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Epilobium palustre L., Marsh Willowherb

Account Summary

Native, frequent. Circumpolar boreo-temperate.

1900; Praeger, R.Ll.; Co Fermanagh.

May to November.

Growth form, identification and preferred habitats

E. palustre is a stoloniferous perennial herb, 15-60 cm tall, with leafy, terete (cylindrical), pale green stems rising erect from a curved base (Sell & Murrell 2009). E. palustre can easily be confused with several other Epilobium species and perhaps most easily with E. obscurum (Short-fruited Willowherb). However, E. palustre is distinguished from all other willowherbs that possess a club-shaped stigma, by the absence of raised ridges on the stem, although there may be two lines of hairs (Kitchener 1992b). For other identification points separating members of this willowherb group, see the E. obscurum account above.

This calcifuge willowherb occurs at all elevations, almost right up to the summit of Cuilcagh, the highest mountain in Fermanagh. It can grow on a wide range of usually base-poor, but occasionally flushed, damp to wet, acid to neutral soils. Marsh Willowherb can also occasionally be found in limestone areas, but it then appears confined to pockets of leached, acid soil, or in ground where patches of glacial drift overlie and bury calcareous bedrock.

In common with other primarily wetland willowherbs, the range of habitats occupied by Marsh Willowherb is extremely wide. It includes damp peat bogs, either cut-over, flushed, or neither of these, plus swampy and marshy lakeshore grassland, muddy bare ground or short sedge fen. However, E. palustre is not an aquatic species and it shuns both exposure on the margins of open water and shading from tall-herb fen or dense fen-carr environments. It can, however, tolerate semi-shade on woodland margins or in clearings and it very often features as a pioneer species in open, fully-illuminated sites on track sides, ditch margins and stream sides of all dimensions.

As with other willowherbs, E. palustre can also colonise rather drier situations than it normally frequents, occupying open disturbed ground on wasteland, roadsides, disused quarries or sand- and gravel-pits. In upland areas, Marsh Willowherb can occur, in addition, on cliff ledges and on wet rock outcrops. In every situation and on all occasions, it avoids competition from more vigorous, taller, aggressively crowding plant species. This is why the established strategy of E. palustre is described as intermediate between C-S-R and Stress tolerator by Grime et al. (1988, 2007). However, it is important to bear in mind that this ecological determination is based to a considerable extent on the species' ability to garner nutrients from the environments it occupies, and E. palustre tolerates an unusually wide range of habitats and demonstrates a range of strategies to cope with different ecological niches (Craine 2009).

While Marsh Willowherb cannot survive heavy or regular disturbance in the form of grazing, cutting or trampling, it is favoured by moderate levels of these and other growth limiting factors which help prevent potential dominant species ousting it. At the same time, it tends to occupy soils of intermediate fertility and moderate pH, rather than the extremes (Sinker et al. 1985; Grime et al. 1988, 2007).

E. palustre overwinters both as dormant seed and as small, tight, terminal buds on the ends of thread-like underground stolons emanating from the base of the old plant. This is an important distinguishing character from the recently arrived and now widespread American alien, E. ciliatum (American Willowherb).

Fermanagh occurrence

In terms of its frequency and distribution statistics in Fermanagh, E. palustre trails E. montanum (Broad-leaved Willowherb) by a wide margin, but it more closely matches figures for the very much larger species, E. hirsutum (Great Willowherb). Nevertheless, E. palustre is still the third most frequent and widespread willowherb in Fermanagh, being present in 254 tetrads, 48.1% of those in the VC. While it is well scattered throughout Fermanagh, E. palustre is somewhat more prevalent around Upper Lough Erne and on the Western Plateau.

Flowering reproduction

E. palustre flowers in July and August, the inflorescence consisting of a loose raceme of just around ten small, mauvish-pink flowers, 4-6 mm in diameter. The flower buds are initially erect but soon droop, so that the whole raceme hangs over to one side and the flowers are held almost horizontally. The flowers are perfect (ie hermaphrodite), homogamous (male and female ripen simultaneously) and they usually self-pollinate. Seed is set from July to September – the fruit capsule being green, flushed crimson, 5-8 cm long and splitting to release numerous, small, lightweight, plumed seeds that are wind-dispersed (Ross-Craig 1948-1973, Part XI Plate 27; Grime et al. 1988, 2007; Sell & Murrell 2009).

Vegetative reproduction

In summer, filiform (thread-like), often but not always subterranean stolons bearing distant pairs of yellowish scale-leaves and terminating in autumn in swollen, bulbil-like buds with fleshy scales (ie turions), develop from the base of the aerial plant, providing the over-wintering mechanism of E. palustre. These bulbils or turions give rise to new plants in the springtime, often at up to 10 cm from the original parent plant. Detached turions and portions of stem may also play a part in vegetative spread of the species in some of its more disturbed habitats, for instance being carried away in flood waters (Grime et al. 1988 & 2007; G.D. Kitchener, in: Preston et al. 2002).

Seed longevity

Thirteen studies examined in the survey of NW European soil seed banks gave mixed results and no clear indication of buried seed longevity (Thompson et al. 1997). Six of the studies found seed persisted less than one year, three reported that they survived between one and five years, and one considered them long-term persistent (at least five years). Three studies could not assign them to any of these categories.

Most members of this genus have a proportion of their seed capable of surviving for more than one year although others, like E. hirsutum and E. obscurum, have long-persistent seed buried in the soil that can survive five or more years.

British and Irish occurrence

E. palustre is widespread and locally common throughout B & I, but has significantly declined in SE England, mainly since 1950, most probably due to drainage and eutrophication associated with agricultural intensification (G.D. Kitchener, in: Preston et al. 2002).

European and world occurrence

E. palustre is widespread in Europe northwards to Iceland and Lapland. It becomes more scattered and scarce towards the Mediterranean. It is also widely distributed in Asia, N America and Greenland, making it Circumpolar Boreo-temperate (Hultén & Fries 1986, Map 1365).

Hybrids

It is capable of hybridising with numerous other willowherb species (eg E. alsinifolium (Chickweed Willowherb), E. brunnescens (New Zealand Willowherb), E. montanum (Broad-leaved Willowherb), E. obscurum (Short-fruited Willowherb), E. parviflorum (Hoary Willowherb), E. roseum (Pale Willowherb) and E. tetragonum (Square-stalked Willowherb)), but they are all of rare occurrence in Britain, and either extremely rare or absent in Ireland (Stace et al. 2015). Also put in alpha

Threats

Eutrophication of water bodies and soil nutrient enrichment generally, could well stimulate competition and oust this species.

Epilobium brunnescens (Cockayne) P.H. Raven & Engelhorn, New Zealand Willowherb

Introduction, neophyte, a frequent garden escape now well naturalised.

1940; Faris, R.C.; Benaughlin.

Throughout the year.

Growth form and introduction

A low-creeping, small-leaved, prostrate, mat-forming perennial with often almost unopened, insignificant looking, solitary pinkish-white flowers produced on relatively long stalks, E. brunnescens was first recorded in the British Isles as a garden weed in Edinburgh in 1904, and as a naturalised plant in a disturbed, non-garden situation in Wiltshire in 1908 (Davey 1953). It made its first published naturalised appearance in Wales as late as 1930 (Harrison 1968), and did not appear in Ireland until 1932 (Brunker 1950), even though Nelson (1994) has uncovered evidence that Irish nurserymen were selling it to gardeners as a rockery plant in the early 1900s. Apart from this deliberate introduction, E. brunnescens very probably also arrived in B & I accidentally. Seed could easily have been transported in soil on the roots of imported New Zealand trees, shrubs, alpines and other garden plants, many of which are popular and grow very successfully here.

In common with the pattern of other introduced species, after an initial delay, E. brunnescens, which seeds itself freely, entered an 'explosive phase', spreading very rapidly from numerous localised focal points. As a result it is now widely distributed and frequent to locally abundant in northern and western parts of B & I at elevations from sea-level to high mountain summits, preferring the higher ground (Davey 1961; New Atlas).

Preferred habitats and ecology

The plant has a shallow fibrous root system penetrating only 6 cm at most, a limitation which makes it require either an almost permanently damp, although well-drained gritty, sandy or stony soil, or an otherwise drought-protected substratum. Thus although the plant is a wintergreen perennial, spreading and forming low, clonal mats by means of frequent branching and rooting at leaf-nodes, individuals are susceptible to drought and may be killed if it is severe or prolonged (Davey 1961). This undoubtedly helps explain why the species is scarce or absent from most of the E, SE and Midland counties of England which regularly experience high summer temperatures and droughts that would be lethal to this species (Preston et al. 2002). This explanation does not cover the similar scarcity of E. brunnescens in C Ireland and, at present, the current author (RSF) is unable to supply a logical explanation.

E. brunnescens occurs on various types of soil, both acidic and lime- or base-rich, always provided they are sufficiently damp, free-drained and the habitat open to seed colonisation (Davey 1953, 1961; Harrison 1968). The habitat openness requirement for establishment frequently involves a modest degree of substrate and vegetation disturbance, either through natural instability of the site, or human involvement, eg trampling or grazing by stock. While typically found in fully illuminated conditions, the species can tolerate some degree of shade, for instance along woodland paths or in ditches, or from older ericaceous shrubs (Davey 1961). The plant is regularly found in close association with other similar low-growing or creeping species, eg Lysimachia tenella (Bog Pimpernel), Chrysosplenium oppositifolium (Opposite-leaved Golden-saxifrage) and Sagina procumbens (Procumbent Pearlwort) and various mosses including Sphagnum species. Care is then needed in its identification, since non-flowering specimens of the species might easily be confused with Lysimachia tenella.

Reproduction

Although limited vegetative spread does occur (ie local diffusion as a result of horizontal growth), drought sensitivity makes the species very dependent on seed for both population maintenance and dispersal. The numerous solitary flowers, produced over a prolonged period from April or May through to November, are almost always self-pollinated (but see below), often in bud or in the unopened flower. They are self-fertile and the abundant tiny seed (c 120 per capsule) thus produced are equipped for efficient wind dispersal with the tufted plumed pappus typical of the seeds in this genus (Davey 1961). Germination can occur after only a fortnight, but late autumn seedlings seldom survive while those produced in early spring have the capacity to flower later the same season (Davey 1961). The current author (RSF) has not found any information regarding seed bank longevity, except that Davey (1961) reported no germination in seed after 17 months storage.

Fermanagh occurrence

E. brunnescens is frequent, widespread and is probably still actively spreading in Fermanagh, having been recorded from 87 tetrads to date, 16.5% of those in the VC. It has even reached the summit of Cuilcagh, the highest mountain in Fermanagh – a decidedly remote situation that is not all that frequently visited.

Hybrids

Hybrids between E. brunnescens and no less than five other species of willowherb have been recognised from various parts of B & I, proving that cross-pollination in the wild clearly occurs. Irish hybrid material involved originates from Cos Antrim (H39) and Tyrone (H36), and comprises of crosses with alien E. ciliatum (American Willowherb) and native E. obscurum (Short-fruited Willowherb) (Kitchener & McKean 1998).

Name

The Latin specific epithet 'brunnescens', means 'approaching brown', ie tending to become brown or brownish, but implying not attaining full development of that colour; a reference to the leaf colour (Stearn 1973).

Threats

There are no threats to it and while E. brunnescens is a frequent and widespread relatively recent introduction, especially in upland sites, it appears to co-exist with native species rather than oust them.

Chamaenerion angustifolium (L.) Scop. (= Epilobium angustifolium L., Chamerion angustifolium (L.) Holub), Rosebay Willowherb

Native, frequent and widely scattered throughout. Circumpolar boreo-temperate.

1904; Praeger, R.Ll.; western end of the Cliffs of Magho.

Throughout the year.

Growth form and preferred habitats

A very tall, leafy herbaceous perennial, 1-3 m in height, with a combination of long, horizontally spreading and deeply penetrating roots. Stems can be either simple or branched and are glabrous below and hairy above. Leaves are alternate, spirally arranged, 5-20 × 1.0-3.5 cm, oblong-lanceolate in shape with margins entire or with small, distinct horny teeth. The leaf margin is also often wavy and the base is narrowed and either sessile or obscurely petiolate. Shoots die back completely in autumn, buds on the old stem base overwintering and giving rise to new aerial shoots in spring. A strongly competitive species with high mineral nutrient requirements, it often forms large, dominant clonal patches under a wide range of usually ± fertile (ie nutrient-rich, well-aerated and favouring nitrification) disturbed conditions (Myerscough & Whitehead 1966; Grime et al. 1988 & 2007; Broderick 1990). It is rarely found in long-established plant communities, being more characteristic of disturbed, neglected derelict land (Myerscough 1980).

The history of its spread

In Praeger's prime recording days (the late 1880s to the early decades of the 20th century), this species was recognised primarily as a plant of mountain cliff ledges and rocky gullies, chiefly confined to the north of both B & I. By the mid-1940s, however, it effectively modified its tolerances and had already colonised a variety of once-disturbed lowland habitats. While this tall-growing species is now a pioneer, rapidly invading recently disturbed ground, it cannot survive regular, continued disruption in the form of trampling, grazing, cutting or burning (Myerscough 1980). Suitable fresh sites often involve major works of vegetation clearance and an extensive exposure of bare soil or burnt ground, eg in clear-felled or wind-thrown forestry plantations, major roadworks, building or bomb sites, or where land has been recently reclaimed from scrub invasion.

Having successfully colonised and established numerous new, sometimes dense, dominant populations in this range of disturbed lowland sites, C. angustifolium then used these foci to colonise a further series of often much smaller patches of disturbed, burnt or droughted ground, in a very wide variety of soil types. The soils range from wet mud to rather dry sand and from acid to fairly alkaline (Myerscough & Whitehead 1966; Myerscough 1980; Broderick 1990). This later more 'weedy' colonisation was much less aggressive and more gradual in Ireland than was the case in Britain, so that Webb (1972) was only then reporting the plant's recent arrival in parts of central Dublin.

Reproduction

In unshaded conditions, C. angustifolium flowers from July to September. The inflorescence is a long, spike-like raceme, often bearing up to 200 bisexual, perfect, purple flowers, 20-30 mm in diameter. The inflorescence size generally indicates the reproductive investment the plant can afford. The flowers are protandrous and can self-pollinate, although they do also attract insect visitors (mainly bees) for pollination (Schmid-Hempel & Speiser 1988). Nectar is secreted by the epigynous disk at the base of the style (Clapham et al. 1987). Thanks to the height of the plant (0.5-3 m), species mobility is conferred by the considerable output of well-plumed, airborne seed, released from long capsules frequently 200-250 cm above the ground.

It has been shown, however, that once established in a site and having developed a ± dense population, C. angustifolium plants direct a very high proportion of their photosynthetic resources into vegetative growth and horizontal root or rhizome spread, rather than towards flower and seed production (van Andel & Rozema 1974; van Andel & Vera 1977).

Having a very extensive underground network of rhizome and mycorrhizal fibrous roots, the plant is an effective accumulator of mineral nutrients after forest fires and has a conservative system of internal mineral recycling within the root and shoot (van Andel & Nelissen 1979). The extensive annual shoot litter is also rapidly recycled, while the root system of existing stands appears to inhibit its own seed germination (van Andel & Rozema 1974). These properties enable dense colonies to persist for 30 or more years and individual root segments can survive for up to 47 years, and perhaps much longer (van Andel 1975; Broderick 1990).

Species native status

The suggestion that the C. angustifolium population that spread so noticeably in the 20th century was alien rather than native was not supported by morphological, genetic and cytological studies (Myerscough 1980). Molecular genetic tests have yet to pronounce a verdict on this question.

Fermanagh occurrence

Consequent to all this, as the tetrad map shows, C. angustifolium is now widely scattered across 162 Fermanagh tetrads, 30.7% of those in the VC. It occupies a range of weedy, ruderal habitats, including quarries, roadside banks, urban waste ground, the unmanaged rough ground margins of bogs and car-parks, and it can even grow and survive to flower on damp walls.

British and Irish occurrence

C. angustifolium is common, widespread and often abundant over most of B & I, except for the far west of Ireland and in patchy areas of NW Scotland including the islands (Preston et al. 2002).

European and world occurrence

A completely circumpolar species (Circumpolar Boreo-temperate element), C. angustifolium occurs across Eurasia and N America from 25oN to within the Arctic Circle. It is a more recent introduction in some parts of its range and, for instance, has now been recorded in N Africa. In Europe, it is widespread and generally common in the north, but is more scattered and rare in the south (Myerscough 1980; Hultén & Fries 1986, Map 1355; Sell & Murrell 2009). In the more southern part of the species distribution, Hultén & Fries (1986) separate off subsp. circumvagum Mosquin, mainly in N America, and Myerscough (1980) follows this decision.

Threats

None.