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Myrica gale L., Bog-myrtle

Account Summary

Native, frequent and fairly widespread in upland, acid terrain. Suboceanic boreo-temperate, also in E Asia and N America.

1881; Stewart, S.A.; Co Fermanagh.

Throughout the year.

Growth form and preferred habitats

Generally a small, much branched, deciduous shrub with oblong-obovate leaves, 2-6 cm long, under ideal conditions Bog-myrtle can grow up to 2.5 m tall, although usually it reaches only 1.5 m in height. The shrubs are grazed by sheep, goats and hares and on occasions may be reduced in height to 50 cm or less by such pressure. Twigs and leaves are covered with yellowish, resin glands and crushed leaves give off a pleasant resinous fragrance. When crushed and rubbed on skin they are very effective in keeping midges away, a tip worth remembering when walking or working on bogs in summer. Midges are paralysed by Myrica oil, and ants are also repelled by it (Skene et al. 2000).

Bog-myrtle is a species of wet heaths and blanket bogs whenever the peat is shallow (50-80 cm), but it also occurs in swamps and fens and can spread into adjacent marshy ground, even when there is some shade from willows and birch. The species is very much associated with oceanic climates where rainfall is both plentiful and regular, typically occurring around 200 days per year. It grows best in wet, but well-aerated soil, conditions often associated with water movement on slopes. Roots bear annual nitrogen-fixing nodules and plants can tolerate acidic conditions as low as pH 3.8. Near the sea, shrubs can spread from acid peat to colonise adjacent soils, thus displaying some degree of salt tolerance (Skene et al. 2000).

Fermanagh occurrence

As the tetrad distribution map shows, in Fermanagh M. gale is scarce and widely scattered in the lowlands, but it is very frequent over the whole of the upland Western Plateau boglands and taken together it occurs in 196 tetrads, 37.1% of those in the vice-county. It most typically grows in lakeshore swamps, fens, bogs and wet heathy moorland, but it does not survive on very exposed high ground, such as for instance the summit ridge of Cuilcagh.

Vegetative reproduction

M. gale reproduces vegetatively by suckers to produce thickets which dominate the ground they occupy. The suckers are often referred to as rhizomes, since although they become woody with age, they act as important over-wintering food stores maintaining the plant.

Flowering

The flowering strategy of M. gale is mainly dioecious (ie separate sexed bushes), but within a population monoecious bushes and bisexual flowers may also occur, so the species is really 'subdioecious' (Lloyd 1981). In April, the small, ovoid red-brown buds and the distinctive and striking red catkins and flowers appear on the bare branches before the leaves open (Skene et al. 2000). The flowers are wind-pollinated, but the amount of seed set is unknown. Establishment from seed is described as rare (Skene et al. 2000). Further work is needed to measure seed production.

A remarkable feature is that individual plants which bear flowers of one sex during a particular season may change to the other sex in the following year (Hutchinson 1972). In N Wales, Lloyd (1981) found that predominantly male stems were about 20 times as frequent as predominantly or strictly female stems. The pattern of gender variation appears to be environmentally induced, but the cause or causes remains a mystery, as does the advantage to the species.

When M. gale produces seed, it is water dispersed. The transverse bracts associated with the fruit act as swim bladders prolonging flotation (Skene et al. 2000). Biologically, the fruit is a small, green, resinous, 2-winged drupe-like nut containing one smooth, ovoid seed. It is fleshy outside, stony inside and secretes a considerable quantity of wax (Melderis & Bangerter 1955; Butcher 1961). The greasy wax covering of the fruit provides an aromatic tallow from which 'Bayberry' (an alternative common name) candles are made, the fruiting catkins being boiled in water to produce a scum beeswax (Grieve 1931; Stearn 1972).

Grazing pressure: M. gale is grazed by sheep, goats and hares, and shrubs may be reduced in height to 50 cm or less by such pressure (Skene et al. 2000). Interestingly, the Fermanagh farmer who owns the Carrickbrawn Erica vagans site near Belcoo, believes that sheep do not browse Bog-myrtle as hard as cattle do. The increased plant competition between M. gale and Erica species following removal of cattle from that site may help explain the observed contraction of the Cornish Heath population (see that species account).

British distribution: Bog-myrtle is very decidedly a plant of the N and W of Britain and Ireland, although it does also occur less frequently and intermittently in the S and E (Skene et al. 2001; New Atlas). Scotland is the principal area of distribution in Great Britain, and the BSBI Local Change Survey, a repeat sampling of the Monitoring Scheme survey carried out during 2003-4 showed a 2% mapped decline of recorded M. gale. This gave a Relative Change index of 10% overall. The editors of the report (Braithwaite et al. 2006), considered this a modest loss at the fringe of the distribution, readily explained by changes in land use associated with drainage and afforestation. In a few scattered sites in England, M. gale is recorded as an introduction (New Atlas).

European occurrence

In Europe, M. gale has a decidedly Atlantic and north-western distribution, co-incident with the lowland heathland region of Gimingham (1972). However, the distribution extends further north than this, stretching up the Atlantic coast of Norway and all around the shores of the Baltic Sea (Skene et al. 2000).

World occurrence

Beyond Europe, M. gale s.s. is widespread in N America, making it an amphi-Atlantic species. It is said to inhabit riverbanks and freshwater ponds in temperate parts of N America, a rather different habitat compared to that which it usually frequents in W Europe. A variety, M. gale var. tomentosa, is also widespread in E. Asia and NW America (Hultén & Fries 1986, Map 618).

Uses

In addition to the wax candles mentioned above, the use of M. gale as an insect repellent has been part of folklore for centuries (Grieve 1931). Midges are paralysed by Myrica oil, and ants are also repelled (Skene et al. 2000). Dried Bog-myrtle leaves were used to perfume drawers where linen was stored and to repel moths. Most interestingly, branches were used to flavour beer before hops became available in the 9th century (Simpson et al. 1996; Skene et al. 2000). The bark can also be used to tan calfskin, or to dye wool yellow (Grieve 1931). While the leaves are fragrant, they taste bitter and astringent, yet in China they are used to make tea, and used medicinally as a stomachic and cordial (Grieve 1931). A review of the uses of M. gale has recently been published by Simpson et al. (1996), in which it is suggested as a treatment for Herpes zoster.

Names

The name 'Myrica' is derived either from the Greek 'myron', meaning 'perfume' (Skene et al. 2000), or from the Greek 'myrike', the Classical name for Tamarisk (Stearn 1992). The specific epithet 'gale' is probably derived from Anglo-Saxon, Old English or German, 'gagel' or 'gagol', a vernacular name for Bog-myrtle, adopted as the specific name by Linnaeus (Grigson 1974; Stearn 1992). Additional common names include 'Sweet Gale', 'Flea-wood', 'Candle Berries', 'Bayberry', 'Wax Myrtle' and 'Golden Withy', the latter word referring to the flexibility of stems (Grigson 1987; Stearn 1992).

Threats

None.