Draba verna

It is a small spring-flowering annual which is widely dispersed around the world, and which is found on walls, pavements and patches of bare ground.

The reason for this is that D. verna reproduces almost entirely by inbreeding (the flowers pollinating themselves immediately on opening), so a large number of genetically similar lines can be recognised.

These lines can even have different chromosome numbers (or ploidy levels), making them less compatible with other plants even when cross-pollination does occur.

The account here is for Draba verna L. in its original, aggregate, sense, although D. praecox and D. majuscula can be viewed as separate species.

[4][10] The common name "whitlowgrass" refers to an old meaning of the word, which Aulus Cornelius Celsus described as "a small piece of flesh [which] sometimes grows out from the nail, causing great pain; the Greeks call it pterygium.

[1][12] Common whitlowgrass is native to Europe, western Asia and parts of North Africa southwards to Ethiopia.

[21] Its Ellenberg values in Britain are L = 3, F = 3, R = 6, N = 3, and S = 0,[22] which shows that it favours relatively dry, neutral soils and low levels of fertility.

The other is a butterfly, the orange tip, which is a common species whose larvae feed on the flowers of plants in the cabbage family.

Two species of downy mildew infect common whitlowgrass, particularly when it is suffering from water stress: Hyaloperonospora erophilae coats the leaves and turns them chlorotic, whereas H. praecox has more localised and less obvious symptoms.

[24] In the 1600s Culpeper described it as "exceedingly good for those imposthumes in the joints, and under the nails, which they call Whitlows, Felons, Andicorns and Nail-wheals",[25] but Vickery[26] explains that it was never really used in folk medicine either in Britain or Ireland.

Flowers of common whitlowgrass
The leaves are often covered with forked hairs
The seedpods split open to leave just the translucent membrane that separates the valves.
Some leaves have a single tooth on one side of the leaf blade, resembling a whitlow.
Whitlowgrasses can look as if they have 8 petals
Whitlowgrass grows on bare soils, with the minimum of competition