Integrating Early Cretaceous Fossils into the Phylogeny of Living Angiosperms: ANITA Lines and Relatives of Chloranthaceae

Premise of research. Discoveries of fossil flowers in Cretaceous rocks offer improved evidence for relationships with living clades, but for more secure inferences formal phylogenetic analyses are desirable. We extend previous analyses of magnoliids, monocots, and basal eudicots to Aptian, Albian, and Cenomanian fossils related to the basal ANITA lines and Chloranthaceae. Methodology. We performed parsimony analyses of a morphological data set of Recent angiosperms and published fossils, with the arrangement of Recent taxa constrained to backbone trees based primarily on molecular data. Pivotal results. Not only Monetianthus (as previously inferred) but also Carpestella is nested within Nymphaeaceae, while Pluricarpellatia may be a stem relative of Cabombaceae or Nymphaeaceae. Anacostia (with Similipollis pollen) is nested within Austrobaileyales. The position of Couperites (with Clavatipollenites pollen) is ambiguous: it may be on the stem lineage of Chloranthaceae (and Ceratophyllum, if this extant aquatic is related to Chloranthaceae), nested in Chloranthaceae, or more basal. Plants with Asteropollis pollen and reduced tepals are related to the chloranthaceous genus Hedyosmum. Zlatkocarpus, which also has a reduced perianth, may be either a stem relative or a crown group member of Chloranthaceae. Plants that produced loosely reticulate Pennipollis pollen are more likely related to Chloranthaceae and/or Ceratophyllum than to monocots. We confirm that Canrightia, with bisexual flowers and a reduced perianth, is a stem relative of Chloranthaceae. Despite similarities to Piperales, Appomattoxia (with Tucanopollis pollen) is more likely near the base of the ANITA grade or related to Chloranthaceae and/or Ceratophyllum. Conclusions. The Cretaceous rise of angiosperms involved the radiation not only of magnoliids, eudicots, and monocots but also of basal ANITA lines, including both aquatic Nymphaeales and woody groups. Our results reaffirm the early diversity of Chloranthaceae and clarify their floral evolution, in which a shift to unisexual flowers preceded loss of the perianth.