This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
No trace of this plant has occurred in ancient deposits. It is found south of Belgium throughout Western Europe. The Yellow Fumitory is found throughout England, Wales, and Scotland, where it is naturalized, and without exception an escape from cultivation. Almost entirely an escape from gardens it is likely to be found wherever it is grown in or near gardens. Its actual distribution as a naturalized plant has not been ascertained.
This plant has a predilection for walls, and is usually grown with other rock or mural plants in a garden or on the stone walls of a glass-house, or at the foot of the wall of a house. But it flourishes best, like the Ivy-leaved Toadflax, with which it grows, in old moated enclosures, where the bricks have fallen into decay, and a suitable substratum has thus been created for it. This is also the case with the Wallflower, Stock, and other mural denizens.
Unlike the Earth Smoke, Yellow Fumitory is a compact, many-branched, spreading plant, whose stems are less tall, and clustered together in a fastigiate manner, giving the plant, with its luxuriant foliage and rather abundant flowers, an ornamental character lacking in the latter.
The yellow, rarely white, flowers are in racemes, with a leaf opposite each, and the seeds are in 2-valved pods and numerous, while the bracts are small, oblong, shorter than the flower-stalks, and the seeds, which are granular, have a crest. The upper of the 4 petals has a short, thick, incurved spur. The foliage is more like that of an Adiantum, with inversely egg-shaped leaflets on long petioles. The whole plant is less bluish-green than Earth Smoke, but equally tender and brittle. The base of the stem and roots is yellow.
The stem is not more than 1 ft. high. Flowers extend from May to August. The plant is a deciduous, herbaceous perennial, increased by division.
When the hood is bent clown it does not rise again, but the stamens and pistil fly upwards, becoming concealed in the hollow of the upper petal, and the flower can only be visited once. The under side of the bee is dusted with pollen, heaped upon the stigma. Pollen is brought to the stigma if the bee comes from another flower. Bombus agrorum, with proboscis 12-15 mm., is the main visitor.
In Corydalis cava the flowers are larger and more conspicuous than in Fumaria, and have no power to self-pollinate, being sterile with their own pollen, and not perfectly fertile with pollen from another flower, but only so with pollen from a different plant. The tube is 12 mm. long, and hive-bees with proboscis 6 mm. cannot get at the honey, but only the humble-bee with proboscis 7-10 mm., though even they cannot easily get at it. The insect bites a hole at the base of the tube to reach the honey, and the visitors are Andrena, Sphecodes, Nomada, and Hive-bees (pollen-seekers).
Photo. Flatters & Garnett - Yellow Wall Fumitory (Corydalis lutea, D.C.)
The plant is dispersed by its own agency. The capsule is oblong, 2-valved, and swollen, and disperses the seeds, which are small, around the plant.
The name Corydalis given by Galen is the Greek Corydalis for Fumitory, and lutea is Latin for yellow, in allusion to the colour of the flowers. The English names are Lady's Pincushion, Mother of Thousands, Pincushion.