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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
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