The basal angiosperms are a grade comprising the main part of Magnoliidae sensu Cronquist (1981) minus Ranunculales, which belong to the basal eudicots. The monocots are nested within the basal Angiosperms. Figure 5.1 summarizes the phylogenetic relationships of the main families and orders according to Soltis et al. (2005). The position of Chloranthaceae and Ceratophyllaceae is debatable according to recent phylogenies, depending on emphasis on molecular or morphological analyses (see e.g. Moore et al., 1997; Jansen et al., 2007; Endress and Doyle, 2009).

The ANA-grade: Amborellales, Austrobaileyales, Nymphaeales

The ANA-grade (formerly ANITA-grade: Qui et al., 1999) groups the basalmost lineages of the Angiosperms. Among these taxa the monotypic Amborella trichopoda has recently been identified on molecular evidence as the basalmost extant angiosperm (Soltis et al., 2005; Jansen et al., 2007). Since then, morphological studies have confirmed the basal nature of these early-diverging lineages (see e.g. Endress, 2001; Ronse De Craene, Soltis and Soltis, 2003; Buzgo, Soltis and Soltis, 2004; Endress and Doyle, 2009). Most taxa of the ANA-grade share spiral (or whorled) flowers with a morphological continuum between bracts and perianth, indefinite number of organs and a central receptacular residue. However, perianth initiation and differentiation is variable in the grade. Endress (2008c) argued that a multistep gradation from bracts to inner tepals may be secondary, as this is absent from Amborella. Some characters appear derived and have evolved independently, such as unisexual flowers and adaptations to specific pollinators.