Eucalyptus regnans

The mountain ash (Eucalyptus regnans) of southern Australia is the tallest of all flowering plants, and possibly the tallest of all plants. That claim is given credence by the documented fact that in the 1880s the State Surveyor of Victoria measured with a theodolite a mountain ash in Victoria at 114 metres (almost two metres taller than the world's current tallest living tree, a coast redwood); unfortunately that tree was promptly cut down and the stump commemorated with an insignificant plaque that exists today.