Relatively little is known about the Hist. They are sentient trees native to Black Marsh that seem to all be connected together through a hive-like system. They are first mentioned and wrongly referenced in 2E 864, in the Pocket Guide to the Empire, First Edition, where it is written that "Argonians are rarely seen outside of their homeland, except for a relatively intelligent strain called the Hist." 
The guide further adds that they are "repulsive, but peaceful enough to be tolerated among the human kingdoms, and can be found as far as western Hammerfell".. It has also been suggested that the Hist are the "Trees of Argonia"  (today known as the Black Marsh). This is the more accepted theory.
The Hist are thought to share a mind or have a hive mind ability. Though they share a mind it is possible for one to go rogue and "escape itself". In such instances, the Hist purge the rogue tree. This last happened to a tree in Lilmoth over 300 years ago. The current Lilmoth Hist grows from part of its root. 
Hist sap has hallucinogenic properties when used by non-Argonian species, causing them to perceive civilians and actual enemies alike as hostile to them. Only Argonians may ingest the Hist sap to feel its full effects without negative reactions.
The Hist also seem to have the ability to communicate telepathically with people who ingest their sap. 
It has been suggested that the Argonians are co-dependent on the Hist.
They are believed to have been around since the time of the creation of Nirn, and this has since been confirmed by such sources as the Third Edition of the Pocket Guide to the Empire, where it is stated that they, rather than the Aldmer or the Nedics, were likely the original forms of life on Tamriel..
As the apparent first inhabitants of Nirn they are believed to have created the Argonian race. 
In Cyrodiil, a group of mercenaries known as the Blackwood Company used the sap from a Hist Tree to give themselves bloodlust and strength in battle. This caused them to have hallucinations, and forced the Hero of Kvatch to destroy the tree.
It is believed that the Hist were able to prophesy the coming of the Oblivion crisis, and were able to call the "people" back to Black Marsh. It is also believed that they were able to co-ordinate the defense of Black Marsh and defeat the forces of Mehrunes Dagon. Apparently, they also "drove the Empire into the sea, and laid waste to their ancient enemies in Morrowind".
The Argonians of Black Marsh worship this unique and intelligent tree as an almighty power that guides and creates their souls. While little is known on the worship of this tree by the Argonians, it is confirmed that this represents the core of Argonian religion and culture. In fact, Argonian hatchlings drink the sap of the hist at birth and during their infancy.
According to legend, the sap of the hist tree when consumed gives the hatchling its soul, and when that Argonian dies, their soul travels back to its hist tree and is stored until another hatchling drinks that hist and is given its soul, creating a cycle of rebirth.
It is further mentioned that, "Rumors and speculation also abound regarding the Hist, a species of giant spore tree growing in the innermost swamps of Argonia. Some have maintained that natives worship the trees; others claim the trees are, in fact, a sentient race, more ancient than all the races of man and mer."
No reliable accounts of expeditions into central Argonia exist to lend credence to these claims, and modern Argonians are reticent to speak of the mysterious trees.
- The Elder Scrolls III: Morrowind (Mentioned only)
- The Elder Scrolls IV: Oblivion
- The Elder Scrolls V: Skyrim (Mentioned only)
- ↑ 1.0 1.1 Pocket Guide to the Empire, First Edition: Wild Regions
- ↑ 2.0 2.1 The Annotated Anuad
- ↑ 3.0 3.1 3.2 3.3 3.4 http://www.imperial-library.info/content/infernal-city
- ↑ Ancient Tales of the Dwemer, Part II
- ↑ Pocket Guide to the Empire, Third Edition: Eras
- ↑ The Monomyth
- ↑ Pocket Guide to the Empire, Third Edition: Black Marsh
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