Height = (2.5 * size)em; Position = (pos * 2.5 - 2)em. This assumes that browsers lay out tables where line-height:100% is set with 2.5em per row, which tests show to be ok for those browsers I've tried. But what about old versions of IE?
The start bar on the following cladogram (where green marks the bryophytes) is perhaps a bit ugly. Note that this version of the cladeN template produces a double line for child N by simply specifying stateN = double.
embryophytes
liverworts
mosses
hornworts
polysporangiophytes
pre-tracheophytes
tracheophytes
Drawing the cladogram the other way round gives:
embryophytes
polysporangiophytes
tracheophytes
pre-tracheophytes
hornworts
mosses
liverworts
You can just omit the start and end bars and use an ordinary one, but an inherent feature of the way {{cladeN}} works makes the bar always to the right of the rightmost leaf: