Grete Jalk or something else?  

Again, I agree with Leif. It's either mahogany or one of the earlier mahogany substitutes. The last photo looks to me like the grain may be interlocked, which would indicate a species other than a "true" mahogany. But that's splitting hairs and hardly matters.

All right, gentlemen--what does that tell us about the chair's likely origin?
(I will add that I've taken the chair apart once, and don't believe that the existing hardware (screws to hold seat and back to frame) is original....)

I have some more info that may or may not be helpful to those with more knowledge than me. Here's a listing on 1st dibs:
https://www.1stdibs.com/furniture/seating/lounge-chairs/peter-hvidt-orla...
Note the general dimensions of the sled base, the slight protrusion of the two back pieces above the horizontal support, and the curved back support slats which appear identical to those on the Jalk? chair this thread concerns....

France and Søn/Daverkosen did not make these "Jalk" chairs. Charles France was extremely reliable about marking his products (maybe because he was English). So the similarity is merely superficial. Unfortunately.

ah well....thanks Leif! could those curved back support pieces that woody also noted be a kind of generic Danish part? I wonder...