Strawberry Tree - Arbutus unedo
The Strawberry Tree (Arbutus unedo) has, unusually for a member of the Ericaceae, the habit of a tree. Also unusual is the fact that it bears flowers and fruit (from previous flowering) at the same time, the fruit taking a year to ripen. The fruit is not poisonous. The pale cream bell shaped (like other Ericaceae) flowers appear late in the year, September to October. Arbutus trees do not survive if overshadowed, so do not thrive in woodlands, and appear to prefer steep rocky slopes - but that might be where they suffer less damage from grazing, rubbing by animals, overshadowing by larger trees etc. They grow well in deep soil too, and prefer acidic soil conditions.
Like other members of the Ericaceae the pollen occurs as tetrads. As Oldfield (1) states, the differential identification of Ericaceae pollen is not easy. He gives some average sizing and characteristics in his paper. Tetrad lager diameter si between 51 and 60 microns; single grain diameter between 40 and 47 in the plane of attachment, and 39 to 43 otherwise. The tetrad is globular and each grain is sub-triangular, with fine and indistinct granulation as ornamentation. The flowers are entomophilous (pollinated by insects), so pollen production is relatively low and fossil pollen does not occur widely in organic sediment. The flowers are monoecious, bearing male and female parts within the same flower.
Arbutus unedo is a member of what has come to be known as the Lusitanian Flora, a group of plants that occur in south west and western Ireland, but are originally from and native to, The Western Iberian peninsula i.e Portugal. A recent paper (2) suggests a link between the Beaker folk copper prospectors and miners that came from Iberia around 2500 BC. There appears to be strong evidence of a co-occurence of Bronze Age copper mines, Beaker burials, and the Strawberry Tree. It is suggested that the miners broght the tree with them to ensure a supply of the fruit with which they possibly made an alcoholic 'wine'. Such liquor is made in Portugal today. The modern day distribution of this tree suggests it is not native, but Arbutus unedo is not marked as 'introduced' in Webb's Irish Flora.
References
1. Frank Oldfield. 1959. The Pollen Morphology of some of the West European Ericales - preliminary descriptions and a tentative key to their identification. Pollen et Spores. Vol 1. pp 19-48.
2. Micheline Sheehy Skeffington and Nick Scott. 2021. Is the Strawberry Tree, Arbutus unedo (Ericaceae), native to Ireland, or was it brought by the first copper miners? British & Irish Botany 3(4): 385-418.
