ligule

A ligule (from Latin: ligula "strap", variant of lingula, from lingua "tongue") — is a thin outgrowth at the junction of leaf and leafstalk of many grasses (Poaceae) and sedges or a strap-shaped corolla, such as that of a ray floret in plants in the daisy family.

Poaceae and Cyperaceae

The ligule is found at the inner base of the leaf between where the leaf attaches to the main stem and the stem itself. It may take several forms but is commonly some form of translucent membrane or a fringe of hairs. The membranous ligule can be very short 1–2 mm (Kentucky Bluegrass, Poa pratensis) to very long 10–20 mm (Johnson grass, Sorghum halepense), it can also be smooth on the edge or very ragged. Some grasses do not have a ligule, for example barnyardgrass (Echinochloa crusgali).

A ligule can also be defined as a membrane-like tissue or row of delicate hairs typically found in grasses at the junction of the leaf sheath and blade. The ligule appears to be a continuation of the leaf sheath and encircles or clasps the stem as does the leaf sheath. There are three basic types of ligules: membranous, a fringe of hairs (ciliate), and absent or lacking. Most grasses have ligules, and the shape, length, and appearance of the ligule margin provide consistent characters for separating genera and some species of grasses.

In grass-like plants such as sedges (Cyperaceae) and rushes (Juncaceae), ligules are usually absent or poorly developed.

Asteraceae

Ray floret, typical for flowers of the family Asteraceae:
A. ovary
B. pappus
C. theca
D. ligule
E. style with stamen

Ligules are also present in some non-grass species such as members of Asteraceae family. The ligule is the tongue-like part of a ray floret.

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