Well actually this is not a stitch in itself, but a combination. The edge of the petal is made up of #232 Romanian Macrame (Flower) Stitch, which we learned last week. I like that part very much. Using that linear stitch on a curve is OK on plain weave fabric, but it looks horrid on Aida, as you will see below.
Stretching the warp stitches must be done with care or they will either sag or pull the fabric too tight. I was also reminded that to make nice weaving you need an even number of warp threads, 6, 8, 10, 12 etc and not 7 or 9!
However, you can weave in different ways, over and under the warp. Another way of 'weaving' is of course whipping each of the warp. Then you get a bulkier look.
See how pretty the straight line of Romanian Macrame (Flower) Stitch (top of picture) is compared to the curvy one used as the edge of the petal. Aida is NOT always an easy weave to work on!
Sunday Stitch School Reference Chart