What are culms in plants of the Poaceae grass family?

In the Poaceae family, culms are the stems of the grass plant. These stems can be herbaceous or woody and range significantly in size, from approximately 2 centimetres in some grasses of severe climates to 40 metres in height in certain bamboos.1

Key characteristics of culms include:

• Structure: They are typically round in cross-section and are either hollow or filled with a spongy pith.1
• Growth: Unlike the stems of broad-leaved trees, grass culms do not develop woodiness through the annual production of lignified tissue layers. Instead, their structural rigidity is provided by blocks of tough, fibrous cells associated with the xylem, some lignification of parenchyma cells, and the silicification of the epidermis.1
• Habit: Culms can range from fully erect to prostrate and may grow solitarily or in dense clumps.1
• Support: While the culm itself provides the main axis, additional structural support is often provided by leaf sheaths, which encircle the internodes to help prevent bending.1