Morphological and anatomical investigation of seed conesof Cupressus glabra (Cupressaceae) : evolutionary aspects

Abstract

Within this study, the morphological and anatomical features of Cupressus glabra Sudw. seed cones were investigated, focused on the vascular supply to cone scales and ovules. These investigations should help towards a better understanding of the branching pattern both within seed cones of C. glabra and within in the primitive cupressaceous seed cones in general. Seed cones of C. glabra are strongly reduced and compact structures. They typically lack sterile distal elements, so that all terminal cone scales are usually fertile, and the apex of the cone axis is not visible. The ovules are arranged in up to four axillary rows. Each row, which can be understood as a descending accessory shoot, consists of several ovules. Within a bract/seed scale complex the cone scale and its axillary ovules are each supplied by an own vascular bundle. The vascular bundle strands of the cone scale and of the ovules do not fuse and enter the concentric stem bundle of the cone axis in separate strands. This situation corresponds quite well to the situation of a bract carrying a fertile axillary shoot. It seems that the seed scale was entirely reduced to its ovules, with no further vegetative structures belonging to it were visible. These results suggest the original cupressaceous seed cone was a more open and looser structure, which became strongly reduced to form the highly condensed compact seed cones of the extant Cupressus taxa.