Asëa Aranion

From the land of the Númenóreans, a herb of magical healing powers came to Middle-earth. In the High Elven tongue this herb was named Asëa Aranion, the "leaf of kings", because of the special powers that it possessed in the hands of the kings of Númenórë. More commonly, Elven-lore used the Sindarin name, Athelas; in the common Westron tongue of men it was Kingsfoil.

Rescue of Gondor
Among the many tales in the "Red Book of Westmarch" is recorded a art of the Grey-elven rhyme concerning the healing herb "Athelas". The meaning of the rhyme had in the passing of Ages been lost to the understanding of all but the wisest of Men, though by the time of the War of the Ring it remained a folk cure for mild ailments of the body.

In the terrible days of that war Aragorn, son of Arathorn, who was the true descendant of the kings of Númenórë from where the magical woodland herb had come, came to the kingdom of Gondor. It is told in tales that Aragorn, who had the healing herbs of these kings, broke the long-leafed herb into cauldrons of steaming water and released its true power. The fragrance of orchards, the coolness of mountain snow, and the light of a shattered Star poured into the dark rooms where the victims of poisoned wounds and black sorcery lay, until they stirred again with life and youth, and the long trace that had held them in sway broke before it had taken them to an evil death.

So Athelas was named Kingsfoil, the "leaf of kings", by Men and its use by a true king of Númenórë was a sign of the end that would soon come to that greatest evil of Mordor, east of Gondor, which threatened all who inhabited Middle-earth.