Native to South America, Oxalis triangularis takes its species name from the triangular shape of its leaflets, which range from green to variegated to a deep, rich maroon depending on the cultivar. The leaves are unmistakably shamrock-shaped, and they close when disturbed or as darkness falls, a movement visible enough to be entertaining. White to pale pink five-petaled flowers bloom in clusters on stems held above the foliage from spring into summer, attracting butterflies in the garden. In zones 8 and above it grows outdoors as a groundcover or border accent, going dormant in winter and returning in spring.

In cooler climates, Purple Shamrock thrives as a container plant or houseplant given loamy, well-draining potting mix and full sun to partial shade. If it goes dormant in autumn or during summer heat, reduce watering and wait — new growth will emerge within weeks. The unusual elongated rhizomes, covered in scale leaves that store water and nutrients, can be divided to propagate new plants. It is deer resistant and largely free of serious pest or disease problems.