What Are Thallophytes in Biology?

Thallophytes are all the non-flowering plant organisms that do not present differentiation of plant organs, such as roots, leaves or true stems. From the group Thallophyta, Thallophytes are made of a textured tissue known as thallus. These organisms are made from connected thallus tissue which create functional and morphological units that work together. In doing so, they fulfill the functions of any living being such as feeding and reproduction.

It is important to emphasize that the term ‘thallophyte’ is a taxonomic categorization that is not always used by all botanists or biologists. They are classified as a group of ‘lower plants’ which are contrasted with more complex plant species known as ‘higher plants’. Thallophyta is also used to refer to a very diverse range of organisms, so it is often replaced with a more specific categorization.

However, looking at the characteristics of thallophytes, we can better understand the range of species within the kingdom Plantae, as well as some of those without this kingdom. This includes complex and more simple organisms such as thallophytes.

The body of thallophytes is made of the thallus. It is composed of groups of cells which are not differentiated into organs. The components are integrated with each other, but do not differentiate into tissues specialized in any particular function. The lack of differentiation is a sign of more primitive organisms, but no less important for ecosystems.

Thallophytes are multicellular, consisting of several cells brought together. All cells work together to fulfill basic functions, remaining in communication with each other as they do so. They do not have locomotor capacity. For this reason, they remain floating in the water or attached to some substrate. This is in contrast to flowering plants, for example. Flowers will turn towards the sun, but thallophytes are incapable of doing so.

The set of cells can be organized in many varied ways. Some examples are the following:

• Filamentous thalli: the division of cells forms filaments with septa between them.
  
  
• Lamellar thalli: there are two surfaces, one on the back of the other. They are flat and symmetrical.
  
  
• Siphonocladal thallus: it can be observed when the filaments have several nuclei, increasing the organizational complexity and approaching the tissues.
  
  
• Plectenchymatic or pseudoparenchymatic thalli: the filaments intertwine with each other, forming something similar to a tissue, but not exactly a true one.
  
  
• Parenchymatic thalli: in this case tissues do form by aggregation of ordered cells.

In addition to the aforementioned lack of organs, they also do not have vascular tissues with xylem or phloem. These are the tissues responsible for transporting water, minerals and sap within the plants. Being non-vascular plants means thallophytes find it difficult to regulate water and they are vulnerable to changes in humidity. This is why thallophytes live in water or are extremely dependent on it.

As stated above, thallophytes are considered ‘lower plants’. This is a term that helps us better understand this classification, but is not so appropriate. This is because not all thallophytes are photosynthetic and not all are true plants.

To better understand how these non-animal organisms are classified, you may want to take a look at our related article on what is the kingdom Monera?

Now that you know what a thallophyte is and its characteristics, we will introduce you to the groups that make up this categorization.

Algae

They are organisms that always have chlorophyll and that can photosynthesize to obtain their food. They live inside water and do not contain structures that give them rigidity when outside of it. Neither do they have structures that protect them from drying out.

Its organization can be filamentous, with the development of cells that divide one over another to form filaments, or parenchymatic, in which broad tissue-like surfaces are formed. The latter is the case for proliferations of red algae. Some algae may also have thalli with knots, which are not properly tissue differentiations, but are very close.

Learn more about the classification of algae with our article on the kingdom Protista.

Fungus

Fungi are organisms that lack chlorophyll and need external sources to obtain their food. They decompose organic matter and can also live as parasites on plants or animals. This means they are types of heterotrophs.

In this case, the organization of fungi is filamentous, where the hyphae septate to form thin filaments composed of cells. The set of filaments in fungi is known as mycelium. The mycelium can develop above ground into a so-called fruiting body from which the reproductive spores will emerge.

Learn the structure of fungi in our related article.

Lichens

Lichens are very interesting organisms that consist of a symbiotic association of algae and fungi, combining feeding by chloroplasts with that from inorganic matter. They are a combination of the two groups we just reviewed. This symbiosis forms very thin, disc-shaped structures, which can grow on a wide variety of surfaces such as tree bark or rocks. Here it is evident that it is an accumulation of cells that do not form differentiated organs.

Lichens are a type of cryptogamic plant which you can read about with thedailyECO.

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