Scarlet pimpernel

Image by: James Altland, USDA-ARS
Foliage of scarlet pimpernel is opposite and can reach 1 inch in length. Leaves sometimes may occur in whorls of three.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Scarlet pimpernel has relatively thick leaves with the midrib visible as a depression in the leaf blade.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Stems of scarlet pimpernel are noticeably angular. This feature alone can be used to distinguish it from chickweeds.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
The orange to salmon color of the scarlet pimpernel is a unique indentifying feature of this weed.
Image by: James Altland, USDA-ARS
Anagallis arvensis
Family: 
Primulaceae
Life cycle: 
Annual
Habit: 
Scarlet pimpernel has a prostrate and spreading habit. In open nursery fields, this weed will form a circular mat up to 2 feet wide. Scarlet pimpernel foliage is small, acuminate (sharp pointed tip), sessile (without petioles) and glabrous (without hairs). Foliage is oppositely arranged along the stem, with each leaf pair growing on a plane perpendicular to the previous and next pair.
Flowers: 
Scarlet pimpernel flowers are solitary, small (about 1/4 inch diameter), and somewhat showy. Flowers are orange to salmon in color with 5 petals and 5 stamens. The center of the flower often appears blue to purple in color.
Favorable environments: 
Field
Favorable environment notes: 
Scarlet pimpernel grows in a variety of field environments such as agricultural crop fields, vineyards, orchards, pastures, grasslands, landscaped urban areas and other disturbed sites such as roadsides.
Dissemination: 
Scarlet pimpernel reproduces by seed. Tiny round fruit capsules, often less than ΒΌ inch, produce three sided, black to brown football shaped seeds. These seeds are very tiny, ranging from 1.0-1.5 mm in size.
Of interest: 
Scarlet pimpernel is also sometimes called poison chickweed. It contains notable toxins, particularly saponins and cytotoxic cucurbitacins. If consumed, it can be toxic to livestock and humans. It is often confused with the edible common chickweed, Stellaria media. Another common name, 'Poor man's weather glass', is in reference to its small orange flowers that close up quickly as bad weather approaches.