Sorrel is a native creeping herbaceous plant in Hong Kong, commonly found in urban parks and along roadsides. Its leaves are composed of three obcordate leaflets, which fold like an umbrella at night or during rainy weather.

Although Sorrel and its congener Lavender Sorrel (Oxalis debilis subsp. corymbosa) are similar in shape, their flower colours and reproductive methods are distinctly different: the flowers of Sorrel are yellow in colour, and when its okra-like capsules ripen or are subjected to external force, the pods burst open instantaneously like “popcorn,” flinging the seeds out for a distance; whereas the flowers of Lavender Sorrel are pink-purple in colour, and the plant rarely bears fruit, as it reproduces asexually through underground bulbs most of the time.

Both Sorrel and Lavender Sorrel contain oxalic acid and are locally known as “Sour Grass” (酸味草). The whole plant of both species can be used medicinally. In addition, Sorrel is the larval food plant of the butterfly Pale Grass Blue.