This stitch consists of evenly-spaced small vertical anchoring stitches, interwoven with a diagonal trellis.  Most trellis stitches are worked with the long threads laid first and then anchored with small crossing stitches; this version is worked with the small anchoring stitches first which softens the lines of the trellis, making it slightly curved.

For a more angular version, see fly stitch filling.

Ukranian interlaced running stitch has one subtle difference: the diagonal interwoven threads stretch across the whole of the design area, rather than being worked row by row.  This results in a straighter trellis.

N.B. this stitch has been given a structure of ‘couched’ as visually it appears as if it were couched (although the order of working the anchoring stitches first means that strictly this isn’t correct).