This is a rich looking stitch, used especially to make flower petals. The weaving done to make this stitch gives a dimensional effect. It is a common stitch used in needle weaving style of embroidery and kamal kadai from India.

This stitch is done between three straight stitches.

woven_trellis_stitch_1         woven_trellis_stitch_2
Fig 1: Make three straight stitches of equal length, or with the middle stitch slightly longer. Try to give them a common centre point, as illustrated.   Fig 2: Bring the needle out from the common centre point. Start weaving by taking the needle under the first and last laid threads.
woven_trellis_stitch_3   woven_trellis_stitch_4
Fig 3: Then, turn around and this time, take the needle under the middle laid thread.   Fig 4: Repeat the process. Do not pluck the fabric underneath. The only time you take the needle through the fabric is when you start and when you end.
woven_trellis_stitch_5   Fig 5: A finished woven trellis would look like this. Since the middle stitch was a little too long, the top looks a bit clumped.