Oxalis tenuifolia Jacq.

A bulbous perennial with erect, slender stems with dense rosettes of leaves in the upper part, each leaf composed of 3 leaflets, somewhat folded and with a rolled edge, and solitary purple to white flowers, to 3cm across, with purple margins and yellow throats, in winter.  [RHSD].  

Horticultural & Botanical History

‘This is a native of the Cape of Good Hope, the neighbourhood of which is celebrated for numerous sorts of this pretty genus. […] The blossoms rarely expand, but continue shut up, in which state, from the fine striped colour of their outsides, they are most beautiful.’  [LBC no.712/1823].

Oxalis tenuifolia was introduced to Britain in 1790 [JD] but this plant is probably Oxalis versicolor L.

Hortus Camdenensis | Oxalis tenuifolia Jacq.