This question looks a little bit silly but I recently downloaded Ardour for OS X (Release 2.7.1) and installed it. I spent a lot of time trying to find a way to open a MIDI track (as well as the piano roll) in Ardour. Is this feature really available ? Looking at the screenshots, it seems so, but…
Midi tracks will be a feature of Ardour 3.x when it is released. Ardour 2.x does not have Midi tracks. If you have seen a screenshot then it must be of a development version of Ardour 3.x.