<<Disclaimer: Verify this information before applying it to your situation.>>

According to the Encyclopedia Brittanica, a source of general information
that I highly recommend to the readers of this list and one that can be
found in most local libraries, flax is a dicot with scientific name Linum
usitatissimum L., it belongs to the subclass Rosidae, order Linales, family
Linaceae.  The seeds are the source of linseed oil used in paints and
varnishes.  Linseed has been used as a food for humans and animals since
Greek and Roman times. The vegetative parts of the plant, mainly the stems,
are used for fiber.

I see no close relationship to wheat, rye, barley, or triticale, the grains
of concern to those with celiac disease, all of which are monocots rather
than dicots and all of which belong to the grass family--as do rice and
corn, grass species that are, however, not considered harmful to those with
celiac disease.

Don Kasarda
Albany, California