alt Hacker Newsthe research is relevant to the issue of transpiration column hieght as a postulated limitation to overall hieght of any tree.
a column of water is pulled by hydrogen bonding between molecules in a tug of war fashion, the top of the column is where water is dissociated from the column at such a rate as to maintain low pressure with respect to the column[xylem]
in summary water moves from bottom to top in a transpiration stream, that ultimately ejects water vapour from the leaves, resulting in a low efficiency mechanism, that loses a lot of the water but occurs at such a rate that the low efficiency is "good enough" for whats needed.
> a transpiration stream, that ultimately ejects water vapour from the leaves
I don't believe this is correct, or rather is not a required component of the system but rather incidental. The chemical system within the leaf removes water via chemical reaction. There is a respiration process to dispose of waste gasses. Water vapor happens to be lost to this process not of necessity but rather because keeping it separate is quite difficult (ie requires significant complexity and additional energy expenditure). I expect that many desert adapted species approach perfection (but have not bothered to verify).