STRUCTURE OF BICARPELLATE GYNOECIUM IN <i>SYMPHYTUM</i> <i>ASPERUM</i> (BORAGINACEAE) IN RELATION TO EREM FORMATION

Abstract

The genesis of the bicarpellate syncarpous gynoecium was analysed in Symphytum asperum in relation to the septa formation in it, which determines the structure of erems (a dispersal unit of schizogenetic fruits forming as a result of dividing each carpel of syncarpous gynoecium into two independent parts) and the coenobium as a whole. In the gynoecium, at early stages of development, a short fertile synascidiate zone arises due to the formation of a basal septum (septum of 1st type) at the fusing of the involute carpel edges. A symplicate zone is formed above. A double U-shaped synplacenta appears at the gynoecium base. The structure of the basal septum is characterized by some features. The sutures that form the septum are obsagittate, with their wide part directed towards the center, and their narrow part directed outward. The septum of the 1st type is characterized by a 4-rayed structure, resembling an elongated rhombus or 2 tetrahedral pyramids facing each other: short rays are located between the walls of emerging erems of the same carpel, and long rays are between the walls of the erems of adjacent carpels. The central part of the septum subsequently stops developing, and the rays are transformed into branches of syncarpous sutures (2 in each carpel), to form 4 septa of the 2nd type. The length of the septa of the 2nd type increases longitudinally. In the wall of the ovary on the dorsal side in the area of the vascular bundle, 4 strands of small thin-walled cells are formed. Then, a splitting of these strands and the dorsal vascular bundle in half takes place. The septa of the 2nd type, like curtains or inserts, connect open ventral margins with dorsal halves of the ovary wall in each carpel, later becoming part of the pericarp of single-celled erems. At the same time, the symplicate zone is divided into 4 independent compartments. In S. asperum, septa of the 2nd type do not divide the loculi of carpels into 2 compartments and are not united into single partitions. They remain autonomous, growing between open edges of the halves in each carpel. The resulting diaspores (erems) are surrounded by a fruit coat on all sides. The outgrowths are not detected between the erems. This growth of the septa of the 2nd type is unique and correlates with the growth of the gynobasic style, while the shape of the growing septa ideally coincides with the shape of its faces.