Were the five rare heathers of the west of Ireland introduced through human activity? An ecological, genetic, biogeographical and historical assessment

Abstract

Five rare Irish heather species have different disjunct ‘Lusitanian’ type distributions in Europe. They are confined in Ireland to the western coastal region and found elsewhere only, or principally, in the Iberian Peninsula. Two also occur in Britain, but only in the extreme southwest. None could have survived the last ice age in Ireland, and migration northwards, leaving hundreds of kilometre gaps en route, appears impossible. We assemble here the growing evidence that Erica ciliaris L. (Dorset Heath), E. erigena R. Ross (Irish Heath), E. mackayana Bab. (Mackay’s Heath), E. vagans L. (Cornish Heath) and Daboecia cantabrica (Huds.) K. Koch (St Dabeoc’s Heath) have been introduced inadvertently through human activity, along with another heathland Lusitanian species Simethis mattiazzii (Kerry Lily), if over a long period. We suggest that the proximity to the coast of extensive heathland habitats in northern Spain and western Ireland along with the cutting of heathland for bedding and packing in Spain is a probable cause of their inadvertent carriage on a direct maritime trade route which dates from prehistorical times. By considering them together, we suggest that until a precise date for the earliest arrival in Ireland of each species is established, they should all now be considered as naturalised archaeophytes.