FIrst off, I want to start off with a except from the Elder Scrolls Wiki:

Relatively little is known about the Hist. They are first mentioned in http://elderscrolls.wikia.com/wiki/Timeline#2E_864, in the http://elderscrolls.wikia.com/wiki/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. ^{http://elderscrolls.wikia.com/wiki/Hist#cite_note-PGE1:WR-0} 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 http://elderscrolls.wikia.com/wiki/Hammerfell".^{http://elderscrolls.wikia.com/wiki/Hist#cite_note-PGE1:WR-0} The book, http://elderscrolls.wikia.com/wiki/The_Annotated_Anuad suggests that the Hist are the "Trees of http://elderscrolls.wikia.com/wiki/Argonia" ^{http://elderscrolls.wikia.com/wiki/Hist#cite_note-TAA-1} (today known as the http://elderscrolls.wikia.com/wiki/Black_Marsh). They are believed to have been around since the time of the creation of http://elderscrolls.wikia.com/wiki/Nirn,^{http://elderscrolls.wikia.com/wiki/Hist#cite_note-TAA-1} and this has since been confirmed by such sources as the http://elderscrolls.wikia.com/wiki/Pocket_Guide_to_the_Empire,_Third_Edition, where it is confirmed that they, rather than the http://elderscrolls.wikia.com/wiki/Aldmer or the http://elderscrolls.wikia.com/wiki/Nede, were likely the original forms of life on http://elderscrolls.wikia.com/wiki/Tamriel.

More recently, in http://elderscrolls.wikia.com/wiki/Cyrodiil, specifically in the city of http://elderscrolls.wikia.com/wiki/Cheydinhal, a group of mercenaries working for http://elderscrolls.wikia.com/wiki/Blackwood_Company stole a Hist tree from Argonia and used its sap, which seems to have hallucinogenic properties, to give themselves Bloodlust and strength when undertaking assignments. In reality, this caused them to be unable to distinguish reality from their own Hist induced hallucinations, and caused them to kill civilians. The tree was believed to be destroyed by the http://elderscrolls.wikia.com/wiki/Hero_of_Kvatch.

It is further mentioned later on when it states: 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 Hist seems to possess Hallucinogenic Properties, which are thought to give the user bloodlust and strength when going into battle, but in reality cause the victim to be unable to differentiate enemies and non-combatants. This is demonstrated by Blackwood Company's slaughter of civilians, seeing them as http://elderscrolls.wikia.com/wiki/Goblins. It is thought that these effects are due to the http://elderscrolls.wikia.com/wiki/Argonian race being the only ones to tolerate it properly, it causing these effects upon all other races, although this is unconfirmed.

The only known Hist Tree in Cyrodiil was destroyed by the Hero of Kvatch in the http://elderscrolls.wikia.com/wiki/Third_Era.

Back to me: Even though this kind of explains what the Hist is, what's your take on them?

The Hist play a role in the two TES novels (although I have not finished reading the second). They remind a lot of Bafforr trees from Star Wars (from Ithor, the Hammerheads' home planet): they're basically sentient and intelligent, and at the least revered, at the most worshipped. They seem to have some telepathic powers as well. Other than that, I'm not entirely sure myself.