Peristome

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A diagram showing the location of the peristome on a Sarracenia (North American) pitcher plant.

The word peristome is derived from the Greek for 'around a mouth', and is a term used to describe various structures in plants that surround an opening to an organ.

In bryophyte mosses, the peristome is a specialized structure in the sporangium that allows for gradual spore discharge, instead of releasing them all at once.

In pitcher plants, the peristome is a reflexed ring (or partial ring) of tissue that surrounds the entrance to the digestive tube in these plants. It often (for example in Cephalotus) possesses sharp, overhanging 'teeth' which aid in prey retention. It is often studded with nectar secreting glands, hence its popular name, 'nectar roll'.

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