THE SCENT OF INTRUDERS

Diarmuid Breatnach

The inhabitants of this land have fought invaders for at least a thousand years, some successfully and some less so. Many of the invaders were assimilated. Throughout this time, other invaders have quietly entered and spread throughout the land, mostly without encountering any organised opposition.

Last month and perhaps occasionally since, your nose might have picked up a scent drifting towards you, particularly as evening drew near but also at other times. The aroma I speak of is one of those scents that is difficult to describe and that actually seems to change from time to time and also according to whether one is right beside it or farther away. Sometimes it seems musky and very pleasant while at other times is not so welcome.

The scent may have been from the blossoms of the Cherry Laurel (Prunus laurocerus), a dense thicket-forming shrub that grows to small tree size with a strong thick trunk covered in a smooth dark grey bark. It is neither a cherry variant nor a laurel (or bay), which its leaves supposedly resemble, these being thick and dark green but poisonous (containing cyanide). The blossoms, white flowers clustered on upright spikes, produce blackish fruit in the Autumn about the size of cherries which are also poisonous to humans. Originally from South-West Asia, it was introduced into Irish gardens as a shrub or hedge plant (uses to which it is still put) but it has “escaped” and established itself in the wild.

Cherry Laurel bush with flowering spikes in early stage

The Cherry Laurel has become very successful and a resultant problem for bio-diversity in Ireland. A quick perusal of the on-line references do not reveal the reason for its success; it tends to be grouped alongside another invasive species, the Rhododendron, which deposits a chemical in the ground surrounding it, thereby preventing other plant species competing with it for light, moisture and nutrients. Like the Cherry Laurel, the Rhododendron is a plant species invasive to Ireland. Of course, since Ireland was almost entirely covered in ice 20,000 years ago, nearly all of the plant life now naturalised on our island had to have been invasive species originally — including trees, bushes, flowers, grasses, ferns …

Cherry Laurel flowering spikes at late stage

Invasive species are not always harmful to the existing balance (or to humans) but clearly they have to have some means of competing with the existing flora (plant life) or they would have been unable to establish themselves. They may have better protection against herbivorous animals (undoubtedly the Cherry Laurel has at least that), or against insect or snail attack, or even against fungi (such as the ‘blight’ that attacked the potato a number of times in Ireland in the 1840s). Or they may be able to occupy a niche not well exploited so far, as one of the Buddleida species has done (literally, one might say), growing out of thin gaps in stone or brick walls or on waste ground, its racemes of mauve or purple flowers attracting butterflies and other insects for pollination and later scattering its seeds on the wind.

The Luftwaffe helped the spread of the plant in Britain; so common did this shrub become on waste ground after the Second World War that it earned the popular name of « Bombsite Plant ». The species in question is Buddleia Davidii and according to The Online Atlas of British and Irish Flora, it was introduced into cultivation in the 1890s, quickly becoming very popular in gardens. By 1922 it was known to be naturalised in the wild in Merioneth and in Middlesex by 1927; it is shown as locally well established in S. England in the 1962 Atlas and “In recent decades it has spread rapidly throughout lowland Britain and, to a lesser extent, Ireland.” It is certainly ubiquitous in Dublin city and surrounds.

Buddleja Bush in bloom — Buddleia Bush in bloom

Buddleja davidii growing out of a wall — Buddleia davidii growing out of a wall

Buddleia (pronounced “budd-lee-ah) has about 100 species native to all continents except Europe and Australasia but a number of species and cross-breds are cultivated in European gardens, including the escapologist davidii. Although nearly all are shrubs growing to at most 5m (16ft) tall, a few species qualify as trees, the largest reaching 30m (98ft). There are both evergreen and deciduous species, not that unusual among trees and shrubs, as appropriate in tropical and temperate regions respectively. Some of the South American species have evolved long red flowers to attract hummingbirds, rather than insects, as exclusive pollinators.

Peacock Butterfly on a Buddleja raceme — Peacock Butterfly on a Buddleia raceme

In Ireland, far from hummingbirds, davidii’s racemes of tiny purple or mauve flowers are a welcome sight as they flower in July, less so as the flowers, having done their work, die and turn brown (though repeated dead-heading can extend flowering until September). The flowers are scented but less so than those of the similar but not closely-related Common Lilac (Syringa vulgaris) which, incidentally, is an aggressive coloniser in parts of Southern Europe and of the USA. The roots of davidii will do some damage to house walls and chimney stacks if allowed to become established, when pulling them out becomes impossible and the stump would need treating with an appropriate chemical. Checked early, it is easily controllable.

Another successful wall climber in Ireland is the Red Valerian (Centranthus ruber), sometimes known as Jupiter’s Beard. Despite its common name, the flowers are often pink or even white and at times clumps of two or even all three colours may be seen growing alongside one another. This one likes the tops of walls rather than the sides and grows well on dry or stony soil too.

Its seeds are wind-driven too and from anecdotal evidence, it made particular use of the railway cuttings and lines to distribute itself throughout Ireland.

Despite its name, it is not closely related to the true Valerian (Valeriana officinalis), and no medicinal properties have been discovered in Centranthus. The leaves and the root may be eaten but there seems to be no great lobby recommending it as food. Its scent is rather rank to the human nose.

The three colour variations of Ceranthus Ruber growing closely together on rocky ground

Originally from S.W. Europe and the Mediterranean region, the plant was grown in Britain as early as 1597, according to Online Atlas of British & Irish Flora. Like some cases in human history, when the newcomers were first invited and then became invaders, Red Valerian was first imported to be grown in gardens. By 1763 it was recorded in the wild in Cambridgeshire. Now it is to be found all over Ireland and is generally welcomed. Like some of the invading Vikings, Normans and English, Red Valerian and Buddleja have become part of the Ireland we know today and there seems no need to organise a resistance to them; the Cherry Laurel and the Rhododendron, despite the scent of one and the colour of the other, are a different case altogether.