Morphology and anatomy of needle-leaves and cladode-like structures in Abies firma Siebold & Zucc. (Pinaceae, Coniferales) and their evolutionary relevance

Abstract

Needle-leaves and untypical leaf structures in Abies firma were investigated. Among Abies needle-leaves are generally described as being supplied with two vascular bundles surrounded by a common bundle sheath. However, the results indicate that needle-leaves of Abies firma are always supplied with only a single vascular bundle, which is strongly interrupted by parenchymatic bands in the middle part of the lamina. This parenchyma lacks in distal and proximal parts. Thus, the leaf-vasculature among Abies is not open dichotomous as is generally assumed. Studies of the detected untypical leaf structures which seem quite similar to cladodes of Sciadopitys - and Phyllocladus have shown that they are formed exclusively by congenitally fused needle-leaves. This fusion takes place in the early stage of development favored by the very broad leaf bases. Within a parastichy the primordia of two, three or four directly neighbored leaves are in physical contact. Secondary, they fuse completely with their lateral margins. Thus, they represent contact parastichys of only some leaves within a helical line at the shoot axis. Thus, these untypical leaf structures have no evolutionary relevance in respect to the understanding of the interfamilial phylogeny. Nevertheless, they help towards a better understanding of cladode-formations in general.