This book is not exhaustive, as the total number of families has not been covered, although it is comprehensive in reflecting floral diversity of the majority of angiosperms. Major groups of angiosperms have been covered to reflect important floral evolutionary patterns. Sections below summarize most important floral attributes of major clades of angiosperms.

Basal angiosperms, monocots and early diverging eudicots

Floral evolution of basal angiosperms has been studied in a phylogenetic context by several authors (e.g. Doyle and Endress, 2000; Ronse De Craene, Soltis and Soltis, 2003; Zanis et al., 2003; Endress and Doyle, 2009). Mapping of floral characters on phylogenetic trees implies that cyclic flowers have evolved rapidly from a helical flower with relatively few stamens and carpels as in Amborella and the ANA-grade (Austrobaileyales, Nymphaeales, Amborellales), with frequent reversals to a spiral phyllotaxis in different orders. The most recent addition in Nymphaeales, Hydatellaceae, raises questions about the flowers of the earliest angiosperms (see Rudall et al., 2007; Endress and Doyle, 2009).

Flowers of basal angiosperms have a low synorganization with high plasticity in organ number and position (Endress, 1990, 2001, 2008c). The transition between vegetative shoot and flower is often gradual with a progressive change from leaves to bracts and tepals within the inflorescence or at the base of the flower (Endress, 2003b; Remizowa and Sokoloff, 2003; Buzgo et al., 2007). Several taxa, also in early diverging eudicots and basal monocots, have an unclear distinction between bracts and perianth.