See Photo: The Lonely Tree Of Ténéré Is The Most Isolated Tree On Earth.

L'Arbre du Ténéré, known in English as the Tree of Ténéré, was a solitary acacia, of either Acacia raddiana or Acacia tortilis, that was once considered the most isolated tree on Earth— the only one for over 400 kilometres (250 mi). 

It was a landmark on caravan routes through the Ténéré region of the Sahara in northeast Niger — so well known that it and the Arbre Perdu or 'Lost Tree' to the north are the only trees to be shown on a map at a scale of 1:4,000,000. The Tree of Ténéré was located near a 40-metre (131 feet)-deep well. It was knocked down by a drunk truck driver in 1973.