Phil Bendle Collection:Oxalis pes-caprae (Yellow sorrel)

Kingdom: Plantae 
Division: Magnoliophyta 
Class: Eudicotyledoneae 
Subclass: Rosidae
(Unranked): Eurosids 
Order: Oxalidales 
Family: Oxalidaceae 
Genus: Oxalis 
Species: Oxalis pes-caprae 
Synonym:  Oxalis cernua 
Common name: Yellow sorrel, Soursob, Bermuda buttercup, African wood-sorrel, Bermuda sorrel, Buttercup oxalis, Cape sorrel, English weed, Goat's-foot, Sourgrass, Soursop

Oxalis pes-caprae is a species of tristylous flowering plant in the wood sorrel family Oxalidaceae. Its 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 does not generally produce bulbs.
Oxalis pes-caprae is a weed of gardens, orchards, cereal crops and pastures and invades dry coastal vegetation, heathland and healthy woodland, lowland grassland and grassy woodland, dry sclerophyll forest and woodland, riparian vegetation and rock outcrop vegetation. 
This invasive species 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 New Zealand. The plant has a reputation for being very difficult to eliminate once it has spread over an area of land. The weed propagates largely through its underground bulbs and this is one reason why it is so difficult to eradicate, as pulling up the stems leaves the bulbs behind. The soil in which the plant has grown is generally filled with small bulbs. Another reason is that the seeds are tiny, hard, and sticky when ejected from the follicle. If they stick to an animal or vehicle, they may be carried far without detection. Oxalis spreads prolifically and is a real challenge to eradicate. The main problem is that you can pull out the weed but one leaves under the soil its parent bulb with a number of little bulblets attached to it.

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[2] The flowers closeup at night. Photographed early morning.
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[4]

Flowers just opening.

Thanks to Wikipedia for text and information:

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