This small annual to perennial has quadrangular stems from the base that form a prostrate to upright habit. It has small bright green ovate leaves and the saucer-shaped scarlet flowers appear singularly from spring to summer. 

Hardiness zones 7 to 10

Anagallis arvensis is naturally found in western Europe growing in weedy places or vegetable gardens and in wasteland. It prefers a well drained, fertile to poor moist light soils that are high in nitrogen and grows in an open sunny position and is frost tolerant but drought tender.

The Scarlet Pimpernel is a fast growing bi-annual that is planted herb gardens for its herbal use or in pots and tubs. It is normally regarded as a weed that appears in potted plants or in disturbed soil. ID 824

Note:
Care should be taken as it self-sows readily and is controlled by removing young plants physically or apply glyphosate.  
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Anagallis (ăn-a-GAH-lis)  arvensis (ar-VEN-sis)

Primulaceae (PRIM-ew-LAY-see-ee)
Primroses