Folke Ohlsson - Made in Sweden  

@treehouse. It is Model 42. Have an image saved from Instagram, posted  by a reputable source. This is one of the earlier models and any catalogues etc I have seen say his earlier designs were offered in Teak or Oak. Later designs (60's), especially for the American market, were available in Mahogany and Walnut.

Thanks @lexi

Where I get stuck is that there are some subtle differences across chairs. For example a lower cross bar between the front legs, and sometimes beveling of the back top bar where it meets the vertical side pieces (such as seen in this one: https://www.midmodcrisis.com/dux-slat-back-chair.html). Mine doesn’t have the cross bar or the beveling, but does have the tell-tale webbing brackets that Ohlsson often used (when not using fagas straps). 
I imagine that these subtle differences could be different versions that were developed in different geographical locations or time periods. I just saw the chair today in an Illums Bolighus catalog listed on eBay, with the lower front bar, but sadly the seller said that the designer and model information is not listed in the catalog, and I can only make out the word “teak” (page 11, picture 6,  link here). 

@treehouse.  posting the advert. No lower bar. No close -up image to show if there is a "bevelled "  connection on back cross bar.  Not the best image  I have to admit!

As you say there may have been different versions of the chairs over time.

@lexi - This is great, thanks so much! 
I coincidentally have just recently run across Andreas Siesing’s book, Svenska möbler. It is out of print so I’m searching for a copy now. Thanks! 

It could also be that there is a lot of confusion with the Shield Company of California chair which is probably what that chair you linked to is. Notice the corner supports, those are mostly an American thing and the end of the legs are fatter on the Dux chairs. I have had several of these including ones that still had the Shield Company stickers still on them. I believe they were all made of ash like these and simply stained differently.

Here is a page from Furniture Forum 1953. The arm lounge chair is model 42, the slipper chair is 41, and the accompanying ottoman is 51. Consistent with early Dux, the wood is beech, with an option of stained/lacquered finish.

Interestingly, this page uses not only the same photos that lexi posted, but apparently they kept the formatting of the three chairs relative to each other the same as well. . . and a bird hanging out on the bottom backrest cushion.