Oxalis purpurea
L.

Family : Oxalidaceae
Common names : grand duchess sorrel (Eng.); suring (Afr.)

Pink Oxalis purpurea

A common but undervalued South African native plant, Oxalis purpurea can make a most magnificent garden plant that flowers for half the year.

Description
Oxalis purpurea is a summer-deciduous winter-growing dwarf geophyte seldom higher than 6 or 7 cm. It forms a small rosette or mound up to 20 cm in diameter of trifoliate (clover-like) leaves which are dark green and not visibly hairy. It is unique amongst dicotyledonous plants in that it forms true bulbs which are often buried deep underground. Each bulb produces a single thin underground stem which gives rise to the above-ground rosette. The bulbs readily proliferate by producing smaller bulbils, each also producing a single stem, often resulting in a posy of plants and flowers in one place. The new shoots emerge from dormant bulbs after the first good autumn rains and will usually stay active until early summer (November in SA) but will go prematurely dormant if water becomes limiting. The flowers usually appear more than one at a time and when flowering en masse are spectacular. Each flower has five petals which flare like a trumpet during the day and furl at night or on overcast days. Flowers are usually pinky mauve to lilac and can be very dark and intensely coloured or very pale. Other less common colour forms include salmon, peach and pure white (albino). Flowers always have a yellow throat. Flowers start to appear from early winter (May in SA) and will usually keep flowering until the plants go dormant. The fruit is small (size of a match head) and contains many tiny seeds which are dispersed by explosive dehiscence.

Salmon coloured Oxalis purpurea
Pink coloured Oxalis purpurea

Conservation status
This plant is not currently threatened.

Distribution and habitat
Oxalis purpurea occurs naturally throughout the winter rainfall parts of South Africa, more specifically from Namaqualand in the northwest to Port Elizabeth in the southeast (Manning & Goldblatt 2000). It is an opportunistic plant that enjoys open soil, space and sunlight and therefore tends to proliferate in disturbed areas like along the edges of paths and roads. It is most commonly found in lawns where its low-growing prostrate habit is well suited to avoiding lawnmower blades! It is most spectacular after fires and is usually one of the first bulbs to bring colour to barren scorched earth in midwinter. It is suspected that the smoke also stimulates better flowering.

Derivation of name and historical aspects
The genus Oxalis was established by Linnaeus in 1753. The name Oxalis originates from the Greek word oxys meaning sharp, acid, sour, referring to the acidic nature of the plants as they contain oxalic acid. The specific epithet purpurea refers to the “purple” or mauve colour of the flowers. The genus occurs worldwide and most of the 800 species are found in South America. In South Africa the majority of the 200 species occur in the winter rainfall region of the Northern and Western Cape provinces (Du Plessis & Duncan 1989).

Ecology
The flowers of Oxalis purpurea are pollinated predominantly by bees and other generalist pollinators. The bulbs are often eaten by certain mole species.

Uses and cultural aspects
Because of the toxic oxalic acid these plants are seldom used as a food source, however, the bulbs of a number of species are eaten traditionally in South Africa but only after they have been dried or roasted (Du Plessis & Duncan 1989).

Growing Oxalis purpurea

Oxalis purpurea growing at KirstenboschOxalis purpurea makes a magnificent garden plant in winter and spring. It creates a spectacular splash of bright colour at an otherwise dull time of the year. Although this plant often occurs commonly in lawns (not to be confused with clover weed Trifolium pretense) it can be planted in open beds or in rockeries or even in between paving stones in a driveway or path. They are tough and will survive quite happily without any additional water in a winter rainfall area. A regular lawn can be transformed into a dazzling carpet of pink and mauve with minimal effort.

Sadly, these gorgeous little plants are often thought of as weeds and some people actively weed them out of their garden or tragically spray them with herbicides! Yes, there are a few exotic species (creeping sorrel O. corniculata from North America and O. latifolia – red garden sorrel from Mexico) which have become weedy in South Africa, but our own Oxalis species should be encouraged and can make superb low-maintenance garden plants. Amongst the various species suitable for cultivation, there is almost no end to the kaleidoscope of colours available, ranging from red, bright shocking pink, purple, orange, lavender, mauve, pale pink, cream, salmon, peach and pure white.

Plants are most easily propagated by bulbs and bulbils which can be harvested from the ground as the plants go dormant (as the leaves turn yellow) in early summer. Keep the bulbs in a dry cool place over summer and plant them in a pot or in the ground in early autumn. They make excellent pot plants where the bulbs will proliferate on their own over the years. They have no special soil requirements and will grow in sandy soils or in clay soils. The higher the humic content of the soil the more lush and prolifically the plants will grow. They flower optimally in a full sun position but can take some shade. Remember, the flowers only open in the sunshine. Fertiliser is not required but plants will flourish should it be applied.

Oxalis species being dicotyledonous plants do readily grow from cuttings, so don't be disheartened if you can't locate the bulbs which are often deep down in the soil; every little piece of stem will root, provided they are kept moist and cool for the first 2–3 weeks. Thereafter each cutting will start to form its own adventitious roots and bulb.

Seed is tricky to harvest when it is ripe as the capsules explode and expel their seed in all directions. They germinate readily in a sandy soil mix sown in autumn but plants will take a few years to mature to flowering stage. This option is therefore not recommended.

Apart from predation by the occasional mole, they rarely succumb to any damage from garden pests.

References and further reading

  • Bayer, B. 2000. In P. Goldblatt & J. Manning, Cape plants: a conspectus of the Cape Flora of South Africa.  Strelitzia  9: 552–560. Natonal Botanical Institute, Pretoria.
  • Dreyer, L.L. & Makwarela, A.M. 2000. Oxalidaceae. In O.A. Leistner (ed.), Seed plants of southern Africa: families and genera.  Strelitzia  10: 432, 433. National Botanical Institute, Pretoria.
  • Du Plessis, N. & Duncan, G. 1989.  Bulbous plants of southern Africa: a guide to their cultivation and propagation. Tafelberg, Cape Town.Retief, E. 2004. The genus Oxalis. www.Plantzafrica.com

 

 

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Kirstenbosch National Botanical Garden
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This page forms part of the South African National Biodiversity Institute's plant information website www.plantzafrica.com.


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