PATTERNS OF FLOWER AND INFLORESCENCE ARCHITECTURE IN CROCUS L. (IRIDACEAE)

In Crocus, inflorescence characters are widely used for intrageneric systematics. Despite of this, spatial relations of flowers and involucral leaves are poorly documented. The focus of our study was the paracladial region and spatha leaves of C. flavus and C. vernus. The first indication of the lateral position of the flower in both species was zygomorphy of the androecium and gynoecium. In other Iridaceae (Freesia, Gladiolus) stamens also have unequal length. The homeotic substitution of stamens by petaloid organs makes zygomorphy in Freesia more distinct, thus we propose that flowers have a latent genetic program for zygomorphization. The second indication is the bidentate shape of bracts and bracteoles in C. flavus and tridentate structure of the basal involucre in C. vernus, which we interpret as a fusion of the foliage leaf and the prophyll of the inflorescence. The shape and the position of the lateral inflorescences (paracladia) were also investigated. In C. flavus, corms often born several paracladia in the axils of the green leaves, whereas in C. vernus we found a single paracladium in the axil of a scale inside the basal involucre. The correlation between the number of paracladia, their position and the spathe leaves were discovered. We propose to use these characters for the definition of two subgenera in Crocus

PATTERNS OF FLOWER AND INFLORESCENCE ARCHITECTURE IN CROCUS L. (IRIDACEAE)

In Crocus, inflorescence characters are widely used for intrageneric systematics. Despite of this, spatial relations of flowers and involucral leaves are poorly documented. The focus of our study was the paracladial region and spatha leaves of C. flavus and C. vernus. The first indication of the lateral position of the flower in both species was zygomorphy of the androecium and gynoecium. In other Iridaceae (Freesia, Gladiolus) stamens also have unequal length. The homeotic substitution of stamens by petaloid organs makes zygomorphy in Freesia more distinct, thus we propose that flowers have a latent genetic program for zygomorphization. The second indication is the bidentate shape of bracts and bracteoles in C. flavus and tridentate structure of the basal involucre in C. vernus, which we interpret as a fusion of the foliage leaf and the prophyll of the inflorescence. The shape and the position of the lateral inflorescences (paracladia) were also investigated. In C. flavus, corms often born several paracladia in the axils of the green leaves, whereas in C. vernus we found a single paracladium in the axil of a scale inside the basal involucre. The correlation between the number of paracladia, their position and the spathe leaves were discovered. We propose to use these characters for the definition of two subgenera in Crocus

Flower Development

Flowers are the most complex structures of plants. Studies of Arabidopsis thaliana, which has typical eudicot flowers, have been fundamental in advancing the structural and molecular understanding of flower development. The main processes and stages of Arabidopsis flower development are summarized to provide a framework in which to interpret the detailed molecular genetic studies of genes assigned functions during flower development and is extended to recent genomics studies uncovering the key regulatory modules involved. Computational models have been used to study the concerted action and dynamics of the gene regulatory module that underlies patterning of the Arabidopsis inflorescence meristem and specification of the primordial cell types during early stages of flower development. This includes the gene combinations that specify sepal, petal, stamen and carpel identity, and genes that interact with them. As a dynamic gene regulatory network this module has been shown to converge to stable multigenic profiles that depend upon the overall network topology and are thus robust, which can explain the canalization of flower organ determination and the overall conservation of the basic flower plan among eudicots. Comparative and evolutionary approaches derived from Arabidopsis studies pave the way to studying the molecular basis of diverse floral morphologies