Tetramerous flower of Ludwigia octovalvis showing petals and sepals.

The calyx is part of the perianth of the flower. The perianth is composed of the sepals (collectively called the calyx) and the corolla (which is the outer part of the flower with the inner part of the perianth composed of the petals). The petals and sepals are usually differentiated into colorful petals and green sepals. But many flowers have colorful sepals and lack petals or the sepals and petals look similar and are often called tepals. The term tepal is usually applied when the petals and sepals are not differentiated and look similar or the petals are absent and the sepals are colorful. When the flower is in bud, the sepals enclose and protect the more delicate floral parts within. Morphologically they are modified leaves.

The number of sepals in a flower (called merosity) is indicative of the plant's classification: eudicots having typically four or five sepals and monocots and palaeodicots having three, or some multiple of three, sepals.

There exists considerable variation in form of the sepals among the flowering plants. Often the sepals are much reduced, appearing somewhat awn-like, or as scales, teeth, or ridges. Examples of flowers with much reduced perianths are found among the grasses. In some flowers, the sepals are fused towards the base, forming a calyx tube. This floral tube can include the petals and the attachment point of the stamens.

See also

Plant morphology

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