Base rnd, each side: Multiple of 9 + 8 + corner sts.
Begin 3 sts to left of corner st.
Rnd 1: Ch 1, sc in same st, *ch 2, skip 2 sts, sc in next st, skip 2 sts, [5 dc in next st, skip 2 sts, sc in next st, ch 2, skip 2 sts, sc in next st, skip 2 sts] to corner st, 7 dc in corner st — corner group made, skip 2 sts, sc in next st; rep from * around, omitting last sc, join with slip st to first sc, slip st in next ch-1 space.
Rnd 2: Ch 1, sc in same space, *[ch 2, (dc in next dc, ch 1) four times, dc in next dc, ch 2, sc in next ch-2 space] to sc before corner group, ch 2, (dc in next dc, ch 1) six times, dc in next dc, ch 2, sc in next ch-2 space; rep from * around, omitting last sc, join with slip st to first sc. Fasten off.
Rnd 3: Join yarn in last dc of previous rnd, ch 2, skip (ch 2, sc, ch 2), dc in next dc, *[(ch 2, dc in next dc) three times, ch 2, Partial dc in next dc, skip (ch 2, sc, ch 2), Partial dc in next dc, yarn over and pull through all 3 loops on hook — dc2tog over 2 dc made] to corner group (placing last Partial dc in first st of corner group), (ch 2, dc in next dc) five times, ch 2, dc2tog over next 2 dc; rep from * around, omitting last dc2tog, join with slip st to first dc.
Rnd 4: Ch 1, *[(3 sc in next ch-2 space, Picot-3) three times, 3 sc in next ch-2 space] to dc2tog before corner group, (3 sc in next ch-2 space, Picot-3) five times, 3 sc in next ch-2 space; rep from * around, join with slip st to first sc. Fasten off.