Perennial plants with clover-like leaves are most likely members of the oxalis genus (Oxalis spp.), which is very large, containing about 700 species, most of which are perennial. Oxalis plants, sometimes known as sorrel or shamrock, grow from fibrous roots, tubers or rhizomes. Popular plants in the genus feature the characteristic deeply lobed leaves and rounded, five-petaled flowers that emerge from tightly furled buds. Depending on the species and variety, some oxalis are hardy in cold weather climates, while others cannot survive freezing weather and should be grown as houseplants.
Among the best-known perennial oxalis are wood sorrel (Oxalis purpurea), hardy in U.S. Department of Agriculture plant hardiness zones 9 and 10 and grown as houseplants elsewhere. Bearing pink, purple or white flowers in early to mid-summer, the plants also feature green, clover-like leaves that are creased in the middle and purple underneath. The plants grow to 6 inches tall, prefer full sun to part shade and are suitable for containers and edgings. Bowles variety (Oxalis purpurea var bowlesii), hardy in USDA zones 8 through 10, grows taller, reaching 12 inches. The flowers are pink-purple.
Native to parts of the United States, violet wood sorrel (Oxalis violacea), hardy in USDA zones 5 through 9, features three-lobed leaves that have a sour taste. Sprouting from bulbs, the plants spread via runners and can form colonies when planted in sunny to lightly shaded spots. The flowers, which range from white through pink and purple, appear in mid-spring, with an occasional bloom appearing in fall. Each violet wood sorrel bears three heart-shaped leaves that are creased in the middle. The plants top out at 9 inches, with an equal spread.
Some perennial oxalis species make excellent edging plants, especially for informal gardens within their hardiness zones. These include the depressa species (Oxalis depressa or Oxalis inops), hardy in USDA zones 7 through 10 and featuring showy, swirling rose-pink flowers in summer. The plants, which grow only 2 inches tall, with a 3- to 4-inch spread, require full sun and a sheltered location. Little strawberry oxalis cultivars like "Rosea" (Oxalis crassipes "Rosea"), hardy in USDA zones 5 through 9, according to Washington State University, are clump-forming plants, with heart-shaped, creased green leaves and small pink flowers.
Showy, perennial purple-leafed oxalis varieties are often sold around St. Patrick's Day. Among these are varieties of false shamrock (Oxalis regnellii). Authorities offer different opinions of the plant's hardiness, giving a range of USDA zones 6 or 7 through at least zone 9 or 10. The leaves are triangular, in groups of three, and the flowers are pink. False shamrock grows to at least 10 inches tall. Hybrids may be taller still. Another large, purple-leafed type is fire fern (Oxalis hedysaroides), hardy in USDA zones 9 through 10, which produces yellow flowers and grows up to 3 feet tall.
- Christian Science Monitor: Oxalis -- A Great Plant Indoors and Out
- The Botanical Garden, V 2, Perennials and Annuals; Roger Phillips and Martyn Rix
- The American Horticultural Society Encyclopedia of Plants and Flowers; Christopher Brickell, Editor-in-Chief
- Missouri Botanical Garden: Plant Finder -- Oxalis Purpurea
- Missouri Botanical Garden: Plant Finder -- Oxalis Violacae
- Perennials.com: Oxalis crassipes "Rosea"
- University of Oklahoma Department of Microbiology and Plant Biology: Plant of the Week - Oxalis Regnellii Atropurpurea-
- Hortus Third; Liberty Hyde Bailey, Ethel Zoe Bailey, et al.
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