Sorbus hibernica E.F. Warb., Irish Whitebeam

Account Summary

Identification

S. hibernica is a shrub or small, deciduous tree up to 10 m tall with a broad, open crown and a trunk up to 30 cm in diameter. Leaves are un-lobed, elliptic to obovate and are clearly toothed along the whole of their margin except at the extreme base. The leaf teeth are straight, symmetrical and crowded in the upper half, acuminate, even and almost like a fine comb. The blade usually has 18-20 veins and the petiole is about 1.4 cm long. In Ireland, the leaves of S. hibernica most resemble those of S. aria (Common Whitebeam), although the leaves of the latter are slightly larger and their under-surfaces are densely white tomentose, rather than pale greyish-white with silky hairs beneath as in S. hibernica (Rich et al. 2010; Parnell & Curtis 2012).

Irish and British occurrence

The distribution in Ireland of S. hibernica is widely scattered, trees generally occurring in small numbers or as solitary individuals, in a wide variety of soils in both semi-natural and artificial habitat types, chiefly in Midland Ireland (Rich et al. 2005, 2010). Unlike many other species in the Subgenus Aria in Britain, S. hibernica occurs in a range of habitats on mountains and on lowland rocks and cliffs, rocky lake shores and islets, river gorges, open rock pastures and roadsides, hedges, open woods and copses (Rich et al. 2010).

Fermanagh occurrence

Since RHN first found specimens of this endemic apomictic Irish whitebeam on the shoreline and the scrub margins of plantation woodlands on the Castle Caldwell estate at the W end of Lower Lough Erne, he has since discovered it in a total of five Fermanagh tetrads, four of them around the same small area. The original discovery was made quite early on in Robert's recording career when he was naturally unsure as to exactly what he had found. Fortunately, he had the good sense to keep herbarium vouchers of unrecognised plants. During a fleeting visit to Fermanagh in August 2007, Dr Tim Rich, the BSBI Sorbus referee, confirmed the identification of the S. hibernica vouchers.

Spurred by the knowledge that this interesting, rare Whitebeam was indeed present in the county, in the autumn of 2007 RHN and HJN searched the scrub shoreline and sections of two peninsulas on the Castle Caldwell estate where the tree had first been encountered. Sixteen trees were discovered in two tetrads on Rossergole Peninsula, 14 specimens on the northern shore and two on the southern shore. A solitary tree was located near the eastern end of the adjacent larger Rossmore peninsula on the same estate. Both peninsulas were planted up with conifers sometime in the 1930s and the 17 specimens of S. hibernica are growing rather randomly scattered on the strip of shoreline that became exposed when the water level in Lower Lough Erne was lowered by drainage works in the 1870s. This strip was enlarged in the 1950s by further lake drainage. The latter adjustment was a desirable consequence of the development of the River Erne hydroelectric generation scheme, situated between Belleek, Co Fermanagh and Ballyshannon, Co Donegal and constructed between 1942-57.

The lake level reduction helped drain farmland around both parts of Lough Erne, ground which previously had been subject to unmanageable flooding despite the 19th century drainage efforts. The rocky limestone ground around the new shoreline has since been colonised by dense, almost impenetrable scrub, which made the task of surveying for S. hibernica extremely difficult. The survey is incomplete for this reason and perhaps dozens more trees might stand undetected, particularly on the long Rossmore peninsula where access is the most difficult. The trees discovered on the Castle Caldwell estate were 4-7 m in height and some were fruiting sparingly.

Certainly, the main area where this endemic species occurs is in the Irish Midlands, but the 17 individuals now known to occur at Castle Caldwell in Co Fermanagh make this the most important site for this endemic rarity in the whole northern province of Ulster.

Additional Irish Whitebeam specimens were subsequently discovered in Fermanagh at a second site lying on the S shore of Lower Lough Erne, 1 km E of Hill's Island in 2004. Three specimens were found at the end of a path from a small car park. They appear to have been deliberately planted in a line behind a wire fence. A fourth tree stands isolated further along the path. Apart from accompanying native willows, another definitely introduced tree at this site was Acer campestre (Field Maple). This secondary S. hibernica site is approximately 2 km south of the Rossmore peninsula, so the possibility of the specimens being of bird-sown origin should not be completely ruled out.

A third local station was discovered in 1989 lying about 6 km SSW of Enniskillen. Here, a solitary tree of S. hibernica is growing amongst birch on a cut-over bog at Gransagh, not far from the shore of Upper Lough Erne. Very probably this tree is another bird-sown individual.

It is very clear from this account that S. hibernica has been previously overlooked in Fermanagh, almost certainly because it has only recently been properly described (Warburg 1957), identification is not easy and relatively few Irish field workers can confidently recognise it from S. aria (Common Whitebeam). Thus, although there are many more plants and sites of this endemic recorded than previously was the case and there now are records from 31 of the 40 Irish VCs (the main exceptions being in the far SW), at the moment S. hibernica still remains under-recorded throughout Ireland (Rich et al. 2010).

• Find out more about the format of the species accounts
• View abbreviations
• View references for all species accounts
• View a gazetteer of all the sites