Gondor and Dol Amroth

[Findegil]

The Silvian-Elves of the dale of Anduin were of a mixed origin. They were all Lindai that means members of the third clain. But some of them were of Lenwes people how refused to cross the Hithaeglir. Some were Avari that wandered west and joined up with the peoples of Lenwe. And some were Sindar that came back after the drowning of Beleriand.

Respectfully
Findegil

[Tar-Elenion]

The Silvan Elves seem to have been a mix of Eldar and Avari.

"But though Mithrellas was of the lesser Silvan race (and not of the High Elves or the Grey) it was ever held that the house and kin of the Lords of Dol Amroth was noble by blood as they were fair in face and mind."
Unfinished Tales

Of course we have:
"The Silvan Elves (Tawarwaith) were in origin Teleri, and so remoter kin of the Sindar, though even longer separated from them than the Teleri of Valinor. "
op. cit.

And:
"The Silvan Elves hid themselves in woodland fastnesses beyond the Misty Mountains, and became small and scattered people, hardly to be distinguished from Avari;

but they still remembered that they were in origin Eldar, members of the Third Clan, and they welcomed those of the Noldor and especially the Sindar who did not pass over the Sea but migrated eastward [i.e. at the beginning of the Second Age]."
op. cit.

We also have:
"...the Lindarin elements in the western Avari were friendly to the Eldar, and willing to learn from them; and so close was the feeling of kinship between the remnants of the Sindar, the Nandor, and the Lindarin Avari, that later in Eriador and the Vale of Anduin they often became merged together."
Quendi & Eldar, WotJ


And:
"This resentment on the part of the Avari is illustrated by the history of PQ *kwendi. This word, as has been shown, did not survive in the Telerin languages of Middle-earth, and was almost forgotten even in the Telerin of Aman. But the Loremasters of later days, when more friendly relations had been established with Avari of various kinds in Eriador and the Vale of Anduin, record that it was frequently to be found in Avarin dialects. These were numerous, and often as widely sundered from one another as they were from the Eldarin forms of Elvish speech; but wherever the descendants of *kwendi were found, they meant not 'Elves in general', but were the names that the Avari gave to themselves. They had evidently continued to call themselves *kwendi, 'the People', regarding those who went away as deserters ... The Avarin forms cited by the Loremasters were: kindi, cuind, hwenti, windan, kinn-lai, penni ... The form penni is cited as coming from the 'Wood-elven' speech of the Vale of Anduin, and these Elves were among the most friendly to the fugitives from Beleriand, and held themselves akin to the remnants of the Sindar."
op. cit.

Then there is:
"The Elves far back in the Elder Days became divided into two main branches: the West-elves (the Eldar) and the East-elves. Of the latter kind were most of the elven-folk of Mirkwood and Lórien; but their languages do not appear in this history, in which all the Elvish names and words are of Eldarin form."
LotR, App. F

As Mithrellas was a Silvan Elf, and the Silvan Elves were apparently a mix of Avari and Eldar, Mithrellas would have been Avarin in origin.

An interesting aside:
Boromir and Faramir were both descended from Mithrellas as well, being the sons of Imrahil's sister.

[Jonathan]

That's interesting. Maybe Boromir and Faramir had more Elvish blood than Aragorn then

[Tuor of Gondolin]

Originally posted by Jonathan
________________________________________________Th e word 'Eldar' is applied to all elves, so if Tolkien said there were only three unions of the Eldar and Edain I guess he must've meant of all the Elves and all the Men.
________________________________________________
But there may be a "class" loophole for Mithrellas-Imrazor union, with Mithrellas being of the lesser Silvan race.

In Unfinished Tales (p.248)
"In the tradition of his house Angelimar was the twentieth in unbroken descent from galador, first Lord of Dol Amroth. According to the same traditions Galador was the son of Imrazor the Numenorean, who dwelt in Belfalas, and the Elven-lady Mithrellas......in this tale it is said that Imrazor harbored Mthrellas, and took her to wife. But when she had borne him a son, Galador, and a daughter, Gilmith, she slipped away by night and he saw her no more. But though Mthrellas was of the lesser Silvan race (and not of the High Elves or the Grey) it was ever after held that the house and kin of the Lords of Dol Amroth was noble by blood as they were fair in face and mind."

Granted this is only a "tradition", but combined with the observation of Legolas, it seems to present a strong case for at least a fourth union of human and elf. Could there then have been other "lesser" unions which weren't noted because not of high "royalty"? Remember, Tolkien was of a generally conservative disposition writing LOTR in a more class conscious first half of the twentieth century Britain.