Question

How are Pteridophytes classified?

Answer 1

Hint: A pteridophyte is a free-sporing vascular plant with xylem and phloem. On the basis of nature and relation of leaf and stem vascular anatomy and position of sporangia, they are classified into four main classes - Psilopsida, Lycopsida, Sphenopsida and Pteropsida.

Complete answer:
A pteridophyte is a free-sporing vascular plant with xylem and phloem. Pteridophytes are often referred to as "cryptogams," meaning that their means of reproduction are secret since they do not grow flowers or seeds. On the basis of nature and the relation of leaf and the stem vascular anatomy and position of sporangia, they are classified into four main classes - Psilopsida, Lycopsida, Sphenopsida and Pteropsida. The characteristic features of these four divisions are as follows:

Psilopsida:
- The most primitive type among the four.
- They have photosynthetic stems and are dichotomously branched.
- They have rhizoids.
- Most of them don't have leaves.
- The sporophyte is homosporous synangium.
- Examples- Psilotum and Tmesipteris.

Lycopsida:
- They are commonly known as club moss.
- They have a well-differentiated plant body with adventitious root, stem, rhizophores and leaves.
- The sporophyte is homosporous or heterosporous.
- Examples – Selaginella, Lycopodium

Sphenopsida:
- They are commonly known as horsetail.
- They have roots arising from nodes of the underground rhizome, stem and scaly leaves.
- The sporophyte here is homosporous sporangia and borne on strobili.
- Examples – Equisetum.

Pteropsida:
- They are commonly known as fern.
- They too have a well-differentiated plant body with roots, stem and leaves.
- The sporophyte is either homosporous or heterosporous.
- Their antherozoids are multi-flagellate.
- Examples- Pteris, Dryopteris, Adiantum.

Note: Pteridophytes are considered as first true land plants and are an important division in plant kingdoms. For a very long-time vascular plants were usually divided into pteridophyte and spermatophyte that was based on the prior assumption that the former lack seeds while the latter can produce seeds. But with the discovery of pteridophytes – seed bearing ferns – this artificial classification broke down.