Top o' the morning' to you!

Today is the day for the wearin' o' the green - St. Patrick's Day, celebrated with parades, Irish jigs, greendyed carnations and the shamrock, a dainty green plant sold by florists and on street corners on Mar. 17.

Just what is this little green plant, the shamrock?Beliefs about it vary. The word shamrock appears to have been adapted from an Irish word for clover. The plants sold as shamrock in the United States are usually "little white clover," Trifolium repens. The official Irish shamrock used in Dublin is "yellow clover," Trifolium dubium.

The characteristic three-parted leaves of clover are also common to the Oxalis genus and for this reason oxalis also is popular known as shamrock. In fact, there are devotees of the Irish tradition who belives that the true shamrock is a creeping Oxalis species. One of the shamrocks sold by florists is Oxalis braxiliensis, a bulbous plant with crimson flowers.

It was "the luck of the Irish" when I discovered Oxalis as a plant for the indoor garden. For that reason Oxalis is the subject of this St. Patrick's Day column.

A common name of Oxalis (pronounced OX-aliss or Ox-Alice) is wood sorrel. There are 300 different kinds, some with woody stems, some with edible tubers; some are delicate wild-flowers, and one is the common yellow-flowered weed (Oxalis corniculatus), which in my childhood we gingerly tasted and dubbed "sour grass."

The name Oxalis comes from the Greek for "sour." The leaves of some kinds are recommended for inclusion in green salad because of the sour juice, but all conatin oxalic acid and should be used with discretion as oxalic acid is toxic.

All have compound leaves of three or four leaflets; they are noted for folding their leaves (going to sleep) at night and on dark days, which makes them appealing to junior gardeners.

When considering this group of plants for the indoor garden it would be difficult for me to play favorites, for the Oxalis genus affords a choice between flower color and leaf color or form, continous or intermittent bloom, erect or hanging plants. They grow from bulbs, roots or tubers.

So I will share with you a few that I have liked, without any order of precedence. Five good bulbous types are:

Oxalis rosea, celebrated as "grandmother's favorite houseplant" in times gone by. Her success with this tuberous Oxalis was due to cool windowsills and high humidity form the tea kettle constantly on the stove.

Oxalis variablilis (or O. purpurea), known as "Grand Duchess;" it has huge clover leaves, lavender and white or rose flowers.

Oxalis braziliensis also has three-parted leaves (as do most), with crimson or wine-red flowers; it needs to rest after flowering.

Oxalis martiana aureo-retuculata comes from tropical America; its light green leaves are veined with gold (aureo); the flowers are rose with white throat; while it flowers intermittently, the colourful leaves, even though they tend to sprawl, are a bright feature among other foliage plants. This one can be used in a terrarium and is excellent in the light garden.

Oxalis regnellii produces larger parasol leaves, each section a triangle, green above and purplish beneath. It is a prolific bloomer, with sprays of white flowers standing erect above the leaves, making a total height of about 8 inches. The bulbs multiply quickly in the pot. If kept constantly moist, it will not go dormant as do some other bulbous types. My own plants flower continously either under fluorescent lights, in a sunny window or in a north window. It is hardy outdoors in this area.

For variety in type of plant, here are some fibrous-rooted kinds that I have found to be good housplants of uncommon interest.

Oxalis siliquosa, the "red velvet shamrock," is rather rambling or sprawling in the pot but it is easily propagated from the pieces removed when pruning to keep it within bounds. The small reddish clover leaves are held on yellowish stems. It is ever-blooming with yellow flowers and very usable in a small hanging pot. A good light garden subject.

Oxalis hedysaroides rubra, the "Fire Fern," is a shrubby type. It is said to grow 2 to 3 feet tall in its native Ecuador. Ten to 12 inches is probably as large as you will want to let it grow particularly if you have it under lights. Pinching creates a bushy specimen. If it grows too tall and leggy, cut the branches down to 3 or 4-inch stubs; the base will sprout and the cut pieces can be used to propagate new plants. The wiry stems and dainty deep red leaves of this species are graced with small flowers of intense yellow. It needs protection from hot sun. Incidentally, it is a "sensitive plant," folding its leaves when touched, and the leaves exhibit a peculiar up and down movement at any time of day rather than folding at night.

Oxalis ortgiesii, the "Tree Oxalis," is a fibrous-rooted plant about 12 to 18 inches tall. The red leaflets are described as "fishtail" in outline. The succulent erect stem may be maintained at desired height by pinching or by taking cuttings, which root readily. Flowers are yellow. Being succulent, it requires less water than regnellii or martiana, for instance. It does well in the light garden.

Oxalis herrerae, with an appearance of some of the true succulents, seems to me to be a collector's oddity - a plant for someone who enjoys confounding visitors by pointing to it and asking, "What kind of plant would you say that is?" It is ever-growing with yellow flowers. A strange Oxalis!

In the nursery lists you will find a number of other Oxalis species, all reputed to be easy to grow. Two that I am eager to try are:

Oxalis deppei, which has four-parted green leaves and is called the "Good Luck Plant" and "Lucky Clover." The flowers are rose-red. The bulb is edible and was once cultivated for food in Europe.

Oxalis pes-caprae is the "Bermuda Buttercup;" there are both double and single-flowered forms. Though troublesome as a spreader in Southern gardens, it should be good as an indoor plant. Its bulb, too, is edible, but I don't propose to test the palatability of either of these.

Outdoor gardeners will find that the lists include a number of species especially recommended for rock gardens.

All the Oxalis are of easy culture. They require a well-drained soil, slightly acid. I use a soilless mix of peat, perlite and vermiculite or commercial brands of sterilized potting soil with generous addition of perlite. With few exceptions, these plants perform well in a cool room (60 to 70 degrees) with bright light or sunlight.The soil should be kept moist. Liberal amounts of water are frequently required during flowering. Varieties of succulent nature such as O. ortgiesii and O. herrerae are less thirsty than the others.

Withhold water from the bulbous types when they have finished flowering; store the bulbs in their pots or in bags of peat moss.

Any balanced liquid houseplant fertilizer, such as Hyponex or Schultz, is suitable; occasionally switch to fish emulsion.

Propagation method depends upon the species. Separate the bulbs and report them; one bulb may be used per pot or, for a bigger show immediately, start with 6 bulbs in a 4-inche pot. Others, according to species, are increased by dividing the roots or by cuttings.

The species of Oxalis represent one of the most widely distributed and most clearly defined natural groups of flowering plants. Some of them appear in small numbers on all the continents.

Two areas in which a large percentage of the total are concentrated are a narrow coastal belt in South Africa and along the coast of South America from Peru to the end of the continent. All of the South African species form bulbs; many of the South Africans are herbs (nonwoody plants) of moderate size; several from South America are worthy of being called shrubs.

Whether you are an Irishman looking for a shamrock or not, I am sure you can find some intriguing additions to your indoor garden among this group of flowering plants.