In Fig. 56 is shwon a form of the acanthus leaf taken from the Tower of the Winds at Athens. it is purely conventional in form, possessing a broad, bold treatment, necessary or its execution in stone, and following closely the principles of the growing plant, as do all other developments in Greek ornament. (p. 65)
You could probably repeat this decorative leaf, perhaps interspersed with something circular for variety, to make a border.