The Strawberry Tree (Arbutus unedo L.) is often referred to as one of Ireland’s ‘Lusitanian’ species to describe its disjunct distribution, since it is absent from Britain and is mainly found around the Mediterranean Sea and on the Iberian Peninsula. In Ireland, it is regarded as native in the south-west and in Co. Sligo. However, a recent genetic study suggests that it could have been introduced to Ireland directly from northern Spain. This possibility was previously dismissed, since palynological and archaeological evidence showed it to be present in south-west Ireland 4,000 years ago. Here, we examine how an introduction might have occurred prior to this date, by first reviewing what is known of its distribution, ecology and history in Ireland along with archaeological information. Then, combining an updated distribution of A. unedo where it is regarded as native in Ireland with historical accounts, palynological and archaeological records and other information from the literature, we present two online maps, designed to be an ongoing accessible resource. The information has enabled us to propose a means by which A. unedo might have arrived in Ireland with miners who came to work the first known copper mine in north-west Europe, in the Chalcolithic phase of the Late Neolithic, which was at Ross Island on Lough Leane in Co. Kerry. The species’ distribution today suggests that it then spread with subsequent Bronze Age copper mining activity in south-west Ireland, though this is unlikely to account for its arrival in Co. Sligo. Previous suggestions that A. unedo was once much more widely distributed in Ireland and subsequently contracted due to preferential cutting for smelting, are shown to be unfounded.

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.