This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
This plant is found in older Glacial, Neolithic, and Roman deposits. It is confined to the Cold North Temperate and Arctic Zones in Arctic Europe and Siberia. The Ragged Robin is found in every county in Great Britain, and in the Highlands at a height of 2000 ft.
Almost every meadow, field, and pasture, especially those which border marshy tracts or wet spongy ground on the sides of hills, is made gay with the feathery pink petals of the Ragged Robin in spring. It is especially fond of growing in the spongy, wet ground, surrounding a pond where Marsh Orchis, Toad Rush, Horsetails, Valerian, and other paludal species or marsh plants congregate.
The tall, slender, erect, nearly angular, furrowed stems are ascending, and have swollen joints, and are covered with hairs bent downwards, being purple in colour. Ragged Robin has the radical leaves blunt at the tip, with stalks, and narrow stem-leaves. The lower part is clothed with bristles, the upper is clammy.
The flowers are pink, and the petals divided into four parts, with an appendage on the upper side at the base of the limb. The narrow segments are erect and have a tooth on the outer margin. The flowers are in a loose cluster. The calyx is purple and has ten ribs. It is tubular and expanded. On the petals the hair is as long as that on the calyx. The capsule has five teeth bent inwards. There are no divisions in the fruit, and the seeds when the capsule opens are exposed to the wind.
Ragged Robin is often 3 ft. high. This pretty plant may be found in flower in May and June. It is perennial and increases by division.
The honey is placed in a position in the flower which is intermediate compared with the place of the honey-glands in Stellaria, Cerastium, and Gypsophila, where the honey is easily accessible, and in Dianthus and Saponaria, where it can only be reached by long-tongued Lepidoptera.
The nectaries unite in a fleshy ring round the ovary at the base of the stamens. The calyx is only 6-7 mm. long, with teeth 3 mm., which are erect, and support the claws or stalks of the petals. Insects with a proboscis 9 - 10 mm. long can thus reach the honey, and those with a proboscis can push the calyx-teeth to one side, whilst some insects are small enough to creep down the tube. The anthers ripen first. The five outer anthers open first and occupy the entrance to the flower, their pollen-covered sides are turned towards each other, and pollen is conveyed to the proboscis owing to the crowded corolla-mouth. The stamens next elongate and bend, so that they lie in the space between the petals, and the inner whorls occupy the middle. When they wither the five styles arise under the stigmatic papillae. The styles move as far as the entrance, making 1 1/2 or 2 spiral twists.