It has been said by many characters and books throught the The Elder Scrolls that the Hist are a race of trees as old - or even older - than Nirn. I was investigating on in the Imperial Library when I discovered these incredible facts (all quotes and facts are from the Infernal City and the Lord of Souls):
Quote: “The Hist were many, and they were one. Their roots buried deep beneath the black soul and soft white stone of Black Marsh, connecting them all, and thus connecting all Saxhleel, all Argonians. The Hist gave his people life, form, purpose. It was the Hist who had seen through the shadows to the Oblivion crisis, who called all the people back to the marsh, defeated the forces of Mehrunes Dagon, drove the Empire into the sea, and laid waste to their ancient enemies in Morrowind"- The Infernal City
Fact: Though the Hist 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.- The Infernal City
Quote: From Delia Huerc, a Redguard traveling with Minister Hierem: “The [ Hist] tree [in Lilmoth] is enormous. The only one I have ever seen taller was in Valenwood, but the Hist was more massive, more spread out. And I could feel a palpable presence in it. I had never quite credited the Argonian claims that the trees are intelligent, but when I stood in its presence, I could no longer doubt it. Further, I thought I felt a certain malevolence in it, but that might well have been my imagination, for the whole situation was anything but friendly. The An-Xileel have been uniformly rude and arrogant, the city itself is a festering, putrid place. From the moment I entered Lilmoth, I have wanted nothing more than to leave it.The minister, on the other hand, seems quite excited, almost jubilant.The An-Xileel sang to the tree, an awful cacophonous chant that went on so long that I might have drifted off a bit. At some point, Hierem added his voice to theirs, but in a sort of counterpoint. He lit a brazier, and I’m sure he did some sort of sorcery. In his younger years he was in the leadership of the Mages’ Guild, before that organization utterly collapsed, and so I know him capable of these things, but I was still somehow surprised.It was my impression that he was calling something, for he repeated the word “Umbriel” many times. It seemed like a name, although the language he spoke was not one I knew, and so I may have been mistaken, for nothing came, although everyone seemed pleased anyway.”- Lord of Souls
Quote: "The Hist 'are sentient trees', and we [Glim, speaking on behalf of the Argonians] are connected to them. They are many and they are one, all attached at the root, and we, too, are joined to that root. Some say we were created by the Hist, to see for them the world where they cannot walk. They can call us or send us away. When we are named, we take of the sap of the Hist, and we are changed—sometimes a little, sometimes very much..."- Lord of Souls
Quote: “A few twelves of years ago, our country was invaded from Oblivion. The Hist knew it was going to happen, and called our people back to Black Marsh. Many of us were altered, made ready for the war that we had to fight. Made stronger, faster—able to endure terrible things. ...”- Lord of Souls
Quote: “The Hist are supposed to be unified,” Glim said, “but at times certain trees have gone rogue, broken away from the others. It happened long, long ago in my city, and I think it happened again, not long before your world entered mine. A rogue tree helped Umbriel somehow, do you understand? It helped kill many, many of my people so they could serve Umbriel as dead things. And now I think it may have helped summon Umbriel here in the first place."- Lord of Souls
Fact: The sap of the Hist can “alter things.”- Lord of Souls
Well from quotes and facts from both of these books, it seems that the Hist are incredibly powerful. Here are the abilities the Hist seem to possess:
It seems that the Hist have a physical or at least mental connection with the Hist, and are able to contact them wherever they are, and when they need them. Evidence to support this is a random rumor you may hear in Elder Scrolls Oblivion, about Argonians vanishing into the swamps. This may be the reason why. Remember that Dagon's forces were attacking Black Marsh? The Argonians weren't just leaving - the Hist were calling them home to fight.
The Hist were able to forsee many events concerning the Argonians before any of them happened, suggesting clairvoyance is a trait among the species.
Interestingly, the Hist seem to be a collective conscious, with at least one tree being locate in every major Argonian city (maybe to keep an eye out for them?)
Hist sap seems to be able to physically and mentally alter Argonians, bringing up a question that makes really wonder: Were the Argonians always lizards?
Hists can go rogue, which usually leads to diastrous events (read the books if you haven't - because of a rogue Hist tree the entire Argonian race was almost eradicated.
Lizards Lizards Lizards
Now let's move on to Argonians.
Fact: Roughly 10 miles from Lilmoth is “an upthrust rock that towered more than a hundred feet above the jungle floor. It seemed unclimbable, but ... Glim led [Annaig] to a cave opening in the base of the soft limestone. It led steadily upward, and in some places stairs had been carved. Faded paintings that resembled coiled snakes, blooming flowers, and more often than not nothing recognizable at all decorated the climb, and an occasional side gallery help often bizarre stone carvings of half-tree, half-Argonian figures. ... moss and low ferns [grow] on the flat summit of the tabletop.”
Fact: “It was generally believed that Argonians had been given their souls by the Hist, and when one died one's soul returned to them, to be incarnated once more. [To Glim,] that seemed reasonable enough, at least under ordinary circumstances. In the deepest parts of his dreams or profound thinking were images, scents, tastes that the part of him that was sentient could not remember experiencing.”
Fact: “The concept Imperials called 'time' did not have a word in [Glim's] native language [Jel]. In fact, the hardest part of learning the language of the Imperials was that they made their verbs different to indicate when something had happened, as if the most important thing in the world was to establish a linear sequence of events, as if doing so somehow explained things better than holistic apprehension.”
Fact: “To [Glim's] people – at least the most traditional ones – birth and death were the same moment. All of life – all of history – was one moment, and only by ignoring most of its content could one create the illusion of linear progression. The agreement to see things in this limited way was what other peoples called 'time'.