That is probably my most close-up photo so far. In front of my Vivitar 90mm lens (which gets a macro ratio of about 1:2 on its own) I held my 18-55mm kit lens, set to 18mm and reversed, with the aperture release lever held open. Focusing was done by moving back and forward and the resulting picture was rather dark (the one above has been post-processed to bring out the colours).
However, that is impressively close. I think I may be able to use my camera gear to further my botanical studies; I wonder if I can get close enough to pick out individual cells?