Northern Ireland's Priority Species

Salix myrsinifolia – dark-leaved willow

Salix myrsinifolia

Salix myrsinifolia Salisb.
Family: Salicaceae

The problems involved and labour required in identifying willows has meant that the group is often shunned by botanists and the recording of this species has had a chequered history in Northern Ireland. It was first recorded in Ireland by John Templeton in the Braid Valley of County Antrim in the early nineteenth century, but then not again until the 1980s when it was rediscovered in the hills and glens of Antrim, together with hybrids between it and other willow species, by John Harron.

In brief

  • Often ignored, and not recorded in Northern Ireland for much of the twentieth century
  • Grows mainly along river and stream sides in Counties Antrim and Londonderry
  • Its round leaves are obvious throughout the summer
  • Northern Ireland hosts a very significant proportion of the Irish population
  • Has been disappearing from parts of Antrim.

Species description
This willow varies in stature from a low sprawling shrub less than 1m tall, to a small tree up to 3m tall. Shrubby and tree-like willows can be divided into narrow-leaved and wide-leaved types. Dark-leaved willow (Salix myrsinifolia) is included in the latter group known as ‘Sallows’. It has distinctly rounded leaves and stipules (small paired leaf-like projections where the leaf stalk joins the twig) that blacken when pressed. A property acknowledged by its former scientific name Salix nigricans. Flowers are the typical silky willow catkins sometimes called ‘pussy-willows’.

Life cycle
As in all willows, male and female flowers appear as catkins on different plants. In this species the catkins appear along with the young leaves in April / May and even quite young trees are fertile. Pollination is mainly by insects which must visit first male, then female, plants, so both sexes have nectaries. Each flower is in the scale axil of a catkin. Male catkins are lost in the spring, but even infertile female catkins persist through the summer. Fertile seeds have a ring of cottony hairs at the base which in dry weather expand and help push them out of the split seed capsules, and then can act as a fluffy parachute to carry the seed off in any breeze. The tiny seeds are only viable for a short while and if it is to germinate it must land in a damp seedbed soon after its release. The bark and leaves are bitter if chewed; this is because of tannins and particularly high levels of salicin, a precursor of the drug aspirin. These are a defence against herbivores.

Similar species
Willows in general are a challenging group to identify and cause problems even for most botanists because they are morphologically variable, they hybridise readily with other willows often to form fertile offspring that themselves can hybridise again; there are a number of cultivated varieties characteristics of which have found their way into the ‘gene pool’, and because for many species both flowers and mature leaves are required — alas, these are not present on a tree at the same time.

It most resembles tea-leaved willow (Salix phylicifolia), another rare species (some authors have recommended that they be lumped together as a single species); however, tea-leaved willow has yet to be recorded in Northern Ireland so here, dark-leaved willow is more likely to be overlooked as a form of rusty willow (Salix cinerea) or eared willow (Salix aurita) which are our most common willows, being widespread and abundant in many habitats. Hybrids between the dark-leaved and rusty willow (Salix x strepida) have been identified over most of the Northern Irish range of dark-leaved willow. The roundness of the leaves, their dark colour, and persistent and obvious rounded stipules are all indicators of tea-leaved willow. If pressed, dark-leaved willow leaves always darken to almost black, (though leaves of almost any willow species are prone to do so) and bruised leaves blacken rapidly.

How to see this species
The best time to look for this species is in the summer when the leaves are mature. It grows in a variety of habitats including woodlands, hedgerows and wetlands, but especially along stream banks, it is not normally thicket forming but occurs as occasional specimens scattered here and there. It is a hard species to identify with certainty, and finding a specimen that is ‘myrsinifolia-ish’ may be the more advisable ambition for the non-specialist. The Linford and Skegh valleys in Upper Glenarm, County Antrim is where it occurs in most abundance in Northern Ireland, but mainly as hybrids. The pure species is more likely to be found in the Roe Valley, County Londonderry. Though not the most decorative of willows, cultivated varieties of this species are available from nurseries and can be seen in landscape plantings.

Current status
Its natural range in both Britain and Ireland is essentially northern, but whilst it is widespread in Scotland and the north of England, it is apparently of very restricted occurrence here. Outside the counties of Antrim and Londonderry there are only very scattered sites from which the species has been recorded, and in these there is some suspicion that it may be introduced. In the Republic of Ireland it has been recorded from the border counties Cavan, Monaghan, Donegal and Louth, (as well as Westmeath). It is perhaps surprising that it has not yet turned up in Counties Armagh or Fermanagh.

It also is found in northern European countries extending into Russia, and in a few more southerly European countries where it is restricted to mountainous areas and thought to be decreasing.

Why is this species a priority in Northern Ireland?

  • Decline and scarce — confined to a small population of one or two locations in Northern Ireland with Northern Ireland being a stronghold consisting of over half of the Irish population.

This applies particularly to the pure species found in the Roe Valley.

Threats/Causes of decline
This species has apparently disappeared from several locations in County Antrim. It is vulnerable to scrub clearance, especially associated with river engineering/maintenance projects.

Conservation of this species

Current action

  • The Owencloghy / Glenarm rivers are designated ASSIs and include populations of this species and its hybrids.

Proposed objectives/actions

  • Maintain the number of viable populations of the species
  • Maintain the range of the species.

What you can do
When visiting riverbanks or lake shores in Northern Ireland, keep an eye out for small, round-leaved willows with leaves that bruise easily. These could be dark-leaved willow. If this species is suspected, make a careful note of the location of the shrub and remove a small spray of leaves for pressing and sending to the Ulster Museumís botany department. Final confirmation may depend upon a re-visit in spring.

Further information

Information on ASSIs

Flora of Northern Ireland

Harron, J. (1992). The present distribution of the dark-leaved willow Salix myrsinifolia Salisb. in north-east Ireland. Irish Naturalistsí Journal 24: 8-11.

Howitt, R.C.L. and Howitt, B.M. (1990). Willows. In: A guide to some difficult plants: Illustrated Articles from the Wild Flower Society Magazine 1973-1988. The Wild Flower Society.

Meikle, R.D. (1984). BSBI Handbook No. 4: Willows and Poplars of Great Britain. BSBI, London.

Text written by:
Shaun Wolfe-Murphy