Inflorescence and floral morphology of H aptanthus hazlettii ( B uxaceae, B uxales)

The enigmatic C entral A merican tree H aptanthus hazlettii has recently been placed in B uxaceae ( B uxales) by molecular evidence. However, H aptanthus appears morphologically to be fundamentally different from other B uxales in having pluriovular carpels with parietal placentation and reduced male reproductive units of an obscure morphological nature. The latter have been interpreted to be pairs of unistaminate flowers, or single flowers, either bearing two stamens or a pair of phyllomes with adnate introrse anthers. We (re‐)investigated the structure of the inflorescences and flowers of H aptanthus in order to clarify their homologies with reproductive structures of B uxales. We found that, despite some distinctive traits of flower morphology, H aptanthus shares many floral characters, including the opposite and pairwise arrangement of floral organs and the fusion between perianth members and stamens, with some B uxales and other early‐branching eudicots. The plicate and pluriovular gynoecium of H aptanthus may be the result of a drastic elongation of the symplicate zone, accompanied by an increase in ovule number, and is thus a derived trait in B uxales. The anther‐bearing structures are phyllomes with adnate anthers rather than stamens or unistaminate flowers. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 179 , 190–200.