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Free Content A combined analysis of morphological traits, chloroplast and nuclear DNA sequences within Santiria trimera (Burseraceae) suggests several species following the Biological Species Concept

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Background and aims – Species delimitation remains a difficult task in many groups of organisms. Even widespread and conspicuous tropical trees make no exception. Santiria trimera, an African rainforest tree, displays substantial morphological variability. While classical analysis of historical herbarium samples lead to the recognition of a single species, two morphotypes of S. trimera are regularly collected in Gabon and Equatorial Guinea, sometimes in sympatry: one form with stilt roots (SR) and another form without stilt roots (NSR).

Methods – To assess whether these forms constitute distinct taxa and to understand evolutionary processes within African Santiria, we combined a morphological and a spatial analysis of both sympatric morphotypes in northern Gabon with a phylogenetic analysis of samples from West and Central Africa, including the island of São Tomé.

Key results – In Gabon, morphological traits, chloroplast DNA (cpDNA) and nuclear DNA (nuDNA) sequences congruently lead to the recognition of two well differentiated and reproductively isolated taxa corresponding to SR and NSR morphotypes. However, rare cases of the SR morphotype bearing DNA sequences typical of NSR individuals suggest that hybridization might sometimes occur. No evidence for habitat specialization of the two taxa was found. DNA sequences from São Tomé formed monophyletic clades at both marker types and the nuDNA gene tree suggests that the São Tomé population probably originated from Central Africa and subsequently underwent allopatric differentiation from continental populations.

Conclusion – In Central Africa, S. trimera is composed of at least two distinct sympatric species following the Biological Species Concept and calls for further morphological and phenological studies and experimental crosses between them to specify their taxonomic status. Our results also show that classical taxonomic species delimitation may not always be congruent with the Biological Species Concept, calling for more population-based in situ morphological and molecular genetic analyses.

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Document Type: Research Article

Publication date: 2010-07-01

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  • Plant Ecology and Evolution (a continuation of Belgian Journal of Botany, incorporating Systematics and Geography of Plants) is an international journal devoted to ecology, phylogenetics and systematics of all 'plant' groups in the traditional sense (including algae, cyanobacteria, fungi, myxomycetes), also covering related fields such as comparative and developmental morphology, conservation biology, ecophysiology, evolution, phytogeography, pollen and spores, population biology, and vegetation studies. It is published by the Royal Botanical Society of Belgium and the Botanic Garden Meise and contains original research papers, review articles, checklists, short communications and book reviews.

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