Character evolution in Anaxagorea (Annonaceae)

Anaxagorta is a critical genus for understanding morphological evolution in Annonaceae because it shares a variety of features with other Magnoliales that have been interpreted as primitive relative to other Annonaceae. We present a detailed discussion of morphological characters used in a combined morphological and molecular phylogenetic analysis of Anaxagorea, along with implications of the analysis for character evolution in the genus. In spite of a high level of homoplasy in stamen and leaf venation characters, their removal results in loss of resolution in the trees obtained. The distributions of characters on trees confirm assumptions that several distinctive similarities between Anaxagorea and other Magnoliales are primitive retentions (e.g., the presence of an arlaxial plate of xylem in the midrib, nonpeltate stamen connectives, inner staminodes, and several leaf architectural characters). However, lateral extensions of the "laminar" stamens, though possibly ancestral in Anaxagorca, are convergent with those in other Magnoliales. A number of morphological synapomorphies have been identified for a clade containing most Central American species and another comprising all Asian species (e.g., conical bud shape and reduced inner petals for the Central American clade, and arlaxial cuticular striations and capitate stigma shape for the Asian clade).