True Indusium vs. False Indusium

Main Difference

The main difference between True Indusium and False Indusium is that True Indusium is a delicate membrane that arises from the lower side of the pinnae while covering the sorus of sporangia acts as a protection against the external environment, whereas, false indusium is formed by the curving margins or pinnae that protects and covers the marginal sorus.

Difference Between True Indusium and False Indusium

Comparison Chart

True Indusium vs. False Indusium

True indusium covers the sorus of sporangia as these sori are responsible for the reproduction of their species; however, false indusium protects the marginal sorus. True indusium is a membrane that arises from the lower side of the pinnae and covers the sorus of sporangia, whereas false indusium is formed by the curving margins or pinnae that protects the marginal sorus.

True indusium arises from the lower side of the pinnae to give protection to the sorus of sporangia from the external environment and unfavorable conditions that sorus is required to be protected from, however, in case of false indusium the indusium arises from the upper side of the margins of the pinnae as these are the curvy margins of the leaflets acting as the protecting cover for marginal sorus from the external environment.

True indusium is a separate and unique growth of pinnae while structural origin is still unclear as it constitutes of less papery covering, on the other hand, false indusium is caused by rolled over leaflets or pinnae.

True indusium is an epidermal growth arising; on the other hand, false indusium is curvy margins formed as a result of their growth from the lower margin of leaflets. True indusium can be seen in Dryopteris, etc., whereas False indusium can be seen in Pteris, Adiantum, etc.

What is True Indusium?

True indusium is a membrane that arises from the lower side of the pinnae or the leaflets in ferns that covers the sorus of sporangia. These membranes’ origination is still unknown in the case of true indusium. Sori is a terminal vein on, but more often, it is a True indusium arises from the lower side of the pinnae to fulfill its purpose, i.e., protecting the sorus of sporangia. It is a separate and unique growth of pinnae, while structural origin is still unclear as it constitutes less papery covering.

True indusium is an epidermal growth arising from the lower margins. Complex aggregation of sporangia is known as the sorus, which is the meristematic area of the plants as it is a region of new cell growth that produces sporangia while preforming activities over several weeks. When sori develop on leaves of the house of fern, they are mostly mistaken for insects or a fungal disease rather than be recognized as reproductive organs of plants.

The stages in the progressive evolution of sori involve simple cluster formation of sporangia, then graduate clusters of sporangia, then mixed clusters of sporangia. The significance of this change is related to the duration of spore production, the mixed character of more advanced sori extend the period beyond that of simple sporangia and thus simultaneously mature sori. Sori have traditionally provided the most important characters for classification of ferns as many unrelated sori are classified together just based on their converging characteristics to be now classified together.

As the sporangial clusters are to be protected from drying, exposure with the external environment, and other hazards, this process is achieved by the formation of sori in grooves or pockets by the production of various forms of covers. The true indusium is a unique formation, and its structural origins are not clear as it constitutes less papery covering over the sorus.

True indusium can be seen in Dryopteris etc. Approximately one-third of fern species tend to have paraphyses of one type or the other, these paraphyses are the sterile hairs or scales that intermix with sporangia, and like sporangia, they are believed to perform a function like indusa, i.e., they tend to perform a protective function like indusia. Unlike indusia, these paraphyses are hair-like modifications that arise among the sporangia or stalk or capsule.

A series of type of indusium is found among the members of family Cyatheaceae are the ones that have a shape like a cup. This cup arises around the base of the sorus, and it keeps closing the sorus until the sporangia are mature. In some of the genera like Dennstaedtia, Dicksonia, and Hymenophyllum, these marginal sori are protected by a two-lipped or valvate indusium. Indusia also tend to fuse when these sori fuse laterally to form a continuous line or coenosori.

What is False Indusium?

False indusium is formed by the curving margins of pinnae or leaflets that protect the marginal sorus. As the sporangial clusters are to be protected from drying, exposure with the external environment, and other hazards, this process is achieved by the formation of sori in grooves or pockets by the production of various forms of covers. False indusium protects the marginal sorus, unlike the true indusium where membrane arising from the lower side of pinnae protects the sorus of sporangia.

False indusium arises from the upper side of the margins of the pinnae. These margins arise from the curving endings of the leaflets or pinnae to fulfill their purpose of protecting the marginal sorus from environmental conditions as sorus is a cluster of sporangia, which contains spores for their formation. These sori are commonly found in ferns and fungi.

In lichen and other fungi, the sorus is surrounded by an external layer, while in red algae, this layer may take a form of depression into the thallus. In ferns, these surrounding external layers form a yellowish or brownish mass on the edge of the utter side of a fertile frond. In some species, these sori are protected during their development by a scale or film of tissue, which is known as indusium.

This indusium forms an umbrella-like cover. These sori occur on sporophyte generation, the sporangia within their development produce haploid meiospores. These sporangia as they mature, the indusium which has the responsibility for its production until development shrivels so that the release of these pores in unimpeded. Then these sporangia upon living off of the indusium burst and then release the spores.

The location, shape, and arrangement of these sori are often valuable clues while identifying the fern taxa. These sori can be in circular or linear shape. They can be arranged in rows, either parallel or oblique to costa or randomly. Their location can be found marginal or set away from the margin on the frond lamina. While identifying texa of a fern, the presence or absence of indusium is also used.

One of the protections for grooves is as found to be false indusium. It is a rolled overleaf under which sporangia form and mature. This false indusium gives protection to the sporangia from its formation until maturity. By protecting the sporangium, false indusium fulfills its purpose.

False indusium is not a separate and unique growth of pinnae where the structural origins were still unclear as it constitutes of less papery covering, False indusium is the curvy margins that are formed as a result of their growth from the lower margin of leaflets. False indusium can be seen in Pteris, Adiantum, etc.

Conclusion

True indusium is a sensitive membrane that emanates the lower side of the pinnae that acts as a protection and covers the sorus of sporangia, whereas false indusium is formed by the bending margins of pinnae or leaflets that protects and covers the marginal sorus.