Lysimachia arvensis), commonly known as the scarlet pimpernel, red pimpernel, red chickweed, poor man's barometer, poor man's weather-glass,[1] shepherd's weather glass or shepherd's clock, is a species of low-growing annual plant with brightly coloured flowers,[2] most often scarlet but also bright blue and sometimes pink.

[4] A. arvensis is now naturalised almost worldwide, with a range that encompasses the Americas, Central and East Asia, the Indian Subcontinent, Malesia, the Pacific Islands, Australasia and Southern Africa.

The orange, red or blue, radially symmetric flowers, about 10–15 millimetres (0.4–0.6 in) in diameter, are produced singly in the leaf axils from spring to autumn.

The stamens have lollipop hairs and therefore attract a variety of pollinators, especially flies, but the flowers are also capable of autopollination.

The petals of the type arvensis are bright red to minium-coloured; carnea is deep peach, lilacina is lilac; pallida is white; and azurea is blue.

Anagallis arvensis is generally unwelcome as a cosmopolitan invasive species; it is harmfully toxic in several respects and accordingly undesirable in pastures.

Anagallis has been used in treatment of non-specified types of phthisis, and of kidney-related conditions such as dropsy and chronic nephritis.

Taken by mouth, experimental doses of the liquid in humans caused twenty-four hours of intense nausea, headache and bodily pain.

Reports from Australia state that when grain crops have been infested by the weed, chaff that contains much of the material becomes unpalatable to stock as fodder.

[15] Reportedly an Indian practice of expelling leeches from dog nostrils can lead to fatal results if the animal swallows the fluid.

[20] The Scarlet Pimpernel is the alias of Sir Percy Blakeney in the novel of the same name by Baroness Emma Orczy and its numerous film and musical adaptations.