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Valerianella locusta (L.) Laterr., Common Cornsalad

Account Summary

Native, very rare, possibly only casual. European temperate.

1934; Praeger, R.Ll.; Enniskillen Town.

May and June.

Growth form and preferred habitats

A small, rather brittle, repeatedly branched into two divisions (ie forking), nearly hairless, annual with spoon-shaped lower leaves and oblong upper ones (Hutchinson 1972). V. locusta is a winter-annual of dry, sandy to calcareous soils in open or disturbed habitats. It undoubtedly was more frequent in the past as a cornfield weed before the intensification of agricultural production, improved scientific seed cleaning and the extensive use of herbicides reduced its prevalence in the post-war period from 1945 onwards. It germinates in the autumn and overwinters as a green rosette of crowded pairs of strap-shaped leaves. The plant is delicate, branching, 10-20(-30) cm tall, with opposite, sessile, entire, or slightly and shallowly (weakly) toothed leaves.

V. locusta can occur on moist to dry, acid to calcareous soils, but does not tolerate shade or competition from taller or more vigorous species, but rather is favoured by occasional disturbance (Sinker et al. 1985; Fitter 1987). With the marked decline of V. locusta in arable agricultural fields in B & I, V. locusta is now more frequently recorded on dry, rock outcrops, stony places, screes and in coastal sand dunes and shingle, but it also features in a wide range of disturbed dry ground situations, including on wall-tops or at their base, in paving cracks, gravel paths, in gardens, graveyards, quarries, roadside verges, bare places in grassland, dry banks and in railway and dockyard settings (Sinker et al. 1985; P.J. Wilson, in: Preston et al. 2002). The established strategy of V. locusta is categorised as SR, meaning it is a Stress-tolerant Ruderal species (Grime et al. 1988, 2007).

Flowering reproduction

In spring and summer, from April to August, V. locusta produces clusters of tiny, bluish flowers in dense cymose heads surrounded by small, leafy bracts. The flowers have very small, regular, funnel-shaped, 5-lobed, pale lilac corollas. The three stamens and the 3-lobed stigma mature at the same time and the flowers automatically self-pollinate if insects fail to cross-pollinate them (Hutchinson 1972).

In fruit, the calyx is absent or vestigial, persisting as a single very small tooth on top of the inferior ovary which is now a single-seeded nutlet with two empty loculi attached to it. (Flora Europaea 4, p. 50 notes, the "calyx reduced to a minute tooth above each loculus", ie three minute teeth should therefore be present on the top of the fruit.)

The three loculi are only really visible in cross-section and a ripe fruit, good eyesight, a sharp knife, a top of the range pair of forceps, good handling skills with tiny structures and a strong hand-lens or a dissection microscope are minimum requirements for confident determination (Salisbury 1964; Hutchinson 1972; Fitter 1987; Perring & Walters 1989; Crawley 2005; Sell & Murrell 2006; Parnell & Curtis 2012). A cross-section of the fruit shows a single plump fertile locule (or cell), overshadowing the two neighbouring sterile, empty locules, which can be very reduced in cross-section (Parnell & Foley 2000). Excellent drawn illustrations comparing the fruits of the different species both before and after sectioning are contained in Webb et al. (1996) and Parnell & Curtis (2012), while Stace (1997, 2019) display good quality, helpful, comparative photographs of whole fruits of Valerianella species.

The minute nutlet is ribbed, the chamber containing the seed having a corky back. The actual seed is flattened on one side (Melderis & Bangerter 1955).

After fruiting and seeding the plant withers and quickly disappears.

Identification

Valerianella species can be somewhat difficult or uncertain to recognise without ripe fruits. In V. locusta, the fruit is described as 'chestnut shaped', about twice as long as wide in side view, with a shallow groove on the abaxial face separating the two sterile cells (loculi) from the solitary, third fertile one (P.J. Wilson, in: Rich & Jermy 1998; Crawley 2005; Parnell & Curtis 2012). The species most similar and likely to be confused with V. locusta is V. carinata (Keeled-fruited Cornsalad), since they occur in similar or the same range of habitats. V. carinata is more exclusively found in man-made habitats and is possibly being spread accidentally by man at the present time. The fruit of V. carinata is ± quadrangular in side view (P.J. Wilson, in: Rich & Jermy 1998).

British and Irish occurrence

In Britain, V. locusta is a rather local species, much more prevalent in the south than elsewhere, and it becomes almost entirely coastal north of Cumbria. In Ireland, by comparison, it is thinly scattered and displays a somewhat more easterly occurrence (New Atlas). In the NE of Ireland, this little plant is decidedly coastal and it is very much rarer inland (Flora of Lough Neagh; FNEI 3).

Coastal plants of V. locusta tend to be dwarf and most probably belong to var. dunensis, which is more compact and cushion-like in habit, with leaves up to only 3.5 cm long, compared with up to 7 cm long in V. locusta var. locusta (P.J. Wilson, in: Rich & Jermy 1998).

Fermanagh occurrence

In Fermanagh, V. locusta is a very rare, possibly only a casual species of disturbed ground and walls near habitation. There are records in just five tetrads; four of them with post-1975 dates were found by RHN. The remaining details are: dry bank, lakeshore and pathway, Goblusk Bay, Lower Lough Erne, 17 July 1988; refound here June 2003 and July 2010; Clabby Village, 4 June 1991; Old Crom Castle, Upper Lough Erne, 21 May 1999; still there 2007; Drumelly Rocks, 4 km NW of Belcoo, 4 April 2009, RHN & HJN.

The Clabby Village record was from a gravelly area and the species did not persist there. At the old ruined castle at Crom, near the lough shore, it grows on and at the base of the walls, where it is thought to possibly have persisted for many years, as is certainly the case at Goblusk Bay.

European and world occurrence

In phytogeograpical terms, V. locusta belongs to the European temperate element and occurs in W, C & SE Europe, but it is rare in the north, including all of Scandinavia. It is also present in Madeira, N Africa and W Asia. Since it was cultivated as a kitchen garden plant, it has been introduced into both east and west of N America, S America and New Zealand (Hultén & Fries 1986, Map 1739).

Names and uses

The genus name 'Valerianella' is the diminutive of 'Valeriana', which is a medieval name, perhaps derived from 'valeo', meaning 'be well' or 'health'(Gilbert-Carter 1964; Gledhill 1985). The Latin specific epithet 'locusta' means 'spikelet' in botanical Latin and it is applied to V. locusta from the form of the partial inflorescences (Gilbert-Carter 1964).

As the common names 'Cornsalad' and 'Lamb's-lettuce' suggest, this little annual is edible and, indeed, the crowded leaf rosettes in the winter condition were popular in earlier, hungrier times as an early spring salad vegetable (Salisbury 1964; Allan 1978). Grieve (1931), who describes the garden cultivation of it, quotes Gerard's Herball (probably Thomas Johnson's 1636 edition), "We know Lamb's Lettuce as Loblollie; and it serves in winter as a salad herb among others none of the worst.". The small-leaved rosettes are described by Mabey (1996) as having a succulent texture, but little flavour, and while larger-leaved varieties have been selected and developed more recently, he considers they have even less culinary merit than the wild form.

Threats

None.

References

Hackney, P.( Ed.) and Beesley, S., Harron, J. and Lambert, D. (1992); Harron, J. (1986); Salisbury, Sir E. (1964); Allan, M. (1978); Mabey, R. (1996); Grieve, M. (1931); Grime et al. 1988, 2007; Hultén & Fries 1986; Rich & Jermy 1998; Hutchinson 1972; Fitter 1987; Perring & Walters 1989; Crawley 2005; Sell & Murrell 2006; Sinker et al. 1985; Gilbert-Carter 1964; Gledhill 1985; Melderis & Bangerter 1955; Parnell & Curtis 2012; Parnell & Foley 2000; Tutin et al. 1976. Preston et al (2002); Webb et al (1996); Stace (1997, 2019); Gerard Herball