- Name also: Red Pimpernel, Red Chickweed, Poorman’s Barometer, Shepherd’s Weather Glass, Shepherd’s Clock
- Latin synonym: Anagallis arvensis
- Family: Primrose Family – Primulaceae
- Growing form: Annual herb.
- Height: 3–40 cm (1.2–15 in.). Stalk limp–erect, highly branched from base, 4-edged.
- Flower: Corolla regular (actinomorphic), wheel-shaped, brick-red or sometimes blue, 8–14 mm (0.3–0.6 in.) wide, fused, 5-lobed (deeply). Calyx lobed till base, lobes narrow with tapered tips. Stamens 5. Gynoecium fused, single-styled. Flowers usually in axillary pairs.
- Leaves: Opposite, stalkless. Blade ovate–elliptic, hairy underside, darkly spotted, with whitish, densely-haired, entire margin.
- Fruit: Spherical 5 mm (0.2 in.) long capsule with opening lid (circumscissile capsule).
- Habitat: Gardens, fields, roadsides, wasteland, loading places, ballast soil deposits. Casual alien.
- Flowering time: June–September.
- Harmfulness: Potentially or locally harmful alien species.
Scarlet pimpernel is a delicate annual member of the Primrose family that often grows along the ground. It is distributed across almost the whole of Europe. It is a poor competitor which favours places where the soil is almost free – it finds space in e.g. fields and gardens, and in the old days also in sailing boats’ ballast soil deposits.
Scarlet pimpernel’s scientific name, ‘adornment of the fields’, is very fitting, and it’s an interesting and rare plant. Its flowers close at midday, giving rise to one of its names in English: ’John-go-to-bed-at-noon’. They also close quickly when the sky clouds over or if rain is approaching, so it’s also known as Poorman’s Barometer. The species has red and blue-flowered forms, with the former being more common in Southern Europe and the latter being more common in the north. According to Central European herbalists the red-flowered form is especially good for men, while the blue-flowered plants are more suited to women. Research has shown however that the shoots contain toxic saponins and the roots cyclamens. People with sensitive skins can get reactions from merely touching the plant.