From A Wiki of Ice and Fire
Black-barked trees are found near the House of the Undying, the seat of the warlocks of Qarth. Shade of the evening is made from the trees' inky blue leaves. The local name of the tree is not mentioned, and it is unknown if there is a connection with ebony of the Summer Isles, the ironwoods of Westeros, or the nightwoods of Essos.
A Clash of Kings
Daenerys Targaryen observes the ruins of the House of the Undying coiling through a grove of black-barked trees, and she finds it darker than expected when she walks among the trees.
- ↑ 1.0 1.1 A Clash of Kings, Chapter 48, Daenerys IV.