According to the syndicated newspaper feature, “Did You Know?” …. In Ireland, the plant most identified as a ‘shamrock’ is the white clover.
However, according to Horticulture Magazine (March 2009 email), the shamrock houseplant is Oxalis regnellii.
It’s described as follows:
“Houseplant with shamrock-shaped bright green foliage and dainty white flowers on tall, delicate stems. Blooms in late winter/early spring.
Foliage: Triangular leaflets held in threes atop slender stems.
Flower: Five-petaled simple white flowers held in groups of five or six atop slender stems, rising just above foliage.
Habit: Dense with leaves on individual stems. Grows from a rhizome.
Origin: South America
Cultivation: Bright indirect light; some direct sun OK. Allow soil to dry slightly between waterings.
Fertilize with houseplant fertilizer in summer, and place plant in shady location outdoors. Leaves die down in fall; stop watering. Start again in early February to encourage the plant out of dormancy.”