This stitch is made of series of three straight stitches. It resembles a fern leaf and so, a good stitch to do vegetational designs.

You need to know how to do the straight stitch. I will work over three parallel curved stitch lines to bring out the effect.

fern_stitch_1      fern_stitch_2
Fig 1: Bring the needle out from A and take it in through B, both points which lie over the second stitch line.   Fig 2: Now, Take the needle out through C, a point which lies on the first stitch line.This point lies a little higher than the point B (about 45 degrees).
fern_stitch_3    fern_stitch_4
Fig 3: Now, take the needle in through the point B. Then, bring the needle out through point D, and take it in through B. 
This finishes a set of three straight stitches.
  Fig 4: Bring out through E and back in to B. Follow the illustration to continue.
 fern_stitch_5    Fig 5: A finished portion looks like this.