Systematic and evolutionary implications of stamen position in Myrteae (Myrtaceae)

The taxonomy of Myrteae, the most species-rich tribe of Myrtaceae, is notoriously difficult. Although the understanding of the phylogeny has improved, the morphological characteristics that support its cladistic configuration are still unknown. The present study evaluates stamen position and anthesis type as characters of systematic and evolutionary relevance. Sixty-nine species from 41 genera across the tribe were checked using herbarium material and spirit collections. The results recognize three patterns of stamen position in the pre-anthetic bud: straight, semi-curved and strongly incurved. The three patterns of stamen position correspond to the phylogenetic structure of the tribe, supporting the topology of the clades. Incurving of stamens across the evolutionary history of Myrteae appears to be linked to hypanthium extension and leads to different anthesis types that may be related to shifts in pollination strategy. The accessibility of stamen position and its systematic consistency make this character a useful tool for field and herbarium identification, and allow the inference of relationships for taxa not yet sampled in molecular analyses.