1. Volume 27, Issue 17, Pages R878-R882 (September 2017)
Radial plant growth 
Nina Tonn, Thomas Greb 
Current Biology 
Volume 27, Issue 17, Pages R878-R882 (September 2017)
DOI: /j.cub
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2. Figure 1
The evolution of land plants and the diversity of radial growth.
Today’s land plants have evolved from freshwater charophytes (green algae). Early land plants were similar to extant bryophytes (liverworts, hornworts and mosses). The invention of a primary vascular system gave rise to larger species like lycophytes (e.g., clubmosses) and ferns. Modern seed plants include gymnosperms and angiosperms, all of which share a common ancestor regarding radial growth. Among angiosperms, dicotyledonous species, for example, cacti (A), lianas (B), and beets (C), show anomalous radial growth (see text for details). Monocotyledonous species, including the grasses (D), have lost the ability to grow radially but reinvented this skill in some cases (E). (Photographs taken from
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3. Figure 2 The vascular cambium is essential for radial growth.
Thickening of vascular plants is regulated by stem cell-like tissues, including the vascular and the cork cambium organized in concentric cylinders. The schematic cross-section illustrates how the vascular cambium produces wood (secondary xylem) toward the inside, and bast (secondary phloem) toward the outside. Additionally, the cork cambium produces phelloderm inwards and cork outwards, thereby replacing the primary epidermis. Production of secondary vasculature is performed by cambium initials (CIs) in the centre of the cambial zone. By periclinal cell divisions, they give rise to still proliferating derivatives differentiating into xylem or phloem. As illustrated, xylem is usually composed of tracheary elements (tracheids, vessel elements, T), fibres (XF) and parenchyma cells (XP). Phloem cells include enucleated sieve elements (SEs), adjacent companion cells (CC) and parenchyma cells (PP). Additionally, the formation of phloem fibres (PF) is found in many species. More initials are produced by anticlinal cell division during the increase of the circumference of the cambial zone.
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4. Figure 3
Importance of primary and secondary plant thickening for food production.
Increased thickening of plant shoots and roots has been bred for during the domestication of crop species. Examples include potatoes (A), red beets (B), cassava (C), kohlrabi (D), sugar beets (E), and carrots (F). (Photographs taken from
Current Biology  , R878-R882DOI: ( /j.cub )
Copyright © 2017 Elsevier Ltd Terms and Conditions