This is a herbaceous perennial that grows quite well in Sydney gardens. It originated in Europe and belongs to the Caryophyllaceae family. It has soft basal leaves and in mid to late spring it sends up spires of delightful notched-edged, clear pink blooms (ht 60cm). It enjoys sun and well-drained, reasonably moist soil. The clumps may be periodically divided to increase the plants. It can be seen growing wild along the sides of the roads in England, where it is known as red campion or ragged robin. To me is a quintessential English cottage garden plant. Its rounded flowers provide a good contrast to the spires of Salvia, which begin their long blooming period in late spring.
Postscript: though I still see this plant growing well in the garden of some of my friends in Sydney, my own plant succumbed to being overcrowded by other plants.
Flowers in October, November.