Plant of the Week: Shamrock (Purple-leafed Oxalis, 'Rubra Alba')1

The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in "Plant of the Week." Please consult your local Extension office for plants suitable for your region.

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Plant of the Week

Purple-Leafed Oxalis, Shamrock, 'Rubra-alba'
Latin: Oxalis regnellii

It’s become increasingly common in recent years to use plants conventionally grown as houseplants as a part of the summer border. Sometimes these plants surprise us and prove more winter hardy than is generally believed, as is the case of the purple leafed oxalis. It is these never-ending little surprises that keep even the most experienced gardener interested in the fascinating hobby.

Oxalis are widespread throughout the world, with over 850 recognized species. All of these plants, which belong to the oxalis family, are lilliputian in size and are easily overlooked. One species, O. corniculata, the creeping wood sorrel, is a common weed of lawns and greenhouses and most people become first acquainted with the group through this pestiferous weed.

Purple-leafed oxalis produces 6-inch long petioles from the ground that are topped with a cluster of three deltoid shaped leaflets about an inch and a half long. The leaflets fold at the mid-vein and look like purple butterflies. The leaves are deep purple-black around the outer margin, with the inner portion maroon-purple. The presence of purple pigmentation is common in oxalis leaves. Green- and purple-leafed forms are common for many species. Most of the species are more maroon than purple, but this plant is decidedly Concord-grape purple.

If you dig up one of these plants you will find an odd looking root system that looks like a cross between a zipper and a centipede. This structure is the rhizome, or underground stem, that allows the plant to overwinter. It has overwintered successfully in Fayetteville for about four years now, but just how much cold it will actually tolerate is unknown.

The flowers appear in greatest abundance in the spring and sporadically throughout the growing season. Flowers are an inch long, white, five-petaled trumpets in a loose terminal cluster that tend to flop about. This species is native to Argentina, Bolivia and Paraguay and seems to have been cultivated in this country since the 1930s. There is no known record of where the purple-leafed form came from.

Purple-leafed oxalis can be used in sunny or shaded locations in the garden, but in deep shade the plant is so dark it just disappears into the gloom. It does best in fertile soil with a good supply of summer moisture. Its diminutive size makes it best suited as a front of the border plant or for edging beds of plants with a contrasting color, such as New Gold Lantana. It is also good for use in the rock garden where it will slowly spread and occupy crevices between rocks.

By: Gerald Klingaman, retired
Extension Horticulturist - Ornamentals
Extension News - July 28, 2000

 

The University of Arkansas System Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.