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Erophila glabrescens Jord., Glabrous Whitlowgrass

Account Summary

Native, very rare, but almost certainly under-recorded. The world distribution range is uncertain.

23 April 1999; Northridge, R.H.; hard shoulder alongside the Enniskillen-Belfast road near Coollane.

April to May.

Very little work has been done on separating the various species and subspecies of the Erophila verna (Common Whitlowgrass) complex in the Fermanagh survey, a situation which so far is the case throughout most of the British Isles (New Atlas).

E. glabrescens first appeared in a national Flora as a separate taxonomic entity in the third edition of the Flora of the British Isles by Clapham et al. (1987), a source of information not consulted since it was quite rapidly and almost completely superseded by Stace's (1991) New Flora of the British Isles. During most of the Fermanagh flora survey RHN and the current author (RSF) preferred to carry around and rely on as our field identification yardstick, the sixth edition of An Irish Flora (1977). Knowing now what the available alternative was (Stace 1991), this is quite a major confession.

The significant paper on the British Isles distribution of the constituent taxa of the Erophila verna polyploid complex, based largely on herbarium records, (Rich & Lewis 1999, Table 1 and Fig 4) showed that, in Ireland, E. glabrescens had at that time a total of 39 records from 32 hectad grid squares. Fermanagh was not represented in the paper though a total of just three records did exist from N Ireland sites: one each from Cos Tyrone, Down and Antrim (H36, H38 & H39). Three years later, Preston et al. (2002) published a map with records from two additional N Ireland hectads, adding grid square J34 in Co Down and the first Fermanagh record given above, from grid square H33. There are now two additional Fermanagh records in the new century and they lie in contiguous grid squares, H15 and H24. The sites are on roadsides along the lowland axis of the county, in or near the only substantial conurbation, namely Enniskillen town. All three Fermanagh records were made by RHN and the remaining details of the other two are: on Sligo road, Enniskillen town, 4 May 2000; abundant in the car park at Tully Castle, Lower Lough Erne, 16 April 2001. The habitats involved are lowland, artificial and disturbed, ie roadside verges or hard shoulders, and a tarred public car park.

It is quite clear from this evidence and from the comment of D.A. Pearman and C.D. Preston in the brief species account accompanying the B & I hectad map in the New Atlas, that being a small and rather insignificant looking ephemeral spring annual and, furthermore, a polyploid taxon or species that habitually selfs, E. glabrescens is difficult to reliably distinguish from E. verna s.s. It therefore remains seriously under-recorded throughout the British Isles. This is especially so in Ireland in comparison with Britain, since a very much smaller population of sufficiently expert recorders is resident and active.

Growth form and preferred habitats

This is a small, rosette-forming, ephemeral, winter annual of dry, shallow, nutrient-poor, neutral to calcareous soils. In much of B & I, Erophila verna s.l., or the polyploid species aggregate is generally common and predictable in any open, disturbed habitat having a high proportion of bare soil. It often occurs in a wide range of linear or urban situations including, in B & I, both coastal and inland examples, in base- or lime-rich, sandy, stony or rocky soils (Salisbury 1964; Preston et al. 2002).

Man-made habitats include paths, or in mortared crevices of pavements and walls, plus alongside railway tracks where these survive (Salisbury 1964; Sinker et al. 1985). E. verna is tolerant of exposure and is widespread at low to medium altitudes throughout B & I and more rarely up to around 2,400 ft (730 m). It is completely absent from Shetland and becomes increasingly rare or absent in the more acidic soils and the wetter conditions of W Ireland, NW Scotland and the English Midlands (Salisbury 1964; Preston et al. 2002).

Fermanagh occurrence

In Fermanagh, E. verna s.l. is occasional only, or infrequent, and has been recorded in 40 tetrads, 7.6% of the total in the VC. It is found in a wide range of artificial and semi-natural habitats from urban waste ground, along roadsides (and previously along railway lines), plus lakeshore, wayside gravel, car parks, paths, slipways and quarries. As the tetrad distribution map clearly shows, although decidedly uncommon, the distribution of E. verna s.l. very definitely follows linear habitats – both artificial (roads) and semi-natural (rivers). For a number of years, E. verna s.l. grew in long swathes on the gravel covered hard shoulder alongside the Enniskillen to Belfast road for some kms. In this site, the flowers in early spring were so dense they resembled a recently fallen shower of hailstones. Subsequent road works tarred over many of the areas where the plant previously grew so abundantly and to date it has not re-established in this site to anything like the same extent.

Flowering reproduction

The leafless stems produce a variable number of small white flowers with deeply notched petals from the beginning of March until June. Growing as they do in open, often exposed and disturbed, shallow infertile soils, plants of E. verna are typically very small or dwarfed, and they tend to produce only a few fruits per plant. In Norfolk sand dunes, for example, Kelly (1984) found that plants were seldom more than 4 cm tal and a many were less than 1 cm tall. Small plants produce very few fruits and Kelly's work proved that so-called 'depauperate' plants bearing only one or two fruits also produce reduced mean numbers of seeds per fruit. The mean number of fruits on the Norfolk dune E. verna plants varied over three years between 1.54-2.39 per plant, yet despite such low figures the plant populations of E. verna and five other associated 'depauperate' species, appeared relatively stable in numbers.

E. verna flowers habitually inbreed, self-pollination automatically occurring when the outer stamens dehisce immediately adjacent to the ripe entire stigma (Rich 1991).

Seed dispersal, survival and ecology

The winter annual life cycle, which is so frequently and so well displayed in small, short-lived cruciferous species like E. verna, may be considered a very effective drought-avoiding syndrome. The small seeds of these little annuals facilitates wind dispersal of the species and, in this particular case, the seed also displays remarkable longevity, surviving five or more years in the soil seed bank (Thompson et al. 1997). Germination drops off very rapidly after the second year of storage in damp soil, however. In a Polish sand dune experiment, an average of only 5.7% of the E. verna seeds present in the surface layers germinated in the spring under natural conditions, although recruitment (referred to as 'natality', which really means 'birth rate' (Holmes 1979)) varied greatly (as expected) with existing plant density (Symonides 1984).

The early spring flowering of E. verna has traditionally been used by farmers in some parts of the British Isles as a guide to when conditions are suitable for sowing spring barley (Vickery 1995).

Variation

Erophila verna s.l. is a species aggregate or complex which consists of a large number of morphologically different cytotypes, each exhibiting genetic constancy. The 19th century French botanist Alexis Jordan set out to distinguish and describe these local populations and as a result of his collections and their subsequent cultivation, he was able to describe 53 "elementary species" and recognise more than 200 distinct genetic "lines" or "morphs" in the genus (Briggs & Walters 1997, pp. 30-1). The situation is maintained by habitual, long-term inbreeding. This in turn has created homozygous, true-breeding, pure genetic lines that are morphologically distinct, eg differing in fruit shape, size, seed number per fruit and pubescence (Proctor & Yeo 1973; van Andel et al. 1986). This situation led Filfilan & Elkington (1988, 1998) following the earlier study of Winge (1940), to delimit four forms within the species complex with differing chromosome counts between 2n=14 and 2n=64, recognising each of them at the species level. One of these cytotypes with 2n=24 (E. semiduplex Winge), appears confined to Germany, but the other three forms occur in B & I. So far, only one of these segregates has been recognised in Fermanagh (see E. glabrescens Jord. below) and their true distribution in B & I has yet to be properly determined (Rich 1991, pp. 256-9; Filifilan & Elkington, in: Rich & Jermy 1998, pp. 126-8; Preston et al. 2002).

While these new forms (species or otherwise) may prove useful constructs, Kelly's study should still be borne in mind. The fact remains that Symonides (1983, 1984) found that individuals of E. verna respond in a plastic manner to seedling population density. Also, van Andel et al. (1986) discovered a strong correlation between plant morphology and seed weight in populations of E. verna and this in turn reflects multi-niche selection and adaptation to environmental 'uncertainty'. This may reflect, for example, soil moisture and nutrient levels and, possibly, also the effect of plant burial by blown sand in dune populations.

The existence of highly inbred annuals appears to contradict both the Darwinian principle that Nature abhors perpetual self-fertilization and the Mendelian notion that crossing, even if only occasional, is essential in order to maintain genetic fitness. As with every situation in life, in reproduction there are costs and benefits to be analysed and the balance of outcomes closely depends on the particular circumstances, rather than a simple 'one size fits all' scenario. Forms of E. verna with relatively large seed, for example, may enjoy a competitive advantage allowing rapid early growth of seedlings and might result in these plants overtopping surrounding vegetation. Other morphs with a smaller seed size may allow the fruiting plant to produce greater numbers for the same outlay of resources, thus conferring significantly greater powers of dispersal into bare ground, or enabling colonisation of sites where seedlings face less competition, or occupy a more mesic, less ecologically testing environment.

Habitual selfing is particularly common in polyploid plants such as E. verna s.l. and its close relatives, in which the chromosome number has increased (usually doubled), often following hybridisation. It has been suggested that the extra genetic material that this process creates, may well reduce or dilute the effect of deleterious mutant genes that inevitably accumulate over time in this type of ± continually selfing species (Proctor et al. 1996, p. 335).

European and world occurrence

Erophila verna s.l. or the species aggregate is considered native in large parts of Europe, N. Africa and W Asia (Hultén & Fries 1986, Map 966), but the complicated taxonomy and recent subdivisions has led to a great level of uncertainty as to the distribution of species (or subspecies) and varieties, so they really are unknown at present.

Names

The genus name 'Erophila' comes from the Greek 'er' meaning 'spring', and 'philos' meaning 'loving' (Stearn 1992). The Latin specific epithet 'verna' means 'of the spring' and is very appropriate. The English common name 'Whitlow Grass' was first coined by Gerard (1597) for this medicinal plant, which was too inconspicuous to have acquired common names (Grigson 1974). The species was known to 16th century herbalists as 'Paronychia vulgaris', from its use in (supposedly) curing a whitlow (in Latin, paronychia), ie any pussy inflammation at the nail of a finger or toe (Watts 2000). The word 'whitlow' is a 14th century modification of the previous 'whitflaw', thought to be derived from 'white flaw' (Hanks 1986).

Threats

None.