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Molecular phylogenetics and morphological evolution of St. John's wort (Hypericum; Hypericaceae)
Nicolai M Nürk1, Santiago Madriñán, Mark A Carine
1Leibniz Institute of Plant Genetics and Crop Research, IPK, D-06466 Gatersleben, Germany. nuerk@ipk-gatersleben.de
Molecular Phylogenetics and Evolution
|October 13, 2012
Summary
This study reveals the evolutionary relationships within the Hypericum genus using DNA sequencing. It clarifies the placement of related genera and identifies key morphological traits driving diversification in St. John's wort.
Area of Science:
- Botany
- Evolutionary Biology
- Molecular Phylogenetics
Background:
- Previous phylogenetic hypotheses for Hypericum (St. John's wort) relied heavily on morphology, with limited molecular data.
- Existing molecular studies have sampled only a small fraction of the diverse Hypericum species.
Purpose of the Study:
- To construct a robust phylogenetic hypothesis for the large, cosmopolitan genus Hypericum.
- To investigate the evolutionary relationships among Hypericum, Triadenum, and Thornea within the Hypericaceae family.
- To reinterpret morphological evolution within Hypericum based on molecular data.
Main Methods:
- Phylogenetic analysis using 360 internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA (nrDNA).
- Inclusion of 206 species from Hypericum (including Triadenum and Thornea) and three other Hypericaceae genera.
- Application of parsimony and model-based phylogenetic inference methods.
- Bayesian reconstruction of ancestral states for morphological characters.
Main Results:
- The genus Triadenum is nested within Hypericum, specifically in a clade with New World species.
- Thornea is identified as the sister genus to Hypericum.
- Three major clades and two smaller grades were resolved within Hypericum, correlating with morphological characteristics.
- Approximately 60% of Hypericum sections were found to be monophyletic relative to the current classification.
- Shrubby habit is inferred as the ancestral state, with herbaceous forms evolving multiple times.
- Convergent evolution of arborescent species occurred in high-elevation tropical habitats of Africa and South America.
Conclusions:
- The study provides a comprehensive molecular phylogeny for Hypericum, refining its classification and evolutionary history.
- Morphological characters play a significant role in defining major clades and understanding evolutionary trends within the genus.
- The findings highlight multiple independent origins of herbaceous growth forms and convergent evolution of tree-like habits.
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