Glumes

Glumes are the pair of bracts at the base of a grass spikelet. In most grasses, each spikelet is subtended by two glumes—the lower glume and the upper glume—that enclose the florets and their inner bracts, the lemma and palea. The two glumes can be similar in size or differ, and they may be persistent or deciduous after flowering. Their size, shape, venation, and surface features such as hairs or teeth are often important in the taxonomy and identification of grasses.

Functionally, glumes protect the developing florets before and during anthesis and contribute to the structural integrity of the spikelet. In some species they may aid in seed dispersal when spikelets mature. After seed development, the glumes may remain attached to the seed or drop away, depending on the species.

Distinction from the inner bracts is important: the palea and lemma are the inner bracts that enclose each individual floret, while the glumes form the outer envelope of the entire spikelet. In agricultural contexts, glumes are frequently removed during threshing for many cultivated cereals, though they can be retained in some traditional grains and wild grasses.

Glume characteristics, including number, size, and morphology, are commonly used in grass systematics to differentiate genera and species. The term derives from the Latin gluma, meaning husk or husk-like covering.