Thorn stitch is used to embroider branches. It is a couching stitch where a long laid stitch is couched with cross stitches.
A long base stitch is first made. Bring needle up at 1 and go down at 2. Come back up at 3.
Now we will stitch a cross stitch to couch the long straight stitch. Go above the laid stitch and then down, pick up a few strands of the fabric and come back up on the other side like shown below.
End the thorn by going down at 5.
Come back up at 6 and start the next thorn.