Hi Robin and thanks for your posting! I call it the SOS book too!
Tapioca flour, also called Yucca flour, is a flour made from the tuberous root of a plant called Manihot esculenta, which is native to Central and Southern America. The plant is a woody shrub that is more commonly known as manioc, cassava, and of course yucca (also sometimes spelled ‘yuca’).
In addition to being the source of yucca flour, the root is also used to produce tapioca. Tapioca flour helps to lighten gluten-free baked goods. It adds a slightly sweet flavor. This flour is used often in combination with other gluten-free flours in mixes. This is a powdered starch and its properties are similar to arrowroot.
You can purchase yucca flour in a natural food market. It may also be labeled tapioca flour, polvilho, manioc flour, or cassava flour. Bob’s Red Mill sells it as a gluten-free product with the label “Tapioca Flour.”
While tapioca flour is fine, the thing is I've rarely seen any GF products made only with this ingredient. It is usually combined with other GF products that are more processed, like rice flour (typically from white rice unless labeled as brown rice flour) and potato starch.