How do grass stems differ from the woody trunks of trees?

Grass stems, often called culms, differ significantly from the woody trunks of trees in their internal structure and growth patterns.

Structural Differences

• Vascular Arrangement: In woody dicot trees, vascular bundles are arranged in a ring, allowing for the development of a vascular cambium that produces secondary xylem (wood) and bark to increase girth. In contrast, grasses are monocots with vascular bundles scattered throughout the stem. These bundles are "closed," meaning they lack a vascular cambium and cannot produce wood in the same manner as trees.123
• Rigidity: While trees rely on secondary xylem for structural strength, grasses achieve rigidity through other means, such as the presence of tough, fibrous cells associated with the xylem, the lignification of parenchyma cells, and the silicification of the epidermis. Additionally, grass leaf sheaths provide essential support to help the stem stand erect.4

Growth Patterns

Grasses grow by cell division and enlargement at the basal point of the stem, whereas trees utilize apical meristems and lateral cambia to increase both height and diameter.452