1 litre sized pot.  A chance seedling, Achillea millefolium Perfect Pink is a heat tolerant hardy perennial with fern like grey-green foliage and 40-60cm high flower stems topped with clusters of tiny pink flowers.  Needs a sunny position.  Achillea will wander a little in the garden but not overtaking other plants, they seem happy to share the space, great space fillers.  Popular with bees and beneficial insects and a great cut flower.