What kind of wood are wooden tongue depressors made of?

Northern white birch, because it is flexible, relatively splinter-free, and inexpensive.

Tongue depressor processing flow:

double segment rotary cutting machine,tri-carved cutting machine,stoving and polishing machine,tongue depressor chamfering machine,tongue depressor branding machine,tongue depressor selecting machine,bundling machine

Tongue depressors have myriads of other uses, such as page markers, straight edges for underlining journal text ( for those of us who eschew medical literature on the computer), children's puppets, plant markers in the garden or in seed starter kits, and for spreading peanut butter on crackers in the office kitchenette. Certain illiterati have been known to stir coffee with tongue depressors, but a true connoisseur such as myself knows that they impart a bitter taste to the brew.