The message is correct. You need to install tk with the +x11 variant by running:
sudo port install tk +x11
Quartz is not X11. Quartz refers to the native windowing system of OS X, as opposed to the X or X11 windowing system common to UNIX systems.
You're probably thinking of XQuartz, the unfortunately confusing name for an X11 distribution for OS X. The name is probably meant to convey "X running on Quartz". MacPorts does not require XQuartz. MacPorts includes ports that have the same software as XQuartz.