Folk taxonomical distinction between Irvingia gabonensis and I. wombolu (Irvingiaceae) in the Volta Forest region, West Africa

Abstract

Description of the subject. Irvingia gabonensis and I. wombolu produce edible kernels, with their fruit pulp tasting sweet and bitter, respectively. The overlap of their morphological and ecological traits creates taxonomic uncertainty. Objectives. This study assessed the efficiency of folk classification system for the separation between I. gabonensis and I. wombolu, in the Volta Forest region (Togo), where both species co-occur. Method. Interviews were conducted with 114 respondents of the five main sociolinguistic groups in the Volta Forest region, in order to identify distinctive traits between both species. Field reconnaissance and confirmation test were used to identify I. gabonensis and I. wombolu trees, which were evaluated against ecological features in folk classification system. Results. Variations existed within each species but were not botanically delimited. The folk classification system was mostly based on fruit pulp taste and some ecological traits. Old local residents only trusted fruit taste to separate these species. Only young Akposso men additionally considered ecology and leaf shape in classification. The reconnaissance survey confirmed the consistency of their folk classification system. Dendrometric parameters of I. gabonensis depended on environmental factors, while land use system and soil geomorphology significantly influenced the occurrence of I. wombolu. Conclusions. Fruit pulp taste and flowering seasons were widely used to distinguish between species, while young men used ecological and botanical features. This demonstrates their recent contact with these taxa. It is also likely that domestication is narrowing differences between I. gabonensis and I. wombolu.