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Moehringia trinervia (L.) Clairv., Three-nerved Sandwort

Account Summary

Native, occasional, but possibly somewhat over-looked. European temperate, also native in parts of W & E Asia and N Africa.

1881-2; Barrington, R.M.; Co Fermanagh.

March to September.

Growth form and preferred habitats

Despite the specific epithet, 'trinervia', the relatively large ovate leaves of this annual Sandwort have three or five unbranched, almost parallel veins and ciliate margins, which are very obvious and distinctive when held up to the light. At first glance the species is rather similar in appearance to large plants of Stellaria media (Common Chickweed), but its most distinctive habitats in open spots in shady, often damp, glades in deciduous woods and the bottom of hedges, are usually less disturbed than the typical conditions occupied by the latter very common weed.

M. trinerva is found in other shaded situations, for instance on cliffs and rock terraces (ledges) and outcrops, and on disturbed mineral soil (Grime et al. 1988, 2007). In coastal regions, it can occupy heaths, pastures and seashore habitats, very probably always lacking shade. The same may be said for a range of man-made, apophytic habitats, including roadsides, lawns, path and field margins, gravel-pits and ruderal ground generally (Jonsell et al. 2001). In Cardiganshire, Wales (VC 46), Chater (2010) recorded M. trinerva growing in shade under Pteridium aquilinum (Bracken) near the coast, and far more surprisingly, on wall tops completely exposed to both light and weather!

While often found tolerating dry situations, the preferred substrate of the species is moist, yet well-drained, fertile, often nitrogen-rich, weakly acidic to neutral soils that are subject to sufficient disturbance to keep bare ground available for colonisation by seed. It is mostly found in vegetation where the environment provides moderate intensities of both stress and disturbance.

Behaviour in woodland

M. trinervia is one of the very few native annuals that we might call a true denizen of woodland shade, a habitat very much dominated by slow-growing perennials and biennials. The main problem for an annual species living in shade conditions is to grow fast enough to complete its life-cycle, since without a fresh crop of seed it cannot perpetuate itself (Fitter 1987).

Although M. trinervia usually behaves as a summer annual, very occasionally, when growing under shallower depths of shade, individual plants manage to survive the effort of flowering. When this happens they become relatively short-lived polycarpic perennials, a change that helps the individual overcome the shade survival hurdle for annual species. Despite this flexibility in reproductive strategy, M. trinervia still relies entirely on seed for its reproduction, there being no vegetative means of increase or dispersal available to the plant (Grime et al. 1988).

As with other small, diffusely branching annuals, populations often perform best on warm, sparsely vegetated slopes under trees or shrubs – including sometimes evergreen species like Ilex aquifolium (Holly) (Garrard & Streeter 1983). Another reason for growing on slopes is the likelihood that, thanks to gravity, leaf litter will not be present, or be deep enough to prevent establishment of a small, weakly competitive annual species. M. trinervia is a poor competitor with other more vigorous herbs of woodland or shade-tolerant situations, and thus is often confined to moderately disturbed or unstable ground, such as near rabbit burrows or fallen trees (Sinker et al. 1985; Grime et al. 1988, 2007).

Being something of a nitrophile, M. trinervia sometimes grows under or near nettle patches, or becomes associated with Galium aparine (Cleavers) (Clapham et al. 1987; Crawley 2005). The level of disturbance in woodland plantations provided by modern mechanical forestry operations favours the growth of M. trinervia, and this form of human disturbance probably also serves to assist dispersal of the species. Three-nerved Sandwort has benefitted from logging sites, the construction of forest roads and in general all human activity that disturbs woodland. However, despite this it is not really a plant that favours human activity, unlike Common Chickweed, with which it is often confused.

Flowering reproduction

The small, solitary flowers produced in May and June bear white petals that are much shorter than the sepals. The flowers are visited by small flies and crawling insects such as beetles, although they will automatically self-fertilise if not visited. Fruiting occurs and seed is shed in June and July. The number of fruit capsules per plant varies enormously: Salisbury (1942) reckoned the range of capsules produced lies between 51 and nearly 6,000, with a mean of about 200 (NB Salisbury calls the species Arenaria trinervia, p. 227). Seeds per capsule range from four to 17, and therefore the computed mean seed production is around 2,500 per plant (Salisbury 1942).

Seed dispersal

Seeds are shiny, kidney-shaped, black and have an attached highly nutritive white food body – an elaiosome oil appendage – that attracts ants. The ants help disperse seed from around the parent plant, thus minimising seed predation (Clapham et al. 1987). Longer range dispersal of seed in mud attached to animals, including man and his machinery, is undoubtedly also significant.

Seed survival

There are 15 estimates of seed persistence of the species in the survey of soil seed-banks of NW Europe. Five samples indicate that M. trinervia can at best be considered short-term persistent in the soil, ie they display dormant survival of more than one and less than five years (Thompson et al. 1997).

Variation

A modest range of variation occurs within M. trinervia with respect to plant habit, colour and hairiness, most or all of it associated with local environmental conditions and the season of seed germination (Hind 1985).

Fermanagh occurrence

In Fermanagh, M. trinervia has been occasionally recorded from a total of 35 tetrads, 6.6% of those in the VC. As the distribution map indicates, about half its stations are scattered around the moist, wooded shores of both parts of Lough Erne, with the remainder thinly and widely spread across the county. It is not a conspicuous plant and is often only present as scattered individuals. It is therefore very probably under-recorded.

British and Irish occurrence

In Britain, the species, as shown in the New Atlas hectad map, is widespread in most lowland areas, except the English Fens and the Wash. It becomes rare and coastal further N & W in Scotland – a familiar enough distribution pattern. In Ireland, by comparison with Great Britain, the distribution is very much patchier. Whether or not this is an artefact of recorder effort or possible unawareness is not clear from this evidence, but under-recording remains a definite possibility. The more comprehensive recording of the species in the three Cork VCs is rather striking, and itself lends support to this contention. Again, in NI, there appears to be more records of this Sandwort in the broad basins of Lough Neagh and Lough Erne, perhaps because these two areas have been exhaustively and systematically surveyed in recent years (Preston et al. 2002).

European and world occurrence

More or less restricted to Europe and thinly scattered parts of W Asia and N Africa, although also present in the Canaries. An isolated population in far eastern Asia (Japan), distinguished as M. platysperma Maxim., is said by Hultén & Fries (1986) to be identical with the European taxon. If this is really so, then it constitutes a major discontinuity in the distribution of this species, and probably arose from a case of accidental introduction.

Names

The genus name 'Moehringia' is called after Paul Heinrich Moehring (1720-1805) a physician and naturalist at Jever in Oldenburg, Lower Saxony, N Germany (Gilbert-Carter 1964). The Latin specific epithet 'trinerva' means 'three nerved', referring to the three (or up to five) prominent veins observed in the leaves.

Threats

None.