The Whole and the Parts: Relationships Between Floral Architecture and Floral Organ Shape, and Their Repercussions on the Interpretation of Fragmentary Floral Fossils¹

Abstract

Floral architecture and floral organ shape are interrelated to some extent as can be seen in the diversity of extant angiosperm groups. The shape of fragmentary fossil material, such as single organs, may therefore give hints for the reconstruction of the architecture of a flower. This study is partly a review and partly provides original material and new points of view on organ-architecture interrelationships. Several topics are illustrated with examples: (1) autonomous and imprinted shape, exemplified by cuneate organs, especially stamens; (2) conditions for valvate anther dehiscence; (3) lability in number and shape of reduced organs that have decreased in size and lost their original function; (4) long hairs as filling material of irregular spaces; (5) architectural conditions for the presence of orthotropous ovules; (6) structural differences between exposed and covered organ parts in bud; and (7) sepal aestivation and petal elaboration.

Comparative floral structure and development of Nitrariaceae (Sapindales) and systematic implications

“…Th us, because of the phylogenetic position of Tetradiclis , the idea cannot be ruled out that the fl owers of Peganum are derived from isomerous, fully pentamerous ancestral forms. It is more likely, however, that the pentagonal shape of the gynoecium is superimposed by the pentamerous androecium as in analogous cases of other families discussed by Endress ( 2006Endress ( , 2008.…”

Ancestral traits and specializations in the flowers of the basal grade of living angiosperms

“…Subtending floral bracts are lacking, but the tightly arranged stamens (unistaminate flowers) are cuneate and in some species protect each other in bud with extended apices ( Fig. 11B; Endress, 2008b). It is possible that the floral subtending bract has not completely disappeared but is amalgamated with the stamen as the projecting apex.…”

“…They show a high degree of imprinted shapes (see Endress, 2008b). No other member of the ANITA grade is known to have this feature.…”

Changing views of flower evolution and new questions

“…Concomitant with this reduction, if the sepals are not completely lost, is an increase in number of the small sepals. In some moth-pollinated species with extremely elongate corolla, the reduced sepals are secondarily elongated as well, however, without re-gaining the lost protective function, and this secondary elongation seems to be merely a passive by-product of the elongation of the corolla (Endress, 2008b ). Phylogenetic analysis shows that such secondary elongation evolved more than once (Borg et al, 2008 ).…”