Was this shrub introduced from north of Spain?
MACKAY’S HEATH is an interesting wild plant. It is a heather-like, bushy shrub that displays masses of small, bright pink flowers in late summer. It is native to and is only found in four provinces in the coastal Cantabrian region of north-west Spain. The only other place in the world where it occurs is along the western seaboard of Ireland.
It grows at six sites, one in each of counties Kerry and Donegal and two in each of counties Galway and Mayo. Its distribution is very local and disjunctive in deep peat in the drier fringes of wet blanket bogs near the sea.
Even though its pollen is fertile, for some unknown reason, the plant does not set seed in Ireland. It spreads by layering and does so freely, possibly aided by turf cutting.
Mackay’s Heath is regarded as native to Ireland but how it got here is not understood. It is generally believed that the intense cold and the ice sheets of the last ice age wiped out all of the wild plants that grew here at that time.
If so, Mackay’s Heath must have colonised Ireland by spreading north from Spain when the ice melted and the climate improved some 13,000 years ago. But how could it get here?
It is believed that Ireland became an island about 7,500 years ago when meltwater from the ice caused sea level to rise cutting off our land links with Britain and mainland Europe.
Another possibility is that Mackay’s Heath survived the last ice age in Ireland. However, since it is essentially a Mediterranean plant, that seems unlikely when there is no evidence to suggest that much hardier species were able to survive being locked in the chilly embrace of the prolonged Arctic cold.
Intriguingly, research for a recent study by botanists from Galway university reported in the current issue of the New Journal of Botany notes that in Ireland Mackay’s Heath always grows within 1km of tracks and roads near sandy bays. Does that suggest that Spanish traders using these trackways might have introduced the species to Ireland from Cantabria, Galicia or Asturias?
It is known that heathers and heaths were used in the past as packing material around imported goods and genetic studies suggest that Irish specimens of Mackay’s Heath are more closely related to those in Spain that to other Irish plants suggesting repeated introductions.
The present status of Mackay’s Heath as a native Irish plant is coming under increasing doubt.
As they fade, the pink flowers of Mackay’s Heath turn bright orange.