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Free Content Straddling the Mozambique Channel: molecular evidence for two major clades of Afro-Malagasy Schefflera (Araliaceae) co-occurring in Africa and Madagascar

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Background and introduction Schefflera is the largest genus in Araliaceae, with approximately 900 species. However, recent studies have shown that Schefflera is polyphyletic, representing no fewer than five distinct clades, each corresponding to a specific geographic region: Asia, continental Africa plus Madagascar, Melanesia, the Neotropics, and a small clade in several archipelagos of the Pacific Ocean. The Afro-Malagasy clade comprises 49 species distributed throughout tropical Africa, Madagascar, the Comoro Islands, and the Seychelles. Previous studies have suggested that this group is monophyletic, identifying two subclades (which largely correspond to informal morphogroups identified as 'Meiopanax' and 'Sciodaphyllum').

Methods – Using sequence data from nuclear rDNA and chloroplast spacers derived from 33 of the 49 currently circumscribed species of Afro-Malagasy Schefflera, this study tested the group's monophyly and that of its two informal subgroups. We utilized alternative partitioning schemes to explore the combinability of datasets from the distinct genomic regions sampled.

Key results – Our results support the monophyly of Afro-Malagasy Schefflera and its two informal subgroups, 'Meiopanax' and 'Sciodaphyllum'. Each of these subgroups include species from both continental Africa and Madagascar, although species diversity in 'Meiopanax' is heavily based in Madagascar. In 'Sciodaphyllum', species diversity is much greater in continental Africa, despite evidence for more widespread dispersal events that have led to subsequent speciation in both Madagascar and the Seychelles Islands. Among several species that appear to be non-monophyletic, S. myriantha stands out as particularly problematic. This species, which shows very little morphological variation across its wide distribution in Africa and Madagascar, forms two subclades, one restricted to Africa, and another from Madagascar that also includes two additional, morphologically distinctive species.

Conclusions – This study makes an important contribution towards the circumscription of one of the five clades currently treated as Schefflera s. lat. and is the most inclusive systematic study of Afro-Malagasy Schefflera to date. Our results support the monophyly of both informal groups 'Meiopanax' and 'Sciodaphyllum', which we propose to recognize as two separate genera, Neocussonia and Astropanax, respectively.

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Document Type: Regular Paper

Publication date: April 1, 2017

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