Flower symmetry is of special interest in understanding angiosperm evolution and ecology. Evidence from the Antirrhineae (snapdragon and relatives) indicates that several TCP gene-family transcription factors, especially CYCLOIDEA (CYC) and DICHO-TOMA (DICH), play a role in specifying dorsal identity in the corolla and androecium of monosymmetric (bilateral) flowers. Studies of rosid and asterid angiosperms suggest that orthologous TCP genes may be important in dorsal identity, but there has been no broad phylogenetic context to determine copy number or orthology. Here, we compare published data from rosids and asterids with newly collected data from ranunculids, caryophyllids, Saxifragales, and Asterales to ascertain the phylogenetic placement of major duplications in the ''ECE'' (CYC͞TB1) clade of TCP transcription factors. Bayesian analyses indicate that there are three major copies of ''CYC'' in the ECE clade, and that duplications leading to these copies predate the core eudicots. CYC1 contains no subsequent duplications and may not be expressed in floral tissue. CYC3 exhibits similar patterns of duplication to CYC2 in several groups. Using RT-PCR, we show that, in flowers of Lonicera morrowii (Caprifoliaceae), DipsCYC2B is expressed in the four dorsal petals and not in the ventral petal. DipsCYC3B is expressed in flower and petal primordia, possibly most strongly in the ventral petal.CYCLOIDEA ͉ ECE clade ͉ floral symmetry ͉ gene duplication ͉ TCP

Scaevola, the only genus of Goodeniaceae that has extensively radiated outside of Australia, has dispersed throughout the Pacific Basin, with a few species reaching the tropical coastal areas of the Atlantic and Indian Oceans. Five Australian and most of the non-Australian species are placed in Scaevola section Scaevola based on their fleshy fruits, indeterminate inflorescences, and more arborescent habits. Analyses of ITS sequence data demonstrate that Scaevola is a monophyletic group if S. collaris is excluded and Diaspasis filifolia is included. The genus is Australian in origin, but there have been at least six separate dispersal events from Australia. Four of these dispersals each resulted in single extra-Australian species. The remaining two were followed by radiations that gave rise to large groups, each including one of the widespread strand species, S. taccada and S. plumieri. Remarkably, three of the six dispersals established species on the remote Hawaiian Archipelago, representing at present the largest number of colonizations by any flowering plant genus to these islands.

The transition to bilateral symmetry in Caprifoliaceae involved: (a) duplication of an ancestral DipsCYC2 gene; (b) the loss of expression of both of these copies in the ventral petal; and (c) changes in the zone of expression, with one copy continuing to be expressed across the dorsal and lateral petals, and the other copy becoming restricted in expression to the dorsal corolla lobes.

Flower symmetry is of special interest in understanding the evolution and ecology of angiosperms. Evidence from the Antirrhineae (within the lamiid clade of Asteridae) indicates that several TCP gene family transcription factors, especially CYCLOIDEA (CYC), play a role in specifying dorsal identity in the corolla and androecium of monosymmetric (bilateral) flowers. We examine the evolution of this gene family in Dipsacales, representing the campanulid clade of Asteridae, in relation to evolutionary shifts in floral symmetry and stamen abortion. We identify three major forms of CYC-like genes in Dipsacales. We identify the position of additional gene duplications by comparing each of the three gene trees to a well-supported Dipsacales phylogeny. We infer duplications in two of the major gene lineages along the line leading to the Caprifoliaceae correlated with the origin of monosymmetric flowers. There are no duplications or losses associated with major shifts in stamen number. However, there are several additional duplications within the Caprifoliaceae, especially in the Morinaceae, possibly related to calyx monosymmetry and/or stamen reduction. Within the protein-coding sequences, we identify a new conserved region-the ECE region-that appears to be present across known angiosperm sequences. There are major changes in length and in the presence or absence of the ECE region in the Dipsacales, indicating changes in gene function. These studies expand our understanding of the evolution of CYC-like genes in angiosperms and provide a new system for studying the role of this gene family in determining floral form.

The origin of the flower was a key innovation in the history of complex organisms, dramatically altering Earth’s biota. Advances in phylogenetics, developmental genetics, and genomics during the past 25 years have substantially advanced our understanding of the evolution of flowers, yet crucial aspects of floral evolution remain, such as the series of genetic and morphological changes that gave rise to the first flowers; the factors enabling the origin of the pentamerous eudicot flower, which characterizes ∼70% of all extant angiosperm species; and the role of gene and genome duplications in facilitating floral innovations. A key early concept was the ABC model of floral organ specification, developed by Elliott Meyerowitz and Enrico Coen and based on two model systems, Arabidopsis thaliana and Antirrhinum majus. Yet it is now clear that these model systems are highly derived species, whose molecular genetic-developmental organization must be very different from that of ancestral, as well as early, angiosperms. In this article, we will discuss how new research approaches are illuminating the early events in floral evolution and the prospects for further progress. In particular, advancing the next generation of research in floral evolution will require the development of one or more functional model systems from among the basal angiosperms and basal eudicots. More broadly, we urge the development of “model clades” for genomic and evolutionary-developmental analyses, instead of the primary use of single “model organisms.” We predict that new evolutionary models will soon emerge as genetic/genomic models, providing unprecedented new insights into floral evolution.