Oxalis exilis aka Least Yellow Sorrel

Oxalis exilis belongs to the wood sorrel family, Oxalidaceae. Its common names include least yellow sorrel and shady woodsorrel. It comes from Australia, Norfolk Island and New Zealand. Kew places it within a subtropical climate range. Kew lists it as a perennial. Plants For A Future also records an annual life cycle. This small plant grows in gardens, crop fields and waste ground.

Plants reach about 0.33 feet (0.1 metres) in height. They spread to about 1 foot (0.3 metres) across. The leaves are small, which makes picking them slow work. They have a sharp, sour taste due to oxalic acid. Plants For A Future gives June to September for flowering. Each flower has both male and female parts. Insects pollinate the flowers, and plants can also fertilise themselves. The plant spreads through seeds and underground bulbils.

It grows with little effort in a warm, dry site. Plants For A Future says it needs a site without shade. Sandy soil suits it, but loam and clay also work. The soil should drain well, whether it stays dry or moist. It tolerates mildly acid, neutral and mildly alkaline soil. The source lists USDA zones 4–8 and reports frost tolerance. Its separate UK zone 5 label uses a different scale. That label does not establish an RHS hardiness rating.

Its small size allows it to grow in cultivated beds. Yet its spread can make it an unwelcome garden weed. Seeds and bulbils let it spread fast once established. Plants For A Future describes it as troublesome in nursery pots. It can also cause problems among greenhouse plants. That detailed account conflicts with the source's brief negative weed flag. The account gives stronger grounds for caution about its spread. Its ability to grow with little help also limits propagation needs.

The leaves can be eaten raw or cooked, in small amounts. They add sour flavour to salads or mixed cooked greens. The flowers are also edible raw and taste tart. Leaves may remain available unless winter cold becomes severe. Their oxalate content makes large servings unsafe. Oxalic acid can reduce the calcium available to the body. Cooking lowers the amount of this acid in the leaves. People with kidney stones, gout or arthritis need extra caution. Plants For A Future also records traditional medicinal uses. These records do not establish that home treatments work or are safe.