Guardian: Wangari Maathai’s office in fuming, downtown Nairobi is full of citations and mementos, but there is one special photograph. It’s of her and Barack Obama planting an olive tree in Uhuru park in the city centre in October 2006. It could be any two celebrities posing for a routine photo call, but there is a strong connection between the spiffy, young American senator on his way to the White House and the flamboyant older woman dressed in canary yellow who had just become the first African …