Indigenous to South Africa, the 'Soursob',
Oxalis pes-caprae is an introduced noxious weed throughout all of Australia.
That being said I am particularly fond of soursobs as they bring back childhood memories of chewing on the acidic stalks and screwing up our faces from the intense sourness.
Another interesting aspect of the soursob flower is that they close up for the evening and open up again the next day in the sun.
Photo: Robert Rath, '366 Days of 2012, Day 266 - Sour Flower'. 1/640s f/4.0 ISO320 100mm macro