Origin of the Angiosperm Flower

Abstract

Morphological and molecular analyses agree that angiosperms are monophyletic and somehow related to Gnetales, but uncertainties on rooting (among woody magnoliids or paleoherbs) and the position of fossils permit varied scenarios for origin of the flower. Trees linking angiosperms with Bennettitales, Pentoxylon, and Gnetales and this ''anthophyte'' clade with Caytonia imply that flowers arose in the common ancestor of anthophytes and carpels are cupule-bearing sporophylls. However, trees linking angiosperms with Caytonia and/or glossopterids imply that flowers originated more than once, as may certain fossil anthophytes. Trees linking anthophytes with coniferopsids suggest that flowers evolved by aggregation of fertile shoots into pseudanthia. New data on fossils or the control of floral morphogenesis in angiosperms and Gnetales might distinguish among these hypotheses.