This is a common weedy Oxalis of gardens around the world. The only problem is I don't know its name.

The rather out-dated volume of Flora of the Sydney Region that I have gives two possibly names, O. corymbosa and O. latifolia, the difference being the leaves obcordate or roughly triangular. The plants in my garden seem to fit both categories.

Andrew Harvie (March 11, 2003)
Australia