The key difference between thallus and prothallus is that thallus is an undifferentiated filamentous gametophyte of algae, fungi, lichens, and some liverworts while prothallus is the heart-shaped gametophyte of pteridophytes such as club mosses, horsetails, and ferns.
Thallus is a non-differentiated plant body present in algae, fungi, lichens, and some liverworts. Prothallus, in contrast, is a heart-shaped thallus-like structure present in ferns. Both structures do not differentiate into root, stem or leaves. In prothallus, antheridia and archegonia are present. Hence, they only reproduce sexually. These specialized sex organs are not present in thallus.
CONTENTS
1. Overview and Key Difference
2. What is Thallus
3. What is Prothallus
4. Similarities Between Thallus and Prothallus
5. Side by Side Comparison – Thallus vs Prothallus in Tabular Form
6. Summary
What is Thallus?
Thallus is a non-differentiated plant body commonly found in algae. Hence, thallus does not have roots, stem, and leaves. Apart from algae, thallus can be seen in fungi, some liverworts, and lichens. The fungal thallus is the mycelium. However, in lichens, thallus is the vegetative body.
Figure 01: Thallus
Thallus is a gametophyte. It may be unicellular or multicellular. Furthermore, the gametophyte reproduces both sexually and asexually. It does not contain specialized sex organs antheridia and archegonia. Even though the thallus is undifferentiated in terms of anatomy, it is possible to observe visible and functional differences. As an example, brown algae have a thallus divided into three regions: hold fast, stipe and blades. The holdfast anchors the algae, the stipe supports the blades, and the blades carry out photosynthesis.
What is Prothallus?
Prothallus is a heart-shaped gametophyte present in pteridophytes. It is a 2-5 mm wide photosynthetic structure. Prothallus is attached to the soil with the help of rhizoids. Ferns undergo alterations of generation during the life cycle. It is a fluctuation between diploid and haploid stages of pteridophyte life cycle.
Figure 02: Prothallus
The diploid sporophyte is the dominant stage. It produces spores underneath and gives rise to the gametophyte which is a prothallus. Prothallus is a multicellular structure. It contains both antheridia and archegonia. Hence, it reproduces sexually. Antheridia produce gametes. These gametes swim towards the ova in the archegonia for fertilization.
What are the Similarities Between Thallus and Prothallus?
- Both thallus and prothallus are not differentiated into root, stem or leaves.
- Moreover, both are photosynthetic structures.
- Besides, they produce gametes for sexual reproduction.
- Also, both of them are gametophytes.
What is the Difference Between Thallus and Prothallus?
Thallus and prothallus are undifferentiated structures. Thallus is a filamentous structure while prothallus is a heart-shaped thallus like body. So, this is the key difference between thallus and prothallus. Moreover, though both are gametophytes, thallus reproduces both sexually and asexually, but prothallus only undergoes sexual reproduction. Thus, this is also a difference between thallus and prothallus.
Furthermore, antheridia and archegonia, which are specialized sex organs, are present in prothallus. But no such organs are available in thallus. Therefore, this is another difference between thallus and prothallus. Also, a further difference between thallus and prothallus is that the thallus is either unicellular or multicellular, but prothallus is only multicellular. Additionally, algae, fungi, liverworts, and lichens have a thallus-like structure while pteridophytes such as ferns, clubmosses, and horsetails have a prothallus.
Below info-graphic describes further on the difference between thallus and prothallus.
Summary – Thallus and Prothallus
Thallus and prothallus are undifferentiated structures in which true roots, stems or leaves are absent. Moreover, they are photosynthetic gametophytes. Thallus is a filamentous structure that we can commonly see in algae, fungi, liverworts, and lichens; they reproduce sexually and asexually. On the other hand, prothallus is a heart-shaped structure of pteridophytes. Additionally, prothallus is multicellular. Out of these two structures, only the prothallus contains antheridia and archegonia for sexual reproduction; however, sex organs are absent in the thallus. Thus, this summarizes the difference between thallus and prothallus.
Reference:
1. “Thallus.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 24 Feb. 2011, Available here.
2. “Prothallium.” Wikipedia, Wikimedia Foundation, 2 Mar. 2019, Available here.
Image Courtesy:
1. “Prothallus (Gametophyte) (8231437739)” By Paul K from Sydney, Australia – Prothallus (Gametophyte) (CC BY 2.0) via Commons Wikimedia
2. “A green algae (Ulva diaphana); leaf-like thallus and section Wellcome V0044187” By Weclome Collection (CC BY 4.0) via Commons Wikimedia