Phylogenetic systematics of Cochlospermaceae (Malvales) based on molecular and morphological evidence

Cochlospermaceae (Malvales) is a small family of two genera, Amoreuxia and Cochlospermum. Cochlospermum has a pantropical distribution with species present in Mexico, Central and South America, the West Indies, Africa, India, Southeast Asia, and northern Australia, whereas Amoreuxia has a more restricted distribution in the Americas. Amoreuxia is comprised of four herbaceous species, and Cochlospermum has seven tree species and five that are suffrutescent subshrubs. The two genera also differ in floral symmetry, corolla coloration patterns, and stamen morphology. The goals of this study were to reconstruct the phylogeny of Cochlospermaceae to evaluate the monophyly of the family and its two genera, to resolve interspecific relationships, and to interpret patterns of morphological evolution. In addition, a minor goal was to examine its relationship to sister families, such as Bixaceae, a family in which Cochlospermaceae has been variously placed. Phylogenetic analyses were carried out using DNA sequences of the following markers: nuclear ribosomal ITS and the chloroplast trnG and trnL-F regions. The data support the monophyly of Cochlospermaceae and its distinctiveness from its sister families. While Amoreuxia is supported as monophyletic, Cochlospermum is paraphyletic with two species (C. orinocense and C. tetraporum) consistently placed outside a clade of all remaining Cochlospermum species. Ancestral character state reconstructions of morphology indicate that the tree habit may be ancestral in Cochlospermaceae with a single shift to an herbaceous growth form in Amoreuxia with the suffrutescent growth form having arisen twice within Cochlospermum, once in South America and once in Africa. There has been a single shift in floral morphology from radial symmetry, solid yellow petals, and uniform stamens to bilateral symmetry, two-toned petals, and dimorphic stamens in Amoreuxia. Anthers with one apical pore found in core Cochlospermum species may be a reduction from anthers with two pores, such as those found in Amoreuxia and in C. orinocense and C. tetraporum. Seed shape supports the sister relationships within Cochlospermaceae, particularly within Amoreuxia.