Morphological Characterization of Metamorphosis in Stamens of Anemone barbulata Turcz. (Ranunculaceae)

Abstract

The morphological characteristics of metamorphosis in stamens of Anemone barbulata Turcz. were investigated using morphological and histological analyses. The results showed that stamens were transformed into either white sepaloid organs or more frequently green leaflike structures with successive variations. The extreme metamorphic stamen was represented as a three-lobed leaflike structure with a long stalk, highly consistent with the morphological characters of the normal leaves of the plant. It was hypothesized that the connective and two pollen sacs of the anther were transformed into the three lobes of the metamorphosed stamen, respectively. The depression and circinate stages were identified as the important and necessary processes in the transformation of stamens from axial to foliar organs, suggesting probably the alternative evolutionary process of the formation of anthers derived from foliar organs. The morphological traces of leaf, sepal, and carpel observed in the metamorphosed stamens suggested the homeotic transformations among these organs. The foliar stage in the ancestral stamens of angiosperms was reflected ontogenically in the metamorphosed stamens of A. barbulata. Our findings of a series of metamorphic stamens probably represent the morphological evidence to support the hypothesis that the flowers of angiosperms were derived from metamorphic leaves with the progressive development mode in the evolution of floral organs.