The Ténéré Tree was a solitary acacia (Vachellia tortilis) that was once considered the most isolated tree on Earth (the only one for over 150 kilometres). It was a landmark on caravan routes through the Ténéré region of the Sahara Desert in northeast Niger, so well known that it and the Arbre Perdu (Lost Tree) to the north are the only trees to be shown on a map at a scale of 1:4,000,000. It was knocked down in 1973 by a truck driver. [wiki]
The picture is from 1961.