Yellow Wood Sorrel
- Lat. synonym: Oxalis corniculata
- Name also: Creeping Wood Sorrel, Procumbent Yellow-sorrel
- Family: Wood Sorrel Family – Oxalidaceae
- Growing form: Perennial herb. Rhizome thin.
- Height: 10–35 cm (4–14 in.). Stem ascending–erect, fuzzy-haired.
- Flower: Regular (actinomorphic). Petals 5, pale yellow, approx. 15 mm (0.6 in.) long. Sepals 5, blunt–sharp-tipped, hairy tip. Stamens 10. Pistils 5. Inflorescence a 1–7-flowered umbel.
- Leaves: Alternate, long-stalked. Blade trifoliolate, green–reddish brown. Leaflets triangularly obovate, with notched tip.
- Fruit: Cylindrical, 5-edged, 8–12 mm (0.32–0.48 in.) long capsule.
- Habitat: Gardens, parks, graveyards, dumps, forest margins. Ornamental.
- Flowering time: July–September.
Genus Oxalis is the largest of the family and the only genus represented in Finland. Most species can be found in tropical and sub-tropical areas of the southern hemisphere, especially in the South American Andes and parts of Brazil and South Africa. Species have however travelled with people to new areas, and many of the weeds in the genus are very difficult to eradicate and are a real nuisance to farmers in warm climates. Many wood sorrels propagate themselves mainly vegetatively, which has blurred the line between species and caused a lot of confusion. Yellow wood sorrel is often presented in literature as common yellow oxalis, (O. stricta), which is a very similar-looking close relative, although it is rare and casual in Finland. Creeping wood sorrel is often regarded as a separate species, but according to The Plant List yellow wood sorrel and creeping wood sorrel are the same species. In Finland yellow wood sorrel can be mistaken for common wood sorrel (O. acetosella).
Yellow-flowered yellow wood sorrel grows in the temperate zones of North America and eastern Asia in similar habitats as its Finnish relative wood sorrel. The species seems to be making its self at home in shady gardens and graveyards around trees and bushes. A red-leaved variety (var. ‘Rufa’) has probably been first introduced into flower beds, where it is an admired and impressive ornamental.