OXALIDACEAE Oxalis regnellii ‘Purpurea’, Purple Oxalis/ Purple Shamrock/Shamrock
ox – al – is reg – nel – ee - i
Description: Mounding, rhizomatous perennial grown for its trifoliate leaves which may be green or purple.
Origin: South America.
Height x width: 1 foot tall and 1.5 feet wide.
Growth habit: Mounding.
Foliage: The 1- to 2-inch wide shamrock (trifoliate) leaves, consisting of three deltoid-shaped leaflets on 3-inch petioles, make a nice background for the plant’s delicate light pink flowers. Leaves are open during the day and fold up at night (“nyctinastic movement”) at the mid-vein. These movements have been variously attributed to a reduction of surface area exposed to cool night air to reduce heat loss, a reduction in the amount of moonlight absorbed to prevent false photoperiodic responses, or allowing light during the morning and late afternoon (the red/far red shift) to reach otherwise shaded leaf axils where the red/far red shift induces flower initiation.
Flowers: Delicate light pink or white flowers borne on long, slender stems.
Culture: Partial to full shade and moist, well-drained soil. Does not perform well in full sun during the hot summer.
Uses: O. regnellii, often used as a gift plant for St. Patrick’s Day, is a great plant for containers. Shamrocks are rhizomatous bulbs and require a dormant period occasionally. When they lose their leaves, restrict all watering and let the leaves die back naturally. Do not remove leaves until they are brown. Let the bulbs stay dormant for 3 to 4 weeks, then water and fertilize. In most indoor-grown shamrocks, the dormant period occurs two to three times a year.
Other facts of interest: References list purple Shamrock by a variety of names: Oxalis purpurea purpurata, O. regnellii atropurpurea, O. regnellii ‘Purpurea’, O. regnellii triangularis, O. triangularis. We have grown and overwintered O. regnellii successfully in a shady garden on the campus of Missouri State University which is in Zone 6, but some references claim the plant is hardy only in Zone 7 and above.
Related species: O. regnellii ‘Alba’ has green foliage.