The Oxalis are a big and varied family, from pernicious weeds to alpine treasures from Chile and colourful South African low landers. Oxais lobata is from Chile but I think from low altitudes. Bright green lush looking leaves and golden yellow flowers. It's supposed to be autumnal but I find it starts flowering late summer.
I now have a couple of large pots in the greenhouse and an escape in a trough. In the trough it is a bit neater, in the greenhouse the flower stems tend to draw a bit. It's survived in the trough for several years now but has only grown quite slowly.
In old books people are warned that this has an odd habit of having two dormancies, in the summer and the winter. Apparently people used to complain that the plant had died to the nurseries. Seeing as it wasn't exactly easy to get except from specialists even then I'm suprised a prospective buyer would be unaware of this. Having said that, for me it only dies back in summer, it remains in leaf from late August until the late spring.