This is a variant of twisted chain stitch, but it looks a bit like an extra-fat stem stitch and is usually used in the same way. this stitch was truly new to me and it took a few trials to get used to. At the beginning of my sample, I just did lines of the stitch in all threads I had spontaneously availiable. Then I stitched the little twig and leaf motif, where I used this stitch as a line stitch for the twig and a fillig stitch for the upper part of the leaf. Sorry the motif is not perfect, I did not draw it beforehand.
I enjoyed this stitch, especially as a line stitch. As a filling stitch, I found it hard to keep even and well aligned wit previous rows. I think I prefer stem stitch for that, which gives a very similar look.