Oxalis regnelli 'Triangularis' Purple Shamrock

Oxalis regnelli 'Triangularis' 
Purple Shamrock

Mention Oxalis and you immediately think of noxious garden weeds most of which have a Class 5 restriction attached to them. The main garden culprit is Oxalis corymbosa or Pink Shamrock which produces a large number of small bulbils attached to a central tuber.These bulbs spread far and wide and can be difficult to remove from garden beds. It is interesting to note however that the tuber which is carrot-like in shape and a translucent white. is edible and quite sweet to taste. A more cultivated form with a larger tuber(10cm) and of South American origin is Oxalis tuberosa or "Oca" which you are more likely to encounter at a vegetable market in La Paz or the Titicaca area of Bolivia and in Venuzuela where it is known locally as cuiba.

Oxalis regnelli is the kitten of the group and behaves itself very nicely. It does not set seed or bulbs and the tubers are very slow to increase. It is at its best in Summer when the leaves appear almost black which contrast well with the pale mauve flowers. As it spends quite a bit of time dormant it makes an ideal container plant and one which can be brought indoors at this time of year. It makes an appearance as such in the home of a New York art critic in the documentary film Black White + Grey (A portrait of Sam Wagstaff + Robert Mapplethorpe
2017 update: The leaves get a rust which can be quite disfiguring but cutting it back to ground level brings on a new flush of leaves.