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AUTHOR

David Trinklein
University of Missouri
Division of Plant Sciences
(573) 882-9631
trinkleind@missouri.edu

Oxalis: Shamrock's Imposter

David Trinklein
University of Missouri
(573) 882-9631
trinkleind@missouri.edu

Published: March 7, 2019

oxalis

In the year 432 AD., a missionary, who earlier assumed the name Patricius, arrived in Ireland with the objective of converting the Celtic Irish to Christianity. Legend has it that he used a three-leafed plant to illustrate the Christian doctrine of the Holy Trinity. Today, we refer to Patricius as St. Patrick and the three-leafed plant as a shamrock. Indeed, nothing is more symbolic of St. Patrick, St. Patrick's Day or the Irish as is the shamrock.

History does not record what plant St. Patrick used in his teachings. Most likely it was a clover, since the word shamrock is derived from the Irish word seamróg, or "little plant". Today, yellow clover (Trifolium dubium) is widely referred to as shamrock and, in honor of St. Patrick, has been used as an Irish symbol since the 18th century.

Irish shamrock (yellow clover) as well as a miniature form of white clover (Trifolium repens) are sometimes commercially available as novelty potted plants for St. Patrick's Day. However, another plant with three-parted leaves with a clover-like appearance also is sold as a shamrock. The plant is Oxalis, which constitutes a large genus of flowering plants in the wood-sorrel plant family.

While the true shamrocks are an interesting novelty plant for St. Patrick's Day, they are not well adapted to extended survival under interior conditions. They need very bright light and should be placed in a sunny, cool window. When temperatures are too high or too low, they tend to become thin and "leggy". Additionally, true Irish shamrock is an annual plant and, as such, not long- lived. Miniature white clover is a winter hardy perennial plant also poorly adapted to the indoor environment. However, if purchased as a novelty potted plant for St. Patrick's Day, it may be moved outdoors after the weather has warmed in the spring.

On the other hand, numerous species Oxalis are attractive houseplants that are much better adapted to interior conditions. Although oxalis foliage may look like that of a clover, this genus of plants originated far from Ireland. Most oxalis are native to the mountainous regions of South and Central America. They also require a bright, sunny window to thrive but are more tolerant of higher home temperatures than are the clovers.

While true shamrock has a fibrous root system, many oxalis species produce tubers, or bulb-like structures. In fact, the plump, juicy tubers of Oxalis tuberosa have long been cultivated as a food source in Colombia and other South American countries. Referred to as oca by people indigenous to the area, it is second only to potato in acreage planted in the Central Andean region.

Most of the oxalis species used as house plants (e.g. Oxalis versicolor) produce this type of bulb-like storage structure. Oxalis with this anatomy usually require a rest period after their main period of flowering is over. As the plants begin to weaken and look "poorly", allow them to dry down. Dead leaves should then be removed and the plant allowed to remain dormant and dry for four to eight weeks. Plants that continue to flower and grow should not be forced into a rest period, since they probably belong to an oxalis species that does not have a dormancy requirement.

At the end of the rest period, the bulb-like structures may be divided and repotted before forcing new growth. The latter normally will resume as soon as regular watering is begun.

Oxalis plants tend to be very durable that grow well in any good, porous potting medium. After potting, new plants should be kept in a sunny window. Spider mites can be quite damaging, therefore regular monitor for mite and insect infestation is advisable.

The clover-like leaves of oxalis are available in many interesting forms. One of these, Oxalis deppei, often is referred to as the Good Luck Plant or Lucky Clover. The latter two common names refer to the fact this species produces leaves with four leaflets instead of three. Thus, it is a reliable source of four-leaf clovers.

Another species, Oxalis triangularis, bears large, deep-purple leaves. An attractive houseplant, it also can be used outdoors as an annual bedding plant. As is the case with several species of this genus, the leaves of Oxalis triangularis exhibit the unique diurnal rhythm of opening during the day and closing (like an umbrella) at night. It bears white or pale pink flowers that also close at night.

Oxalis often is referred to as sour clover, because the leaves have a sour flavor when chewed. Our native yellow woodsorrel (Oxalis stricta) bears leaves, flowers and unripe fruits all having a sour, tart, lemony flavor. Considered to be edible, leaves of this species can be added to salads, soups, or sauces, or used as a seasoning. The mature seed pods of yellow woodsorrel open explosively when disturbed and can spread seeds up to 13 feet.

Most oxalis species bear attractive flowers. One species, Oxalis purpurea, native to South Africa bears very showy large, pink flowers and makes a very attractive garden plant. Other species may have white, yellow, rosy pink or multi-colored flowers.

Thus, if in the spirt of St. Patrick's Day you choose to purchase a shamrock, be advised it probably is oxalis, its imposter. The mislabeling probably was not intentional and, in the long run, will result in greater enjoyment of your purchase.

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REVISED: February 21, 2017