Difference Between Operculum and Peristome

The key difference between operculum and peristome is that operculum is a cap-like covering found in some plants, mosses and fungi while peristome is a ring of tooth-like appendages around the opening of the capsule of mosses.

Mosses are nonvascular plants belonging to phylum Bryophyta. They are flowerless plants that don’t have true roots. They grow in damp or shady areas and reproduce by spores. Mosses produce spores inside the spore-bearing capsules or sporangia. The spore-bearing capsule has an apical lid which is called an operculum. It also has a ring of tooth-like appendages surrounding the mouth of the capsule. This is called the peristome. Both operculum and peristome are important structures of mosses.  When the operculum falls off, peristome is exposed to the outside.

CONTENTS

1. Overview and Key Difference
2. What is Operculum
3. What is Peristome
4. Similarities Between Operculum and Peristome
5. Side by Side Comparison – Operculum and Peristome in Tabular Form
6. Summary

What is Operculum?

The operculum is the covering or cap-like structure found mainly in mosses. Operculum closes the spore-bearing capsule of mosses. Therefore, it is an apical lid that covers the capsule. Moreover, operculum is present in flowering plants as well as in fungi. In flowering plants, the formation of operculum happens by the fusion of sepals or petals. Once the fruit is mature, operculum detaches from the fruit.

In some plants, there are two opercula; an outer operculum and inner operculum. In mosses, when the sporangia become ready to release spores, the operculum falls off and the peristome is exposed and gradually releases spores to the environment. In fungi, opercula are present in ascomycete fungi. They have an operculum on the top of each ascus.

What is Peristome?

The peristome is a ring of tooth-like appendages surrounding the opening of the capsule of mosses. These tooth-like appendages are small and pointed. Peristome teeth usually surround the mouth of the sporangium in mosses. It is a specialized structure which is important in the gradual release of spores in mosses, rather than releasing them at once. Hence, peristome influences the release of spores from sporangia in mosses. In simple words, peristome controls the release of spores for an extended period of time.

Peristome teeth usually respond to slight changes in moisture and pulsate inward and outward, carrying spores out of the sporangium. Peristome can be seen when the lid is removed.  Fungi, some plants and some gastropods also have peristomes.

What are the Similarities Between Operculum and Peristome?

• Operculum and peristome are two structures found in spore-bearing capsules of mosses.
• Peristome can be seen once the operculum is removed.
• Both structures are often found together.
• Some fungi and some plants also have opercula and peristomes.

What is the Difference Between Operculum and Peristome?

Operculum is a cap-like structure that covers capsules or spore-bearing structures of plants, mosses and fungi. Peristome, on the other hand, is a ring of tooth-like appendages that surrounds the mouth of capsule or spore-bearing structures of mosses, flowering plants and some fungi. So, this is the key difference between operculum and peristome. Operculum covers the opening of the sporangium or capsule while peristome controls the gradual release of spores from the sporangium.

Below infographic summarizes the difference between operculum and peristome.

Summary – Operculum vs Peristome

Operculum is a lid or cap-like structure that covers the opening of capsule or spore-bearing structure. In contrast, peristome is a ring of tooth-like appendages that surrounds the mouth of a capsule or spore-bearing structures of plants, mosses and fungi. Thus, this is the key difference between operculum and peristome. Both structures are often found together. Functionally, operculum covers the sporangia or capsules while peristome controls the release of spores.

Reference:

1. “Peristome”. En.Wikipedia.Org, 2020, Available here.
2. “Operculum: Definition & Types.” Study.Com, 2020, Available here.

Image Courtesy:

1. “Eucalyptus erythrocorys operculum” By Hesperian – Own work (CC BY 3.0) via Commons Wikimedia
2. “Bryum capillare peristome” By Des_Callaghan – Own work (CC BY-SA 4.0) via Commons Wikimedia