In which plant is there no distinction between tunica and corpus?

The distinction between tunica and corpus is absent in gymnosperms and certain lower vascular plants. In most angiosperms (flowering plants), the shoot apical meristem shows a clear zonation into outer tunica layers (where cells divide anticlinally) and inner corpus (where cells divide in all planes). However, in gymnosperms like pine, spruce, and other conifers, the apical meristem is organized differently and doesn't show this distinct tunica-corpus arrangement. Instead, gymnosperms typically have a more uniform cytohistological zonation pattern. This fundamental difference in shoot apex organization reflects the evolutionary divergence between gymnosperms and angiosperms and affects how their shoots develop and differentiate.