Green is everywhere on St. Patrick's Day. People of Irish heritage -- or those who claim it, even if only for a day -- are wearing it. Some are even drinking it in the form of dyed green beer.

And shamrocks are everywhere, even in pots in flower shops.

Yet -- here's a little known bit of shamrock trivia -- there isn't a plant actually called "shamrock." It's a loose term for a group of plants sporting three leaves per stem.

The plants you see labeled shamrock -- according to Sunset's New Western Garden Book -- are actually small potted plants of Medicago lupulina (hop clover, yellow trefoil, black medick), an annual plant; Oxalis acetosella (wood sorrel), a perennial; or Trifolium repens (white clover), also a perennial.

So how did they become "shamrocks?" For that you'll have to study the legends surrounding St. Patrick, a missionary to Ireland who died over 1,500 years ago. Which makes it difficult to really know from which plant he plucked the stem of three leaves he used to explain the doctrine of the Holy Trinity.

Historians believe shamrock -- a word generally translated to mean "little clover" -- likely refers to white clover (Trifolium repens). Though others claim the small hop clover (Medicago lupulina) as the true "shamrock." Both of these do best outdoors. If you want a shamrock houseplant, choose one of the many Oxalis.

All Oxalis have clover-shaped leaves, but their colors and growing habits diverge widely from there. Leaves can be shades of green, red, purple or a combination of these accented with white or silver gray. Some grow in neat compact clumps, others reach for the light and get leggy. Some have white or pale pink flowers, others bright purple blooms.

As a rule of thumb, Oxalis require direct sun, so put them in a bright, sunny window. Keep the soil barely moist, even letting them dry out a bit between waterings. Fertilize them only when actively growing.

They prefer it on the cool side, 50-60 degrees at night, 75 degrees or less during the day. Warmer temperatures will likely send them into dormancy.

When this happens, the leaves die back. Simply stop watering, let the soil dry out and put the pot in a cool, dark place for a month or two.

When new shoots appear, give it a drink, feed it some fertilizer, and enjoy your shamrock for another season.

* Loretto J. Hulse: 582-1513; lhulse@tricityherald.com