Oxalis corniculata Seeds | Creeping Wood Sorrel
LATIN NAME: Oxalis corniculata
COMMON NAME: Creeping Wood Sorrel
Plant Profile
Come back to a patch of this plant after dark and it has folded up. The three leaflets drop along their midribs and hang like a closed umbrella, then open again in the morning, and the whole colony does it in step. The movement is driven by a pulvinus, a swollen hinge of cells at the base of each leaflet and each leaf, where shifting ions change the water pressure on one side or the other. Nothing is wrong with the plant. It is settling down for the night.
The leaf is a clover-like trifoliate blade, with each leaflet heart-shaped and notched at the tip, and the whole thing is barely wider than a thumbnail. What separates it from a clover is the habit: the stems creep along the ground, branch freely, and root at the nodes wherever they touch moist soil, so a single seedling becomes a mat within a season. Cut the stems and the rooted sections carry on as independent plants.
The flowers are small, bright yellow and five-petalled, held singly or in twos and threes on slender stalks that stand clear of the leaves. They need almost no help: the plant sets abundant seed from its own pollen, and plants growing in dull or crowded ground often produce closed, self-fertilising flowers that never open at all. Seed production continues through the warm season, and a well-grown patch can put hundreds of capsules into the seed bank before the first frost.
The other yellow wood sorrel of the same ground holds itself up. The upright species has a distinct, sometimes branching stem that rises well clear of the soil, larger leaves and flowers, and it does not root at the nodes as freely. The creeping species stays pressed to the ground, has the stipules joined to the stalk, and roots as it travels. Both fold their leaflets at night and both taste of lemon, so the habit is the reliable difference.
Science & Biotechnology
The sour bite of the plant is oxalate. The leaves accumulate oxalic acid and soluble oxalates, which is why a single leaflet tastes like a squeeze of lemon, and why a sheep that grazes a heavy stand can be poisoned by the same chemistry. In the kitchen the taste is the point, and its concentration is enough that anyone with a history of kidney stones should leave the plant alone. The compounds are not destroyed by brief cooking, though boiling and discarding the water reduces them.
Uses & Benefits
The dark-leaved variant turns up in garden centres as a foliage plant for a pot or a gravel trough, where its bronze-purple carpet is genuinely handsome against pale gravel. The catch is that the plant you buy brings the same habit into the garden as the green weed: it creeps, it roots, it fires seed, and it will work its way into every neighbouring pot. Kept in a container on a hard surface and dead-headed before the capsules brown, it stays where it is put.
Where the plant is abundant and clean, the leaves are used as a sour green: chopped into a chutney with chilli and salt, scattered over a salad, or chewed in the field as a thirst-quencher by walkers and children who know it. In parts of Asia the whole plant is gathered as a pot herb and cooked with fish, and it appears in folk practice as a cooling wash for irritated skin. Pick only from ground you know has not been sprayed, and eat it in small quantities.
Growing from Seed
Control is a matter of timing rather than force. Hoe or hand-pull a patch while the flowers are open and the capsules still green, because a plant pulled after the capsules have yellowed will scatter its seed as it dries on the path. In greenhouses the plant travels on capillary matting and in the drainage holes of pots, so stand containers on a hard surface, weed the staging, and do not move soil from an infested bed into the cutting compost. Deep burying is a poor idea: the seed survives for years in the soil, and every digging brings a fresh generation to the surface.
If you are raising the ornamental form deliberately, treat the seed as small and light-hungry. Fill a pan with a light mix of two parts peat-free compost to one part coarse sand, firm it, and scatter the seed thinly on the surface, pressing it in with a board but covering it with no more than a dusting of sand. Stand the pan in a bright place out of full sun and keep the surface damp with a fine mist. The first true leaf is a single rounded blade and only later does the leaflet of three appear, so do not thin the pan until the trifoliate leaves are showing. Pot the seedlings on when they have three or four leaves each.
Our Take
This is a plant to admire in someone else’s gravel and to think twice about before introducing to your own. For sour greens that stay where they are planted, our notes on garden sorrel and sheep sorrel cover two leaf vegetables with the same lemony tang and a tidier habit, and purslane gives a fleshy, succulent alternative for a hot border. Pick early, pick clean, and never let a capsule go brown in the bed.
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