Erophila verna (Common Whitlowgrass)

Plant of the week
Picture of Erophila verna (Common Whitlowgrass)
Erophila verna (Common Whitlowgrass)

This week’s #SxPOTW is another from the cabbage family (Brassicaceae), and our smallest so far. It is also the first #SxPOTW ‘by popular request’. I say popular: one person emailed our webmaster to suggest it. And why not? It is a lovely plant. Very inconspicuous, yet delicate and charming on close acquaintance. You can see from the close-up of the flower how tiny it is. That it is a crucifer (another name for plants in the family) is nevertheless clear: four petals alternating with the four sepals; six stamens; fruit a capsule opening with two valves from the bottom.

Picture of Erophila verna (Common Whitlowgrass)
Erophila verna (Common Whitlowgrass)
Picture of Erophila verna (Common Whitlowgrass)
Basal rosette of Erophila verna (Common Whitlowgrass)

In this case the petals are deeply bifid (divided at least half-way to the base, usually more than half-way) and there are no leaves on the flower stem. The basal rosette of leaves is hairy and the hairs are forked (‘Y’-shaped), which you can just about make out in the photo. It tends to grow in open, dry habitats, especially calcareous rocks, walls, dunes and the edges of paths (as in this case). It is an annual and often grows in small colonies of varying sized plants. Some have a single unbranched flower stem whereas others have multiple, multiply branched inflorescences.

Picture of Erophila verna (Common Whitlowgrass)
Habitat of Erophila verna (Common Whitlowgrass)

As the entry in our magnificent Flora of Sussex (2018) attests, there are actually a number of closely related species and varieties. E. verna itself can be either var. verna or var. praecox. The difference is the shape of the capsule  – the latter being shorter and more rounded (length:width ratio <1.5) while the commoner former has longer ones. Whether var. praecox comes into flower earlier, as the name suggests, is not clear from the books. The fruits dry out to look like tiny fruits of Honesty (Lunaria annua). The specimen shown has capsules 0.3mm x 0.4mm to 0.5mm, making it var. praecox. (See here for picture of var. Verna capsules.)

Picture of Erophila verna (Common Whitlowgrass)
Fruits of Erophila verna (Common Whitlowgrass)
Distribution map of Erophila verna (Common Whitlowgrass) in Sussex
Distribution of Erophila verna (Common Whitlowgrass) in Sussex

Native. Sx: frequent, locally common. Dry open habitats. Occurs in a wide range of habitats ranging from walls and pavements to shingle and open ground on sand, chalk and gravel. The map clearly shows its preference for light soils. It requires the driest conditions and sometimes occurs on anthills on chalk downland. However it is seldom now seen there in the abundance implied by the Sx botanist Henry Salt in his book The Call of the Wildflower (1922): ‘One of the earliest and most welcome [of downland flowers] is the spring whitlow-grass, which abounds on ant-hills high up on the ridges, forming a dense growth like soft down on the earth’s cheek.’ There are several large populations on new pavements and roundabouts, where it may be on introduced construction material. Var. praecox has been identified occasionally. The map may include a few records of E. glabrescens and E. majuscula.

Source: E. verna (L.) DC. Common Whitlowgrass, The Flora of Sussex (2018)

The other two species are E. glabrescens and E. majuscula, Glabrous and Hairy Whitlowgrass respectively. They both have less deeply notched petals (maximum halfway, but often less). The former does have a few hairs around the edges of the leaves and on the lower part of the stem, but the leaf blade (lamina) is often noticeably shiny. The petiole (leaf stalk) is also often noticeably longer than the lamina. The latter is the rarest of the group, with a dense covering of grey-green hairs around the base, extending up the stem to the peduncles (flower-stalks). It also has much smaller seeds (0.3mm-0.5mm).

Distribution map of Erophila glabrescens (Glabrous Whitlowgrass) in Sussex
Distribution of Erophila glabrescens (Glabrous Whitlowgrass) in Sussex

Nearly all our records are of E. verna  in the wider sense (often recorded as E. verna agg. for ‘aggregate’) with the varieties rarely recorded. So this presents an easy opportunity for people to send in detailed records and make a name for themselves.

The common name relates to the species being used by herbalists in the past to treat whitlows, which are infections of the fingers caused by herpes simplex viruses. A number of species carry the name, including those from the genus Draba, which differ from Erophila in having stem as well as rosette leaves. Only D. muralis is known in Sussex from one site and is thought to be an introduction.