Structure of the Bicarpellate Gynoecium of Symphytum asperum (Boraginaceae) in Relation to the Formation of Eremi

The genesis of the bicarpellate syncarpous gynoecium is traced in relation to the formation of septa in it that determine the structure of eremi and coenobium in general in Symphytum asperum. At early stages of development, a short fertile synascidiate zone arises in the gynoecium owing to a basal septum (first type septum) during the fusion of inverted carpel edges. A symplicate zone is formed above. A double U-shaped synplacenta emerges at the gynoecium basis. The basal septum structure is characterized by some peculiarities. The sutures that form it are obsagittate; at the same time, their wide part is directed to the center and the narrow part outward. The first type septum is characterized by a four-ray structure, resembling an extended rhombus or two tetrahedral pyramids facing each other: short rays are located between the walls of forming eremi of a single carpel, while long ones are between the walls of the eremi of adjacent carpels. Subsequently, the central part of the septum stops developing, and the rays are transformed into the branches of syncarpous sutures (two in each carpel), forming four second type septa. During the development, the length of these septa increases in a longitudinal direction. Four strands of small thin-walled cells are formed in the ovary wall from the dorsal side in the area of vascular bundle. Then there is a splitting of these strands and dorsal vascular bundle in half. In S. asperum, the second type septa are not combined into single partitions and do not divide the carpel locules into compartments. They remain autonomous and, like insertions, connect the open ventral edges with the dorsal halves of the ovary wall in each carpel. The obtained diaspores (eremi) are surrounded by the fruit membrane coat from all sides. Such a growth of the second type septa is unique and correlated with the growth of a gynobasic style; at the same time, the shape of the growing septa ideally coincides with the shape of its edges.