Quick Facts Oxalis triangularis, Scientific classification ...

Oxalis triangularis
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Oxalidales
Family:	Oxalidaceae
Genus:	Oxalis
Species:	O. triangularis
Binomial name
Oxalis triangularis A.St.-Hil.
Synonyms
Oxalis regnellii

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Oxalis triangularis, commonly called false shamrock, is a species of perennial plant in the family Oxalidaceae. It is native to several countries in southern South America. This woodsorrel is typically grown as a houseplant but can be grown outside in USDA climate zones 8a–11, preferably in light shade.

The deep maroon leaves are trifoliate, like species in the clover genus Trifolium which are commonly called shamrock, hence the name “false shamrock”. The leaves fold down at night, when disturbed, and when in harsh sunlight. The white or pale pink five-petalled flowers also close at night.

Growing to 50 cm (20 in) tall and broad, the subspecies O. triangularis subsp. papilionacea, the purpleleaf false shamrock, is hardy in mild and coastal areas of Britain, down to −5 °C (23 °F), and has won the Royal Horticultural Society’s Award of Garden Merit.^[1] It is a perennial plant without aerial stem, formed by leaves borne by a long petiole emerging at the ground level of a tuberous rhizome (5 cm long, over 10 - 15 mm in diameter, fully covered with scales). The leaf is formed of three sessile leaflets, obtriangular to obovate-triangular, glabrous, arranged in the same plane perpendicular to the petiole.^[2]

The five densely haired sepals are 5 to 5.5 mm long, narrow and slightly reddish at the top. The five white petals are about 2 inches long and oblong-lanceolate. The stamens and the style are densely hairy. The limb of the wild species is green but purple cultivars have been selected for horticulture. The petiole, soft, whitish, is 15 to 25 cm long. Flowering takes place from spring to autumn.

The species is distributed in several countries of South America: Brazil, Bolivia, Argentina and Paraguay. It is a neophyte in the United States in the states of Florida and Louisiana. It is also widely found in East India abundantly in states like Nagaland and Manipur.

O. triangularis requires bright indirect sunlight supplemented with a cool indoor temperature of 15 °C (59 °F). It can tolerate higher indoor temperatures but will go into dormancy prematurely and/or begin to take on a "tired" appearance if temperatures exceed 27 °C (81 °F) for prolonged periods of time. It thrives in an average potting soil with good drainage.

Mature plants are cut back to the soil every 3–5 years in early summer or during the dormancy period. Young plants are cut back to the soil every year in early summer or during the dormancy period, until they reach maturity. Fearing frost, they are usually grown indoors. They are planted in soil rich in humus and well drained. They should be watered only when the topsoil looks dry. In winter, they should not be watered.^[3] The main difficulty in caring for frost-resistant oxalises is to prevent them from growing uncontrollably.^[4] The ripe fruit of the plant will crack, throwing away seeds over a considerable distance, so do not plant the oxalis close to vegetable beds. Oxalis need no fertilizer before flowering. Afterwards it can be fertilised with an appropriate fertiliser. Plants usually only need nitrogen whereas phosphorus, potassium and easily absorbed trace elements help them to flower long and beautifully.^[5] When growing in a flowerbed,^[6] it is also worth feeding oxalis during the flowering period with a small dose of a multi-component fertiliser.^[7]

The subspecies Oxalis triangularis subsp papilionacea has won the Royal Horticultural Society's Award of Garden Merit.^[8]

Oxalis triangularis grows from corms, propagated by division. Like other corms, it goes through regular dormancy periods; at the end of each period, the corms can be unearthed, offsets cut and replanted in appropriate soil, where they will grow into new plants.^[9]