Viola palustris L., Marsh Violet
Account Summary
Native, common and locally abundant. European boreo-temperate, but also present in eastern N America.
1806; Scott, Prof. R.; Co Fermanagh.
March to November.
Growth form and preferred habitats
V. palustris is the only violet in B & I that produces long, slender, creeping rhizomes that bear rather large, broad, almost circular, cordate or reniform, hairless stem leaves in rosettes of 1-4 on very long petioles (stalks). The leaves start pale green and darken as they age and they continuously enlarge throughout the growing season, from around 2.0-4.0 cm across during spring flowering up to 7 cm or more later in the summer. They are hairless (glabrous) and the leaf margin bears very shallow, blunt teeth. The creeping stems also bear flowers on individual stalks that are pale blue, pale lilac or white, the lowest petal being streaked with purple veins (Porter & Foley 2017).
V. palustris occurs over a wide altitudinal range in wet, acidic soils in bogs, damp heaths, marshes and swampy woodland including alder and scrubby willow and birch fen-carr, especially beside little runnels and where the typical peaty or clayey substrate is flushed by groundwater springs. In wet woods and scrub it thrives in partial shade. Marsh Violet is often found growing through spongy cushions or carpets of Sphagnum moss and on account of its creeping mode of growth and single blossom per flower stalk, it cannot, or only very rarely, flowers in profusion.
In coastal regions of B & I it can sometimes be found in non-calcareous dune slacks. However, the preferred wet, acid habitat conditions are most frequently met in northern and western parts of these islands (New Atlas). Previously, V. palustris was also a common component of species-rich fen meadows, but it has declined in this particular habitat during the last 50 years, particularly in S & E England and also in C Ireland where it was never very common. The decline in the species follows major changes in land use, including long-term peat cutting for fuel on bogland, plus drainage of marshes and wet fields and the ploughing and reseeding of meadows as part of agricultural intensification on lower slopes and hollows taking place over the last 50 years or so.
Studies using American species have shown that predation (ie herbivory and seed destruction) and insufficient soil moisture, tend to be the most frequent causes of death in violet populations. However, long persistence in the soil seed bank is a characteristic feature of this genus and is a very successful adaptation to uncertain environments, permitting re-emergence of the species if and when more suitable growing conditions return (Cook 1979, 1980, p. 126).
Fermanagh occurrence
Locally, V. palustris is common and has been recorded scattered across 152 Fermanagh tetrads, 28.8% of the VC total. It is widespread in peaty areas throughout Fermanagh, but is especially common around the southern half of Upper Lough Erne and on the slopes and summit plateau of Cuilcagh mountain.
Flowering reproduction
The small spring flowers, which appear from April through to June or July, open in the normal manner for cross-pollination by insect visitors, although they produce no scent to attract them (Hutchinson 1972). Like other species in subgenus Viola, V. palustris also produces small, closed, bud-like, self-pollinated cleistogamous flowers later in summer and early autumn. Both flower types shed seeds, but unlike most members of the genus they either do not bear elaiosome food bodies (or only very small ones), since ants do not frequent boggy ground (Clapham et al. 1962; Jonsell et al. 2010).
V. palustris has also become regionally endangered in some other European countries. Recent experiments in an abandoned fen meadow in NW Germany showed that V. palustris recruitment and growth in damp fen-grassland conditions is promoted by a regular disturbance regime, ie by moderate degrees of grazing or cutting. Sinker et al. (1985) had also noted that the species is fairly tolerant of grazing and trampling in the Shropshire region (VC 40). This form of management prevents successional changes which lead to an increase in standing crop (ie the development of rank, dense, taller vegetation) and the development of a deeper litter layer clothing the soil surface. Both these factors can oust V. palustris through suppression of seedling recruitment and excessive competition for light and other survival essentials (Jensen & Meyer 2001).
Vegetative reproduction
It should be remembered that many perennial violets including V. palustris also reproduce effectively by vegetative growth and spread of above-ground stolons, or of the subterranean rhizome. This provides perennial violets with a pattern of growth and increase which Bell & Tomlinson (1980) recognised as "opportunistic". Horizontal stem growth is indeterminate in terms of stolon numbers, distance (ie stolon length) and direction.
European occurrence
Beyond our shores, elsewhere in Europe, V. palustris is widespread in northern temperate latitudes from S Greenland to Scandinavia and it stretches southwards to Spain and Portugal, N Italy and Bosnia, plus the mountains of Morocco and the Azores (Hultén & Fries 1986, Map 1333).
World occurrence
It is present in N Africa and eastern N America, although it is still unclear whether or not the plant present in the latter is V. palustris (Hultén 1958, Map 103), or the closely related (and also Amphi-Atlantic) V. epipsilla Ledeb., of which there are two subspecies (see Hultén 1958, Map 104 and Hultén & Fries 1986, Map 1334 and p. 1093). If we combine the ranges of these two species to form V. palustris sens. lat., the combination would then be almost circumpolar (for a discussion of the problem, see Hultén 1958, p. 122).
Name
The Latin specific epithet 'palustris' means 'growing in swampy places' (Gilbert-Carter 1964).
Threats
Habitat changes favouring secondary succession, leading to competitive exclusion or burial by plant litter or overgrowth.