Celtic Octagon

Foundation ring: Using A, ch 6, join with ss to form a ring. 
Round 1: [Ch 4, 3 tr into ring, ch 4, 1 ss into ring] 4 times. 
Fasten off A. Join B. 
Round 2: Ch 6 (counts as the first dc and ch 3), skip [ch-4 sp, 3 tr, ch-4 sp], *[1 dc, ch 3, 1 dc] into next ss, ch 3, skip [ch-4 sp, 3 tr, ch-4 sp]; rep from * twice more, 1 dc into last ss, ch 3, join with ss to third ch of beg ch-6. 
Round 3: Ch 5, *3 tr into ch-3 sp, ch 4, 1 sc in next dc, ch 4; rep from * 6 times more, 3 tr into ch-3 sp, ch 4, join with ss to the first ch of beg ch-5. 
Fasten off B. Join C. 
Round 4: Ch 5, *skip [ch-4 sp, 3 tr, ch-4 sp], 1 sc in next sc, ch 4; rep from * 6 times more, skip [ch-4 sp, 3 tr, ch-4 sp], join with ss to the first ch of beg ch-5. 
Round 5: Ch 3 (counts as first dc), *[2 dc, ch 3, 2 dc] into ch-4 sp st base of beg ch-3, 1 dc in next sc; rep from * 6 times more, [2 dc, ch 3, 2 dc] into ch-4 sp, join with ss to top of beg ch-3. 
Round 6: Ch 1, 1 sc into each of next 2 dc, *2 sc in ch-3 sp, ch 3, ss in last sc made, 1 sc in same ch-3 sp, 1 sc into each of next 5 dc; rep from * 6 times more, 2 sc in ch-3 sp, ch 3, ss in last sc made, 1 sc in same ch-3 sp, 1 sc in each of last 2 dc, join with ss to beg ch-1. 
Fasten off. 
Arrange petals of Round 3 in front of Round 4, and petals of Round 1 in front of Round 2.

Motif directions reproduced with permission from 150 Knit & Crochet Motifs, Interweave Press, 2011
Sample shown in Wool-Ease.