Correlations between gynoecium morphology and ovary position in angiosperm flowers: Roles of developmental and terminological constraints

Abstract

The angiosperm gynoecium consists of elementary units called carpels. These can be free (apocarpy) or united (coenocarpy, or syncarpy in a wide sense). One of the most complicated problems of evolutionary morphology of angiosperms is distinguishing monomerous and pseudomonomerous gynoecia. The former are assumed to be derived by the reduction of the carpel number in apocarpous gynoecia, and the latter are assumed to be derived by reduction of gynoecia with united carpels. Pseudomonomerous gynoecia have one fertile carpel and more or less prominent traces of sterile carpel(s). In extreme cases of reduction, pseudomonomerous gynoecia are very similar to monomerous, even though the two types have completely different evolutionary histories. G.B. Kedrov (1969) proposed a new approach to resolve the issue. Using the absence of polymerous free-carpellate gynoecia with inferior ovaries, he suggested that there is a constraint for epigyny in plants with free carpels. Therefore, in taxa with disputable morphological interpretations, the gynoecium should be treated as pseudomonomerous (and not monomerous) if the ovary is inferior. A critical review of the concept of G.B. Kedrov showed that his ideas would suggest reinterpretation of widely accepted views on gynoecium morphology in several key families of basal angiosperms. An alternative view is proposed: for the most important types of epigyny in angiosperms, the “constraint” for the combination of inferior ovary and apocarpy is due to the definition of the term “apocarpy” only. There is no biological sense in this “constraint.” The existence of two other morphogenetic constraints is proposed: (1) on the presence of a typical inferior ovary in monomerous gynoecia with conduplicate carpel and (2) on the radial (sectorial) fusion of individual carpels with stamens or perianth members without fusion of these groups into an entire structure. The possible biological nature of these constraints is discussed.