From Wikipedia: Oxalis pes-caprae (Bermuda buttercup, African wood-sorrel, Bermuda sorrel, Buttercup oxalis, Cape sorrel, English weed, Goat's-foot, Sourgrass, Soursob and Soursop; (Afrikaans: Suring) ) is a species of tristylous flowering plant in the wood sorrel family Oxalidaceae. Oxalis cernua is a less common synonym for this species.
The Oxalis pes-caprae flower is actinomorphic, with a calyx composed of five free or slightly fused sepals, a sympetalous corolla composed of five fused petals, an apoandrous androecium composed of ten free stamens in two ranks, and a compound pistil. Like most African Oxalis species, it produces adventitious subterranean propagules. These take the form of true bulbs in botanical terms, which is unusual among dicotyledons. In fact, Oxalis pes-caprae produces small bulbs copiously, whereas most other African species produce fewer, larger bulbs. New world Oxalis, such as Oxalis corniculata, apparently do not generally produce bulbs.
Indigenous to South Africa, Oxalis pes-caprae, the "Bermuda buttercup", is a highly invasive species and noxious weed in many other parts of the world, including the United States (particularly coastal California), Europe, Israel and Australia, and particularly our garden!
Soursob, home garden (alas), Adelaide, South Australia