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.
2. How different are pteridophytes from bryophytes regarding substance transport?
Pteridophytes are tracheophyte (vascular) plants, meaning that they have tissues specialized in the conduction of water and nutrients. Bryophytes are nonvascular plants. Therefore, in pteridophytes, the substance transport is carried out through vessels whereas, in bryophytes, that transport occurs via diffusion.
3. Why are pteridophytes better adapted to dry land than bryophytes? Were pteridophytes always less abundant than phanerogamic plants?
Although bryophytes and pteridophytes have gametes tha depend on water for fertilization, the emergence of conducting vessels in this last group facilitated life in a terrestrial environment. The conducting vessels of pteridophytes collect water from moist soil and distribute it to the cells. Bryophytes do not have this option and depend entirely on the water that reaches the aerial part of the plant and, as a result, they need to live in humid or rainy places.
Before the evolutionary development of phanerogamic plants (plants that have seeds), pteridophytes predominated in the terrestrial environment. The large pteridophyte forests of the Carboniferous period (named after the pteridophytes) are responsible for the formation of coal deposits, mainly in Europe, Asia and North America. The Carboniferous period occurred between 290 and 360 million years ago and was part of the Paleozoic Era.
4. What is the evolutionary importance of pteridophytes?
As the first tracheophytes, pteridophytes were also the first plants to extensively colonize the terrestrial environment, forming forests. They also constituted an important food source for terrestrial animals. Because of their conducting vessels, they could be larger, a feature that phanerogamic plants inherited from them.
The Parts of Fern
5. What are the main parts of ferns?
Ferns are composed of small roots that shoot downwards from the rhizome (the stem, often horizontal). Fronds also arise from the rhizome. On the back side of each leaf of the plant, there are small dust-like dots called sori (singular, “sorus”, also known as “seeds”).
The Life Cycle of Pteridophytes
6. What type of life cycle is followed by pteridophytes?
Like all plants, pteridophytes go through a diplobiontic (alternation of generations, or metagenesis) life cycle.
7. Why are pteridophytes more common in humid places?
Pteridophytes are more common in humid places because they depend on water for their gametes to fertilize one another. In humid environments, their reproduction is more intense and they proliferate.
8. In what structure of the adult fern can cells undergoing meiosis be found?
In these plants, meiosis takes place within structures called sori, small dust-like brown dots that line the underside of fern leaves. Sori contain sporangia where reproductive cells undergo meiosis and where spores are produced.
9. What is the prothallus of pteridophytes?
The prothallus is the pteridophyte gametophyte (the haploid individual that forms gametes). The gametophyte develops via mitosis from a spore.
- Pteridophytes Review - Image Diversity: prothallus
10. How are gametes formed during the pteridophyte life cycle, by mitosis or meiosis? What type of meiosis occurs in pteridophytes?
In pteridophytes, gametes are produced via mitosis from special cells of the gametophyte. As with all plants, in pteridophytes, meiosis is sporic, meaning that cells of the sporophyte undergo meiosis and generate spores that then develop into the gametophyte via mitosis.
11. What is the lasting form of pteridophytes, the gametophyte or the sporophyte? How can this be compared to bryophytes?
The lasting form of pteridophytes is the diploid (2n) sporophyte (the fern itself, for example). In bryophytes, the lasting form is the gametophyte (n).
12. What is a xaxim?
Most pteridophytes have underground stems parallel to the substrate called rhizomes. Xaxim is a type of pteridophyte with an aerial stem that is generally perpendicular to the soil and from which hundreds of roots arise to absorb water from the environment. Xaxim stems are used to make flower pots and other plant supports for gardening (also popularly known as xaxims).
- Pteridophytes Review - Image Diversity: xaxim
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