Differentiating wild and domesticated bananas using volcaniform phytolith morphology and dimensions: Evidence from Sri Lanka

Abstract

Identifying domesticated banana phytoliths from archaeological sites within the natural geographical range of the wild progenitors of domesticated bananas is very challenging. This is because of the considerable similarity between phytoliths of domesticated triploid and tetraploid banana plants and those of the diploid species Musa acuminata and M. balbisiana in the Eumusa section, from which the domesticated varieties ultimately derive. This paper presents evidence for separating phytoliths derived from diploid, triploid and tetraploid banana plants in the Sri Lankan context. 8649 volcaniform (cavate) phytoliths from domesticated (triploid/tetraploid) banana plants and 2592 volcaniform phytoliths from diploid cultiwild and wild banana plants underwent morphotypic analysis into Ball et al.’s eight classes and were measured for basal length and crater width. Although there is overlap, modern domesticated triploid/tetraploid and diploid banana plants in Sri Lanka can be discriminated on morphotypic variation and size-ranges of volcaniform phytoliths. In our sampling, triploid and tetraploid banana plants have higher percentages of V3 morphotypes and generally higher percentages of V4 and V6 morphotypes of volcaniform phytoliths relative to M. acuminata and M. balbisiana, while V2 and V7 morphotypes are restricted to triploid and tetraploid banana plants and are not present in M. acuminata and M. balbisiana. Further, V4 and V8 are found in M. balbisiana, but not in M. acuminata. In Sri Lanka, mean basal length and crater width of volcaniform phytoliths in triploid and tetraploid bananas are greater than in M. acuminata and M. balbisiana. The overlap of size-ranges between phytoliths of triploid/tetraploid and diploid banana taxa is problematical, but threshold values of basal length > 29.1 µm and crater width > 12.1 µm can be used to distinguish some of the larger volcaniform phytoliths from triploid and tetraploid banana plants from those from and M. balbisiana, which do not exceed these dimensions in Sri Lanka, while M. acuminata volcaniforms do not exceed basal length of 27.2 µm and crater width of 10.2 µm. The size distributions of M. balbisiana volcaniforms suggest that two populations of this species are present in Sri Lanka, conceivably with different histories.