Epilobium hirsutum L., Great Willowherb

Account Summary

Growth form and preferred habitats

A common and widespread, up to 2 m tall, stoloniferous and rhizomatous, lowland, wetland perennial, the leaves of E. hirsutum are usually softly felted and are especially hairy on the veins. The robust stems are also clothed with a mixture of long, spreading, simple eglandular hairs and dense, shorter, glandular ones. As with other willowherbs, however, hairiness is extremely variable and rare almost hairless forms of E. hirsutum do exist (Clapham et al. 1962). When vegetative the plant is recognised by its height (up to 200 cm) and its opposite, unstalked, oblong-lanceolate leaves, 3-12 × 1-3 cm, the bases of which run a short way down the stem forming wings on it (Sell & Murrell 2009).

'Great Hairy Willowherb', to give the plant its most descriptive English common name, often forms tight, vigorously growing, tall, clonal patches which can become locally dominant in lowland, sheltered, damp to wet, moderately acid to lime-rich ground of reasonable fertility (Kitchener 1992a). In the Sheffield area, Grime et al. (1988, 2007) described its ecological established strategy as a definite 'Competitor' and found that it avoided strongly acid conditions (pH below 4.0), preferring those above about pH 6.0 to neutral, which fits well the observed behaviour in Fermanagh. Much less frequently, it occurs in shallow standing water of mesotrophic to eutrophic productivity and equivalent nutrient status.

In parallel with its smaller, less aggressively competitive relative E. parviflorum (Hoary Willowherb), E. hirsutum also grows and persists on relatively dry roadside banks and occasionally in waste ground, including in old quarries and sand- and gravel-pits. However, it inhabits these drier habitats much more rarely than it appears in wetland situations, such as in ditches, on streamsides and lake shoreline tall-herb fens and marshes. While definitely a wetland species, E. hirsutum performs less well in permanently wet fens and marshes than on periodically flooded waterside ground (Grime et al. 1988, 2007).

E. hirsutum is intolerant of grazing or mowing and is quickly replaced by lower growing species under such circumstances (Grime et al. 1988, 2007).

Fermanagh occurrence

E. hirsutum has been recorded in 260 Fermanagh tetrads, 49.2% of those in the VC. As the tetrad map indicates, it is very common and widespread around both parts of Lough Erne and is widely scattered in many other suitable lowland, wet to damp ground sites throughout the county. As such E. hirsutum is considerably more frequent and widespread than E. parviflorum and it just beats the very much smaller, calcifuge wetland species, E. palustre, in terms of both frequency and distribution statistics.

Great Willowherb tolerates semi-shaded conditions in both fen-carr and on the margins of damp deciduous woods. There are numerous records of the latter in Fermanagh, including, for instance around many of the wooded isles and along the shores of Lough Erne, plus in the upland Correl Glen NR mixed deciduous woods on the Western Plateau, Marlbank Wood, above Florencecourt and in fairly steep broken limestone rocky ground in the steeply sloping Hanging Rock NR.

Reproduction

Since it dies down completely each autumn, regrowth of Great Willowherb begins in early spring. Being a large, robust, stand-forming plant, a prolonged vegetative period is required before the very numerous, large, soft purplish-pink, insect-pollinated flowers can be produced. They are borne on long, branched, corymbose, inflorescences from late July into August, and are terminal on main stems and branches. White flowered plants are very occasionally encountered and have been given the name var. hirsutum forma albiflorum Hausskn. in Sell & Murrell (2009).

The flowers are protandrous and pollination is carried out by bees and hoverflies. Flowering reproduction is extremely effective, vast quantities of plumed seed being released on the wind by the splitting of the 5-8 cm long, linear fruit capsules. The seed is long-persistent in the soil.

Additional vegetative reproduction takes place by the spreading growth of fleshy, white underground rhizomes or leafy surface stolons in the autumn and winter (Grime et al. 1988, 2007). Thus by one of these means, the species can readily colonise freshly available, reasonably undisturbed, ungrazed sites, eg in quarries (Shamsi & Whitehead 1974, 1977).

Hybridization

In B & I, E. hirsutum rarely or very rarely forms hybrids with six other willowherb species, none of which have ever been found in Fermanagh (Sell & Murrell 2009).

British and Irish occurrence

In Ireland, E. hirsutum is common, widespread and sometimes dominant except in the more acidic bog soils of the far west. It is also common and widespread in Britain, except in Scotland where it becomes coastal northwards. These facts suggest that low winter temperatures and acidic soils are factors limiting its distribution (Preston et al. 2002).

European and world occurrence

A native of southern-temperate Eurasia, E. hirsutum has naturalised widely elsewhere, including in eastern N America and C & S Africa (Hulten & Fries 1986, Map 1357).

Threats

None.

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