I think this is of the genus Senecio which includes several weeds here (eg. Ragwort and Fire Weed) and many native species as well but I haven't been able to identify this one either way. It's flowers only appear in bright sun, closing in the late afternoon to reopen the next morning.

Update: Well its not Senecio sp. but, rather, Arctotheca calendula L. commonly known as Cape Weed here.