Identification of late Holocene kōwhai (<i>Sophora</i>, Leguminosae) seeds from Central Otago dry rock shelters using nuclear DNA markers

Central Otago is one of the driest regions of New Zealand, with much of the natural vegetation lost to fires dating from the thirteenth century AD and agricultural land clearance in the nineteenth and twentieth centuries. Plant macrofossil records provide insights into the prehuman vegetation communities. Kōwhai (<i>Sophora</i> spp.) has been recognised as an important historical component of the natural vegetation of the Kawarau, Cromwell and Roxburgh Gorges of Central Otago. However, plant macrofossils are usually incomplete and this has created some uncertainty in identification of the <i>Sophora</i> species present. In different studies, leaflet and seed macrofossils have been identified as <i>S. microphylla</i>, <i>S. prostrata</i> and indeterminate <i>Sophora</i> species. <i>Sophora prostrata</i> has been recognised from Gibraltar Rock (Cromwell Gorge) based on macrofossil seeds having a brown-black testa, not the yellow testa characteristic of <i>S. microphylla</i> seeds. Late Holocene kōwhai seeds from other Central Otago locations are also brown-black. We extracted and sequenced nuclear DNA from four brown-black macrofossil <i>Sophora</i> seeds collected from Cairnmuir Gully rock shelter B (Cromwell Gorge) and Devils Creek rock shelter (Lake Dunstan), Central Otago. None of the seeds had SNP variants that are unique to <i>S. prostrata</i>, meaning they are most likely to be <i>S. microphylla</i>, the only other <i>Sophora</i> species that occurs in southern South Island and the only species persisting in Central Otago today. Furthermore, seeds of <i>S. prostrata</i> and <i>S. microphylla</i> have a different sized hilum. Seeds from Cairnmuir Gully rock shelter B, Devils Creek and Firewood Creek rock shelters have a hilum length consistent with <i>S. microphylla</i> and outside the range of <i>S. prostrata</i>. We conclude <i>S. microphylla</i> is historically and currently the only species of kōwhai in Central Otago and that the testa colour of its seeds can change from yellow to brown-black over long time periods.