Pteridophytes (Gr. pteron= feather, phyton = plant) constitute the most primitive seedless vascular plants that reproduce by means of spores.
Hence, they are known as ‘vascular cryptogams’. Haeckel (1866) called these groups of plants as “Pteridophytes” because of their pinnate or feather like fronds (leaves).
Like reptiles (first true land animals that evolved after amphibian) they are considered as the first true land plants that evolved after bryophytes. Hence pteridophytes are some time called “Botanical Snakes” or “Snakes of plant kingdom.” They are also sometime called as “Amphibians is of plant kingdom” because like bryophytes they depend on an external source of water for fertilization.
There are about 11,000 species of living Pteridophytes are known ranging from small aquatic plant to giant tree ferns of tropical forests. Fossil records indicate that they evolved about 400 million years back i.e. in the Silurian period of late Paleozoic era. Hence late Paleozoic can be regarded as “Age of Pteridophytes.” Tippo (1942) has placed them in Tracheophyta or Tracheata because these plants first developed vascular tissues (xylem and phloem) where the tracheary elements appear like human trachea.
Salient Features of Pteridophytes:
1. Pteridophytes are the first true land plants.
2. They are seedless, vascular cryptogams.
3. Life cycle is heterologous diplohaplontic type.
4. Sporophyte is the dominant plant body while gametophyte is a small, simple prothallus.
5. Sporophyte has true roots, stem and leaves.
6. In xylem, trachea (vessels) absent and, in phloem companion cells absent.
7. Spores develop in sporangia are homosporous or heterosporous.
8. Sporangia are produced in groups (sori) on sporophylls.
9. Young leaves of sporophyte show circinate vernation.
10. Gametophyte develops small sessile antheridia and partially embedded archegonia with 4- rowed neck.
11. Sex organs multi-cellular and jacketed.
12. Embryonic stage present.
13. They have 4 sub-divisions:
(i) Psilopsida (Psilopsids)
(ii) Lycopsida (Clubmosses),
(iii) Sphenopsida (Horsetails) and
Economic Importance of Pteridophytes:
1. Ornamental value: Ferns arc grown as ornamental plants in gardens and homes for their attractive foliage.
2. Drug, Rhizomes and petioles of Dryopteris yield an antihelminthic drug.
3. Food. Sporocarps of Marsilea are rich source of starch and eaten for their nutritive value as food.
Classification of Pteridophytes:
Arnold (1947) classified Division Tracheophyta (vascular plants) into four Sub-Divisions as given below:
However, Oswald Tippo (1942) recognized the above mentioned four Sub-Divisions as Sub- phyla of vascular cryptogams.
Distinguishing features of these Sub-Divisions/ Sub-Phyla are given below:
(I) Sub-Division Psilopsida:
1. These are the oldest known vascular plants. Most of them have become extinct (e.g., Rhynia, Horneophyton). Only two living species, Psilotum and Tmesipteris, are now available.
2. Plant body is very simple and does not show much differentiation.
3. Dichotomously branched rhizome takes the place of roots.
4. Stem or “axis” is aerial, but either naked or have small spirally arranged leaves.
5. Sporangia are directly borne on the stem (i.e., cauline). Either terminal or lateral.
(II) Sub-Division — Lycopsida:
1. Plant body more advanced and shows differentiation into root, stem and leaves.
2. Leaves are microphyllous (small) having a single unbranched vein in the midrib region.
3. Sporangia are borne in the axil of the fertile leaves (sporophyils).
4. Sporophyll form compact strobili (singularstrobilus). e.g., Lycopodium, Selaginella.
(III) Sub-Division —Sphenopsida:
1. Plant body still more advanced and shows differentiation into nodes and internodes like higher vascular plants.
2. Leaves microphyllous, and arise in whorls at each node.
3. Sporangia develop on sporangiophores which form compact cones at the apex of fertile branches (e.g., Equisetum).
(IV) Sub-Division – Pteropsida (Ferns):
1. Plant body shows much advancement towards higher vascular plants, and is well differentiated into root, stem and leaves.
2. Leaves also show great advancement, and are megaphyllous (large) and pinnately compound.
3. Sporangia develop on the ventral surface of the sporophyils, and usually aggregated into sori (e.g., Dryopteris, Pteris, Pteridium, Polypodium etc.)