The Pteridophytes comprise of the lower vascular plants (Trachaeophyta) which show distinctly vascular, independent sporophytic plants arising from embryos (Embryophyta or Cormophyta) which are not enclosed within any ‘seed’ structure. These alternate with independent gametophytes which are almost bryophytic in appearance and bear antheridia and archegonia (Archegoniatae).
These lower vascular plants are called the Pteridophytes or the Pteridophyta. Although numerically much below the Bryophytes (there are 23,000 living species in about 900 genera of Bryophytes against about 10,500 species in some 400 genera of living and fossil Pteridophytes) the Pteridophytes claim a special position as the first land plants forming forests.
But the idea of the relative position of this group Pteridophyta within the Plant Kingdom has greatly changed in recent days.
The artificial concept of dividing the Plant Kingdom into the Cryptogams and the Phanerogams persisted throughout the 19th century but was practically abandoned in the twentieth. Even during the 19th century we find abandonment of the idea of considering the Cryptogams as a group.
Auguste Pyramos de Candolle, who coined the term ‘Taxonomy’ (1813) divided the Plant Kingdom into the Cellulares (Thallophyta and Bryophyta) and the Vasculares (Vascular Plants) in 1819.
Thus, de Candolle was the first to recognise that the Pteridophytes should rather be linked with the higher plants than with the artificial Linnaen group of Cryptogams.
Stephen Endlicher divided the Plant Kingdom into Thallophyta and Cormophyta raising the Bryophytes also to the higher Cormophytes. In the latter part of the 19th century, A.
Engler also supported Endlicher and stated that it was much better to divide the Plant Kingdom into two groups: Thallophyta and Embryophyta.
Our concept of both the Thallophyta and the Embryophyta has undergone much change during the 20th century.
One idea had been to consider the Pteridophyta as a division of the Plant Kingdom parallel to the three other divisions—Thallophyta, Bryophyta and Spermophyta. Jeffrey (1902) first proposed that the original units be abandoned and the vascular plants be divided into two stocks the Lycopsida (Lycopods and Equisetums) and the Pteropsida (Ferns, Gymnosperms and Angiosperms).
Bessey (1911) divided the whole Plant Kingdom directly into 14 phyla, the 9th, 10th and 11th of which comprise of the Pteridophytes.
Engler, in the 1936 edition of the Syllabus similarly divides the Plant Kingdom directly into 14 Abteilungen (Divisions) the first 12 of which are Thallophytes, the 13th is Archegoniatae (or Embryophyta Asiphonogama) and the 14th Embryophyta Siphonogama (Gymnosperms and Angiosperms).
The Archegoniatae are again divided into two subdivisions (Unterab- teilungen): Bryophyta and Pteridophyta.
In 1935, Sinnott proposed the term ‘Trachaeophyta’ to include all the Vascular Plants. Tippo (1942) suggested that the Plant Kingdom be divided into two subkingdoms Thallophyta and Embryophyta and the latter be divided into two phyla—Bryophyta and Trachaeophyta.
Takhtajan (1950) coined the term ‘Telemophyta’ to rename the Embryophyta in view of the Telome Theory. Bold (1957) suggested dividing the Plant Kingdom into three subkingdoms Thallophyta, Bryophyta and Trachaeophyta.
Consideration of the Trachaeophyta as a distinct group emphasises the most important character acquired by the land plants—the vascular bundles. The Trachaeophytes, no doubt, show certain characters embodying the main trend of evolution since the land habit was acquired. But, this is too vast a group to be considered as a single division as a vast majority of the modern plants are included here.
Moreover, Takhtajan (1953) and others do not think that the Bryophyta should be separated from the Trachaeophyta, the former being a possible derivative of the latter. This point has now been emphasised by Cronquist, Takhtajan and Zimmermann (1966).
The living Pteridophytes distinctly show four groups of plants representing four lines of evolution. The first three of these lines—the Psilotums, the Lycopods and the Equisetums—ended blindly. The last—the Ferns-evolved further into the Gym- nosperms and the Angiosperms.
Because of this, Bessey (1911) proposed the abolition of the old taxon Pteridophyta replacing it by three divisions (‘phyla’)— Pteridophyta -proper (ferns), Calamophyta and Lepidophyta.
Since then other divisions have been added, most important of which is the division Psilophyta.
Some systematists have retained Pteridophyta as a division calling the main taxa ‘classes’ (some have called the main taxa ‘phyla’, a term used in Zoology but cannot be retained in Botany according to International Rules of Botanical Nomenclature) while others have deleted the Pteridophyta as a taxon raising the lower taxa themselves into divisions.