Difference between Protonema and Prothallus

The protonema and prothallus are structures seen in primitive plants. The key difference between both these structures is that protonema constitutes the first stage of development in liverworts and mosses, while prothallus is seen in pteridophytes and is its gametophyte. The structural difference seen in them is that protonema is thread-like, while prothallus resembles that of the shape of a heart.

Protonema

  • In the life cycle of mosses, these are thread-like chains of cells forming the initial phases of the development of the gametophyte.
  • Initially, when moss grows from a spore, it starts as a germ tube lengthening and branching into a filamentous complex referred to as protonema developing into a leafy gametophore, the adult form of a gametophyte in the bryophytes.
  • Protonemata is the trait of all the mosses and a few liverworts. However, these are not seen in the hornworts.
  • In mosses, the Protonemata comprises two types of cells – caulonemata and chloronemata.

Prothallus

  • In the life of a pteridophyte, the prothallus is typically the gametophyte phase.
  • It develops from the germinating spore and is heart-shaped.
  • These are short-lived structures, usually have a width of 2–5 millimetres with several rhizoids found underneath along with the sex structures – antheridium and archegonium.
  • In the early growth stages, the sporophyte grows out of the prothallus, relying on it for nutrition and water supply; however, it develops into a new independent fern. Eventually, it produces new spores, which grow into new prothallus hence completing the life cycle.

Key Difference between Protonema and Prothallus

The table below depicts the difference between Protonema and Prothallus.

Protonema

Prothallus

What is it?

Filamentous thalloid structures of the gametophytes seen in some liverworts and mosses

These are gametophytes of the pteridophytes

Where can it be seen?

Mosses and in some liverworts

Pteridophytes

Appearance

Thread-like appearance

Heart-shaped appearance

What does it give rise to?

Gametophores – leafy shoots

Female and male sex structures

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