ligule

A ligule is a small outgrowth at the junction of the leaf blade and leaf sheath in most grasses (family Poaceae). It is located on the inner side where the blade meets the sheath and marks the boundary between these two leaf parts. The ligule can be membranous and translucent, or short and hairy, and may extend as a thin flap or fringe along the blade base. Some grasses have a very short or nearly invisible ligule, while others possess a distinctive, well-developed structure.

Functionally, the ligule acts as a barrier that helps prevent water, dust, and pathogens from entering the sheath around the stem. It may also help reduce moisture loss at the leaf base and contributes to the organization and sealing of the leaf sheath around the culm.

In plant identification and taxonomy, the presence, absence, and particular form of the ligule are important diagnostic characters. Ligule morphology varies among genera and species, so its length, texture, and whether it is membranous or hairy are often used in keys and descriptions to differentiate grasses.

The ligule is distinct from other basal leaf structures such as the auricles, which in some grasses wrap around the stem. The ligule specifically denotes the boundary between blade and sheath rather than a feature at the leaf margin.