The evolutionary history and diversity of the Mickey Mouse Plants (the genus Ochna)

Abstract

Ochna is a palaeotropical genus with ca. 80 species distributed across continental Africa, Madagascar and the Mascarene Islands, and six species found in Asia. The genus holds ecological and cultural significance with many species being the dominant woody vegetation in parts of their range. Despite this importance, Ochna species are extremely under-studied and require detailed taxonomic attention to fully understand their evolutionary history. With the advances of high throughput DNA sequencing, the use of more robust molecular data combined with morphological data can be used to resolve species relationships in taxonomically challenging groups. A comparison of two target enrichment probe kits is conducted to determine the most efficient and suitable molecular methodology for producing a robust phylogenetic framework for Ochna species. A family-specific probe kit for Ochnaceae is showed to be the most efficient. The Ochnaceae-specific probe kit is then used to produce an updated infrageneric classification with 85% of accepted taxa. The results revealed three sections consistent with the current morphological classification and a new section from Madagascar and the Mascarene Islands supported by morphological characters. This phylogeny is then used to infer the ancestral history of the genus by investigating trait evolution and its biogeographic history. Employing ancestral state and range reconstruction revealed a shift in anther dehiscence correlated with shifts in other morphological traits and a successful speciation within the savanna biome. The phylogenetic framework elucidated various parts of the genus requiring taxonomic attention due to apparent paraphyly, including the ecologically important Ochna holstii. Finally, a detailed taxonomic revision is conducted using both molecular and morphological data to determine the species limits of O. holstii and closely related species. The study provides valuable insight into cryptic species and contributes towards more robust conservation assessments. The study is the first step towards a global monograph for the genus.