Nimloth was the White Tree which grew in the King's Court in Armenelos of Númenor. It was brought as a gift by the Eldar from Tol Eressëa, in the form of a seedling from Celeborn as a symbol of friendship between the two races. Its blossoms appeared as the Sun set, and their perfume filled the night in Númenor's royal city.
However, the night before Isildur stole a fruit from the tree and when he escaped the Downfall of Númenor he took it with him towards Middle-earth. The fruit grew into a seedling that Isildur carried to Middle-earth with him during the Downfall of Númenor. That seedling was planted in Minas Ithil, and was destroyed before the end of the Second Age. Its seedling in turn grew into the first White Tree of Minas Tirith.