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27 December 2010 Flower Structure and Trends of Evolution in Eudicots and Their Major Subclades
Peter K. Endress
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Eudicots and their currently recognized major subclades are characterized as to floral structure (including some “embryological” features) based on ca. 3000 original publications. A new classification of nucelli is presented. In particular, the distinction between tenuinucellar and incompletely tenuinucellar ovules has proven to be useful for the characterization of larger subclades. Tenuinucellar ovules characterize Gentianales, and largely Lamiales of lamiids, and Asteraceae of campanulids, thus all of the most diversified subclades of asterids. In contrast, incompletely tenuinucellar ovules are present in basal asterids and the less diversified subclades of lamiids and campanulids. Interestingly, Santalales and Caryophyllales, which have been tentatively classified in the asterid lineage s.l., have relatively thin nucelli. Also, the presence of endosperm haustoria or the particular differentiation of the embryo suspensor characterizes some larger subclades such as Fabales and Lamiales or core Saxifragales, respectively. The expanded malvids (with inclusion of Crossosomatales, Geraniales, and Myrtales) are supported by floral features. For several features that are potential key innovations, because they characterize strongly diversified clades (e.g., pentamerous flowers in core eudicots or monosymmetric flowers in Lamiales), it is shown that they are also sporadically present in species-poor clades more to the base of the phylogenetic tree. This indicates that what appear as key innovations in certain groups may be present in latent form long before their manifestation as a key innovation. Thus, it is possible that such key innovations are not always apomorphies in a strict sense (e.g., monosymmetric flowers). This conforms with results of evo-devo research, in which genetic structures connected with floral features were found in clades in which the floral features are not present.

Peter K. Endress "Flower Structure and Trends of Evolution in Eudicots and Their Major Subclades," Annals of the Missouri Botanical Garden 97(4), 541-583, (27 December 2010).
Published: 27 December 2010

basal eudicots
core eudicots
evolutionary trends
floral diversity
floral structure
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