Mackay’s heath at Lough Nacung Upper, near Dunlewy, Co. Donegal. Very similar to crossleaved heather but has a stronger and bushier habit.
St. Dabeoc’s heath with its urn-shaped corolla.
3. ST DABEOC’S HEATH
Confined to but very numerous in some locations in west Galway and in south and west Mayo from near Cong and Partry to the Killary Harbour and Croagh Patrick, and at Corraun on Achill Island. It was first unwittingly discovered by Edward Lhwyd, the great Welsh naturalist and antiquarian, who found it growing in most of the mountains of Galway and Mayo during a visit, probably mid May 1700. At the time he did not know it was St Dabeoc’s heath, describing it as ‘…an elegant sort of Heath, bearing large Thyme-leaves, a spike of fair purple Flowers, like some Campanula, and various stalk…’. He brought his specimens back to London and presented several to his friends there, including the botanist Petiver who later identified and described it in 1703.78 It is a small undershrub with straggly branches, often growing up through heather or gorse. Its leaves are narrow, elliptical, shiny green on top and whitish underneath. The large purplish corolla is about three times the size of those of bell heather. It is absent in Britain but found in southwest France as far north as the River Loire, and especially in the Cantabrian mountains, in the Spanish peninsula and the Azores. In the Pyrenees it survives quite happily under a snow covering for five months each year, belying the notion that it is a tender Mediterranean plant.
4. IRISH HEATH
First found by Mackay in 1830 on Errisbeg, near Roundstone, Co. Galway, and later in other localities in west Co. Galway. In Co. Mayo it is present at the mouth of Killary Harbour, on Clare Island, at Bellacragher Bay (north of Mallaranny), northwards to the Mullet peninsula and eastwards to Lough Conn (west and eastern shores). It is absent from Britain. The single station northwest of Bordeaux in southwest France is probably extinct.75 It occurs in good quantity in Portugal and in northwest Spain. Unlike the other heaths in Ireland, it may start flowering in January with the blooms at their finest in April, producing one of most magnificent botanical sights in the country. This hairless shrub forms dense stands, sometimes as high as 3 m, both at sea level (Praeger once observed it adorned with seaweed thrown up during storms) and on the mountainside (up to at least 155 m) rising up from the head of Bellacragher Bay. The sight of it here in early spring is a truly remarkable botanical feast.79 On the Bellacragher Bay mountainside the heather tracks the snaking pathways of small streams and rivulets that provide the plant with extra nutrients and moisture. Irish heath is also found further south, in the remarkable area of lowland blanket bog between Roundstone and Clifden, Co. Galway, that was covered with woods in the aftermath of the last glaciation. Jessen showed from the analysis of pollen remains found in the muds that Irish heath was growing in those woods, as it does in northwest Spain today.77 How it successfully survived the transition from a protective woodland environment to the barren, bleak and windswept blanket bog habitats in the west of Ireland is a tribute to its adaptive capabilities. Unlike the two other rare heaths, Dorset heath and Mackay’s heath, it is fertile and reproduces by seed. It has been argued by Foss & Doyle that it could have been introduced to Ireland by man some 500 years ago, at a time when there were direct trade links between Ireland, Spain and Portugal. Irish heath is found growing close to many pilgrimage shrines and abbeys in Portugal, Spain and France and it is postulated that it could have been carried by pilgrims.80
5. CORNISH HEATH
Originally found by Major Dickie of Enniskillen, but first reported by Praeger in 1938.81 It was growing on an isolated blanket bog near Belcoo, Co. Fermanagh, with white flowers (normally lilac-pink), and Praeger sided with those who considered the plant indigenous in a native habitat. Webb visited the bog in 1954 and reckoned that ‘the force of arguments were in favour of regarding it as native’.82 The site, close to a mineral flush, was visited in 1965 and 1966 by McClintock when about 1,000 plants were recorded.83 Another historical site was reported by Robert Burkitt in the 1850s, on the cliffs of Islandikane townland, west of Tramore, Co. Waterford, but the species has not been seen there since, despite repeated searches. It was naturalised on the sand hills at Dundrum, Co. Down, where it was discovered by Swanston in 1899, and was still present in 1978.84 It also grows on the rocky shore at Shane’s Castle, Co. Antrim. Outside Ireland it occurs in heaths in south Cornwall, and elsewhere in western Europe. It is a short to medium hairless undershrub with flowers ranging from white to pink to lilac. No evidence has yet been produced to show that Irish heath was a member of the Irish interglacial flora. Their seeds are consistently larger (c.0.7 mm) compared with c. 0.5 mm of other Erica species, so it would have been difficult to overlook them in samples of interglacial deposits.85
Irish heath with western gorse at Ballacragher Bay, Co. Mayo.
The Connemara and Burren plant assemblages
The congregation of the above ericaceous species in western Connemara is one example of apparent geographical plant madness, but the eclectic agglomeration of rare flowers in the Burren, Co. Clare, with representatives of arctic, alpine and Mediterranean floras also begs explanations. What could be the origin of such an unlikely association?
One interpretation postulates that these species originally had a more widespread range in Ireland. Although the Pleistocene glaciers probably wiped much of the landscape clean of living resources, some plants may have been able to avoid the ice blanket by moving up to the highest mountain peaks or sheltering in other refugia. Others, however, possibly shifted westwards to ice-free offshore islands and peninsulas. The sea level started to drop around 35,000 years ago, reaching its maximum fall of some 130 m below present day levels around 15,000 years ago. The west Clare and Connemara coastlines could then have extended perhaps some 45 and 10 km respectively west of today’s shorelines.2 Admiralty charts show commodious areas off the Burren coast stretching beyond the Aran Islands which would have been uncovered and well above water during the Ice Age. Assuming that the North Atlantic Current exercised some warming influence, the glaciers could not have impacted those areas. It is therefore possible that the plants may have survived in isolation on mist-shrouded, ice-free banks. As the glaciers withdrew and the sea started to rise again, the plants would have had to move back to the mainland. Despite the vegetative reproduction of most alpine species and presumed slow migration rates, the long time spans associated with the waxing and waning of the glaciers would have been sufficient to permit the relatively short migrations from the Burren and Connemara to those western tips and back again. Survival of plants during the first glacial epochs of the Ice Age on the summits of the Burren hills can probably be ruled out as all of them are too low to have escaped a scouring of the ice sheets (the highest is Slieve Elva at 344 m). However, several Burren hills were glacier-free during the last Midlandian glacial phase, towards the end of the Ice Age.
An alternative hypothesis regarding the survival of plants put forward by Mitchell & Ryan envisages a general migration of the various Burren and Connemara curiosities as well as other Lusitanian plant species up and down the western Atlantic seaboard from the Irish west coast to the shores of Spain and