Valerianella dentata (L.) Pollich, Narrow-fruited Cornsalad
Account Summary
Casual introduction, archaeophyte, locally extinct. European temperate.
1900; Tetley, W.N.; waste ground, Enniskillen town.
Growth form and identification problems
All Valerianella plants are small annual herbs with opposite and/or radical, undivided, oblong or spoon-shaped leaves. They have branched, repeatedly forked stems and tiny hermaphrodite or unisexual, slightly irregular, pale lilac flowers borne in terminal, bracteate, dense, cymose heads (Parnell & Foley 2000). The flower calyx is usually absent, or it can sometimes be represented by a small scale which persists and is attached to the top of the fruit formed from the inferior ovary after fertilisation. The minute flowers each have three stamens and the stigma is also divided into three branches. Each plant produces numerous 3-celled fruits, although the actual number is very variable (Parnell & Foley 2000).
V. dentata is very similar in general appearance to the much more common V. locusta (Common Cornsalad), but is more erect and is generally taller. V. dentata germinates in both spring and autumn, flowers during June and July and is self-pollinating. It survives best in less competitive spring-sown crops and also on arable field margins and in corners that escape intensive management (Garrard & Streeter 1983; A. Smith, in: Stewart et al. 1994). Its flower calyx, which surmounts the inferior ovary, has distinct, persistent teeth, one of which is much larger than the others. The fruit nutlet is sometimes smooth, but often is distinctly hairy, with two small ribs that incorporate the two other, very small, sterile cells or loculi of the ovary (Parnell & Curtis 2012).
The species of Valerianella are difficult to distinguish, ripe fruit generally being more or less essential for correct identification according to most Floras. The shape of the fruit is significant and the relative shape and size of the three loculi or cells inside it, ie comparison of the two sterile loculi and the solitary fertile one, is really only visible when a cross-section is cut and studied. Thus apart from needing a ripe fruit to examine, good eyesight, a sharp knife, top of the range forceps, a strong hand-lens or a dissection microscope and a fine degree of handling skills appropriate for very small objects are the minimum requirements for confident determination of Valerianella species (Webb et al. 1996; Stace 1997, 2019; Parnell & Foley 2000; Parnell & Curtis 2012). 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), and Stace (1997, 2019) displays good quality, helpful, comparative photographs of whole fruits.
Uniquely in V. dentata, the sterile loculi or cells are reduced to minute ribs; the fact that these 'ribs' represent ovary or fruit loculi or cells, is only clearly visible in cross-section. In the three other Valerianella species that occur in Ireland (V. locusta, V. carinata (Keeled-fruited Cornsalad) and V. rimosa (Broad-fruited Cornsalad)), the sterile cells are comparatively large and distinct (Parnell & Foley 2000). In V. locusta, the sterile cells are large in cross-section, intact and have a shallow, midline groove lying between them. Also, the outside (dorsal side) of the solitary fertile cell has a thick, spongy (or 'corky') outer coating; this is absent in the otherwise rather similar fruits of V. rimosa (Parnell & Foley 2000). In V. carinata, the fruits are oblong, longer than wide, and the two sterile cells have split apart to form a definite 'V'-shaped groove or trough, running along the ventral side of the fruit beneath the fertile cell. The outer wall of the fertile cell is not spongy, like it is in V. locusta (Parnell & Curtis 2012).
Another unique feature of V. dentata is that its fruits are often hairy, rather than smooth. Fruits of V. dentata and V. rimosa can be distinguished from the other two species because the calyx is (usually) clearly visible (Parnell & Foley 2000; Parnell & Curtis 2012).
Fermanagh and Irish occurrence
V. dentata has been recorded only once in Fermanagh in 1900 by Tetley, a teacher in Portora Royal School. The record was accepted and verified by Praeger (1901) for his Irish topographical botany, by which date this little summer annual was known from 33 of the 40 Irish VCs. The listing of this species is unchanged in the most recent Census Catalogue of the Flora of Ireland, yet in truth this masks a genuine decline and greatly increased rarity (Cen Cat Fl Ir 2).
V. dentata is an introduced cornfield weed of light, dry, sandy, tilled soils that has become extremely rare in the past 100 years, only just hanging on in a few sites in Ireland (An Irish Flora 1996; Flora of Co Dublin; Parnell & Curtis 2012). V. dentata is reckoned to be an ancient, accidental introduction in Ireland, and like its two relatives that also occur here, V. carinata and V. rimosa, all three are rare archaeophytes that almost never occur outside man-made habitats (Parnell & Foley 2000).
All records of V. dentata in the NE of Ireland are pre-1958 in date and, indeed, the New Atlas map shows the same is true of scattered records in the whole northern half of the island (FNEI 3; New Atlas).
A biometrical study of variation of the four Valerianella species in Ireland has shown that significant differences exist in leaf width and flower-head or partial inflorescence width (the latter measured from the base of the bracts to the furthest point of the bracts/flower head) (Parnell & Foley 2000). This has resulted in a new key to the genus in Ireland based on these characters, which requires proper field-testing.
Species decline in Britain and Ireland
V. dentata is essentially and characteristically a weed of cereal crops that grows on light, calcareous soils, particularly overlying chalk, but it can also occur locally on sand or on calcareous clay (A. Smith, in: Stewart et al. 1994). V. dentata has decreased substantially and become increasingly local in its occurrence throughout its B & I range since the earlier BSBI Atlas (Perring & Walters 1962, 1976). It is now largely confined to SE England, with only a few scattered stations in Wales and SW England (A. Smith, in Stewart et al. 1994; P.J. Wilson, in: Preston et al. 2002).
Losses appear to be down to the development of more intensive farming and especially reflect the widespread and long-term use of herbicides and the application of nitrogenous fertilisers to increasingly competitive new crop varieties.
European and world occurrence
V. dentata originates from the Mediterranean region and adjacent parts of the Middle East and it belongs to the European temperate phytogeographical element. It occurs in lowland areas throughout most of S & C Europe and stretches eastwards to Turkey and the western shores of the Caspian Sea. It is also present in N Africa. The species has spread northwards with agriculture and, in addition to B & I, has also been introduced elsewhere, for instance to Ethiopia, the W Himalaya, the Azores and the Canary Isles (Hultén & Fries 1986, Map 1738; A. Smith, in: Stewart et al. 1994).
Names
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 'dentata' means 'toothed', referring to the leaf margins.
Threats
None.
References
Parnell & Curtis 2012; Parnell & Foley 2000; Stewart et al. 1994; Hultén & Fries 1986; Perring & Walters 1962, 1976; Praeger (1901); Flora of Co Dublin; Cen Cat Fl Ir 2; FNEI 3; New Atlas; Stace (1997, 2019); Gilbert-Carter 1964; Gledhill 1985;Garrard and Streeter (1983); Webb et al (1996)