At first glance this skirt simply looked like a nice early 1950s straight skirt in a lovely color and with an interesting button placement. But then I noticed the belt. It was a golf tee holder.
By that time the seller was starting to unbutton the skirt, which is not a skirt at all.
It is actually a culotte or divided skirt, but it is cleverly disguised by the stitched pleats. The back is also stitched, and it just looks like an inverted pleat.
This was not a new idea in the 1950s. Before it was acceptable for women to wear trousers, there were all kinds of ingenious ways to make a skirt have two legs. I have an example from the 1910s in my collection, and it is quite similar to this 1950s culotte skirt.
I really don’t know a thing about Sporteens, except that the listings that I’ve found of items for sale with the label are overwhelmingly skirts. I also found a 1944 ad for a jacket and matching skirt.
And here is a very similar one, but without the buttons, from California sportswear designer De De Johnson, 1952
The Vintage Traveler 