Oxalis corniculata

Morphological description

Perennial herbaceous plant, small in size, with height generally ranging between 5 and 30 cm, characterized by a creeping and prostrate-ascending habit. The stems are thin, branched, glabrous or with patent or reflexed hairs, rooting at the nodes in contact with the soil, but lacking underground stolons. The root is taproot, gradually tapered and sometimes woody at the base.

The leaves are alternate, trifoliate, with a petiole length from 1 to over 8 cm, and have small rectangular, auriculate stipules adherent to the petiole. The leaflets are obcordate in shape, with a bilobed apex, about 5–9 mm long by 8–12 mm wide, of herbaceous texture. The color can vary from green to green spotted with violet, with variable pubescence on both surfaces, more often on the underside.

The flowers are hermaphroditic, small to medium-sized (5–7 mm petal length), bright yellow in color, often with reddish streaks at the base and on the outer face of the petals. They are gathered in umbelliform inflorescences of 2–7 flowers, located in the axil of the cauline leaves. The calyx consists of 5 lanceolate-linear sepals, about 4 mm long, with ciliate margins especially at the apex. The floral peduncle is pubescent, similar or shorter in length than the leaf petiole, and bends after flowering. The stamens are 10, with the 5 inner ones longer and opposite the petals. The ovary is superior, with 5 carpels and as many styles with capitate stigmas.

The fruit is a fissuricidal capsule, cylindrical, with a star-shaped pentagonal cross-section, 8 to 25 mm long and 2–3 mm wide, covered with simple hairs (hirsute) and with few setose hairs along the dehiscence fissures. Each locule contains 3 to 8 ovoid, compressed seeds, about 1 mm, brown-reddish, with 6–8 transverse ridges and lacking white lines.

Habitat and distribution

Cosmopolitan species widely distributed throughout the Italian territory and the Mediterranean basin, it is particularly common in anthropized environments. It grows spontaneously in cultivated fields, gardens, threshing floors, sidewalks, wall cracks, and disturbed areas. It prefers well-drained soils, often sandy or gravelly, with sunny or partially shaded exposure.

In Italy it is found from the plain up to about 800 meters altitude, more frequently present in hilly and flat areas. In the Mediterranean the species is common in central and southern regions, less frequent in higher mountainous areas and colder northern regions.

Flowering period

Flowering extends from April to October, with some geographic variation linked to the local climate: earlier and prolonged in mild and Mediterranean climate areas, more concentrated in the summer months in cooler or mountainous zones.

Ecology and pollination

The plant is mainly pollinated by pollinating insects attracted by the bright yellow color of the flowers. The umbelliform inflorescence facilitates access to pollinator visitors, which include small hymenopterans and other phytophagous insects. The reproductive strategy is predominantly entomogamous, with hermaphroditism and prolonged flowering.

Seed dispersal occurs through the fissuricidal capsule which, opening, releases the seeds that fall on the surrounding soil; the presence of hairs on the capsule and on the fruit surface may facilitate limited mechanical or animal transport. The stems rooting at the nodes allow the plant to expand vegetatively, favoring colonization of disturbed habitats.

Curiosities and traditional uses

The genus name Oxalis derives from the Greek “oxys” (acid) and “hall” (salt), referring to the high content of oxalic acid present in the leaves and flowers, giving them a characteristic sour taste. The specific epithet “corniculata” means “horned”, probably referring to the elongated shape of the fruits.

In ethnobotany, field wood sorrel has traditionally been used for its medicinal properties: anti-inflammatory, astringent, depurative, diuretic, febrifuge, and stomachic. The leaves and flowers, rich in vitamin C, have been used for treating fever, influenza, diarrhea, traumatic lesions, and urinary tract infections, as well as against scurvy.

Externally, leaf extracts are used to soothe skin eruptions, insect bites, and burns. In cooking, the leaves can be eaten raw in salads or the flowers used as decoration, but always in moderation due to the oxalate content which can be toxic for people with kidney or joint problems.

From a dyeing perspective, the plant is known for producing yellow, orange, and red colors.

Etymology

The scientific name derives from Greek: “Oxalis” from “oxys” (acid) for the sour taste due to the oxalic acid contained in the plant, while “corniculata” (from Latin) means “provided with small horns”, probably referring to the shape of the elongated and pointed fruits. The common Italian name “acetosella dei campi” also recalls the sour taste (“vinegar”) and the frequent habitat in open fields.

Sources

• Prof. S. Pignatti, Flora d'Italia
• Acta Plantarum – Flora delle regioni italiane (scheda di Marinella Zepigi)
• Tela Botanica / H. Coste, Flore descriptive et illustrée de la France
• World Flora Online (WFO)