The WALA Plant Library
Wood Sorrel

Synonyms for Wood Sorrel: Common Wood Sorrel, White Wood Sorrel, Cuckoo Bread, Cuckoo's Meat, Shamrock
Scientific Name: Oxalis acetosella L.
Family: Oxalidaceae (Wood-Sorrel family)

Description:

A walk in the woods, especially in spring in shady areas, can bring a welcome glimpse of vivid, fresh green – Wood Sorrel, which can reach a height of 15 centimetres. Despite its delicate nature, it has a powerful radiance which from April to June is emphasised by its white, red-veined, five-petalled flowers. A cell turgor pressure mechanism causes the heart-shaped, trifoliate leaves to fold up under some conditions. These include vibration, too much warmth or light, or the influence of the circadian rhythm. It is marvellous to see how the Wood Sorrel lets its leaves swing like pendulums in the morning, as if to greet the new day. As night approaches the leaves fold in upon themselves. The flowers, too, close at twilight and bow their heads as if the plant were settling down to sleep.
Wood Sorrel only feels at home in moist, semi-shady areas. No other native flowering plant thrives on so little light as this one. It achieves its full quota of photosynthesis with just ten percent of the daylight. It can even survive on just one percent daylight. In shady areas it carpets the ground by allowing its stems to branch and grow horizontally under the surface. The axillary buds occurring at intervals along these stems produce new tufts of leaves and side shoots in a kind of snowball system.
When its seeds are ripe, Wood Sorrel becomes a kind of firing range. Pressure in the seed capsules builds until it reaches as much as 17 bar. This pressure is enough to catapult the mature seed some 2.5 metres away from the mother plant. Sometimes a seed will land on a tree, where Wood Sorrel also feels quite at home and thrives. If it lands on moist soil, tissue in the seed swells, causing it to burst and propelling the seed once more through the air for as much as a metre.
Incidentally, Wood Sorrel not only grows the bright white flowers which open up to allow pollination by insects and bees. In summer and autumn, pinhead-sized flowers develop which remain closed and pollinate themselves. It is not known why the plant produces these flowers, which are known to botanists as cleistogamous, or hidden, flowers.