

Edit: After doing some additional research apparently it comes form a rare plant which is unique to the island of Stros M'Kai....

I would assume the soil of Skyrim would be unfit to nourish such a plant. What a damn shame...

It would make sense an assassin would grow something actually useful, so even if it was rare, they would still go out of their way to obtain a plant and grow it. Mine has not as far as I know, but when I come across that mod it will likely be added. The PC character who will be started soon will also be an assassin, so the mod would be handy.

I doubt it was an oversight on Bethesda's part, the root is not available for sale in Skyrim, and not grown anywhere in the vanilla game, so no reason to let us grow it in the DLC. Does not mean it would be against lore to do so. We know it exists, it is a plant, and we have a greenhouse if it is fussy about conditions. Skyrim has a fair range of weather conditions anyway.