Involucre

An involucre is a whorl or collection of bracts that surrounds or subtends a flower or inflorescence. It functions as a protective envelope for developing flowers and may be persistent or deciduous as the bloom matures. The term is used broadly in botany to describe bracteal structures that envelop a floral unit, and it is distinct from the calyx or from individual leaf-like bracts that accompany a single flower.

In the family Asteraceae, the involucre is a well-defined structure formed by the phyllaries, the bracts that encircle the capitulum (the flower head). These phyllaries are often arranged in one or more series and can vary in size, shape, color, and texture. The involucre may be short and nearly closed or elongated into a cup-shaped or scaly envelope. In some species, the involucres persist around the mature fruit and can influence the appearance of the head. The characteristics of the involucre, including the number of phyllaries and their persistence, are important diagnostic features in identifying and classifying genera and species within the group.

Outside Asteraceae, involucres can occur as rings or clusters of bracts at the base of an inflorescence or around a floral unit in various plant groups. The term is sometimes contrasted with the epicalyx, a separate whorl beneath the calyx in certain plants, but the involucre broadly refers to a protective assemblage of bracts surrounding or under a floral structure.