Silver Tree

Before his escape from the Downfall of Númenor, Isildur had rescued a fruit of the White Tree Nimloth, which was descended from Telperion of the Two Trees. From that fruit grew a seedling in the courts of Minas Ithil, and from that line came further generations of White Trees that graced the courts of Minas Anor (and Minas Tirith, after its renaming). From these came the emblem of the Royal House of Gondor, a Silver Tree on a black field.

Eärnur, the last King of Gondor, was lost in III 2050, and the time of the Ruling Stewards began. During their rule, the royal banner with its Silver Tree was replaced by the plain white flag of the Stewards, flying on the peak of the White Tower. The White Tree itself, growing in the courts beneath the Tower, survived for nearly nine hundred years after this, but in III 2872 it died, leaving no known seedling. By the time of the War of the Ring, it had been nearly 150 years since the Silver Tree - either real or flying on a banner - had been seen in the Citadel of Gondor, hence Aragorn's lament quoted above.

It would be Aragorn himself who restored the Silver Tree after the downfall of Sauron. He not only re-established the line of the Kings of Gondor, but with Gandalf's aid he found a seedling in a hallow of Mindolluin, so there was a White Tree growing once again in the courts beneath the Tower of Ecthelion, while the banner of the Silver Tree flew once again from its pinnacle.