Classification of Pteridophytes (6 ways) with Examples microbiologystudy

The classification of pteridophytes has undergone various changes over the years. The traditional system of classification of vascular plants was based on the presence or absence of seeds.

The vascular plants that possess seeds were included under the division Spermatophyta and those that do not produce seeds were placed under Pteridophyta.

According to the traditional system, Pteridophytes are divided into the following classes.

Class Psilophytineae

It includes two orders:

1. Order Psilotales– It includes species like Psilotum.
2. Order Psilophytales– It includes Rhynia.

Class Lycopodineae

It includes three orders-

1. Order Lycopodiales– It includes species like Lycopodium
2. Order Isoetales– It includes Isoetes.
3. Order Lepidodendrales– It includes Lepidodendron species.

Class Equisetineae

It includes two orders-

1. Order Equisetales– It includes species of Equisetum.
2. Order Sphenophyllales– It includes Sphenophyllum species.

Class Filicineae

It includes five orders-

1. Order Filicales– It includes species of Dryopteris, Marsilea.
2. Order Marattiales– It is represented by genus Marattia.
3. Order Ophioglossales– It includes Ophioglossum and Botrychium species.
4. Order Osmundales– It includes Osmunda species.
5. Fossil Orders 

Later some fern-like seed-bearing plants were discovered. This discovery eliminated the distinction between pteridophyta and spermatophyta. Based on origin and development, Sinnott introduced the term “Trachaeophyta” for all those plants having vascular arrangements including bryophyta and thallophyta.

The revised system of classification is as follows- 

Division: Trachaeophyta

It has four sub-divisions: 

Subdivision- Psilopsida

Class Psilophytineae– It includes two orders:

1. Order Psilotales
2. Order Psilophytales

Sub division- Lycoposida

Class Lycopodineae– It includes four orders:

1. Order Lepidodendrales
2. Order Lycopodiales
3. Order Pleuromeiales
4. Order Isoetales

Subdivision Sphenopsida

Class Equisetineae– It includes three orders:

1. Order Equisetales
2. Order Sphenophyllales
3. Fossil orders

Subdivision Pteropsida

The term here is used in a restrictive sense to cover the megaphyllous pteridophytes only.

Class Filicineae– It includes five orders

1. Order Ophioglossales
2. Order Filicales
3. Order Osmundales
4. Order Marattiales
5. Fossil orders.

Smith divides the vascular cryptogams into four divisions:

• Division Psilophyta
• Division Lepidophyta
• Division Calamophyta
• Division Pterophyta

One of the most widely accepted modern classifications is given below-

Division Psilophyta

It includes two classes-

• Class Psilophytopsida – It includes the order Psilophytales.
• Class Psilotopsida– It includes order Psilotales.

Division Lycophyta or Lepidophyta

It includes two classes-

• Class Eligulopsida – It includes homosporous forms with ligulate leaves.

 It includes Order Lycopodiales

• Class Ligulopsida– This class includes heterosporous forms with ligulate leaves. It includes four Orders: Selaginellales, Isoetales, Pleuromeiales, Lepidodendrales.

Division Arthrophyta or Calamophyta or Sphenophyta

It includes two classes- 

• Class Sphenophyllopsida- This class includes extinct genus- sphenophyllum which is placed in the following order- Sphenophyllales.
• Class Calamopsida– It includes both fossil and living forms. It has one order- Equisetales.

Division Filicophyta or Pterophyta

It includes four classes-

• Class Eusporangiopsida– It includes two orders- Ophioglossales and Marattiales
• Class Protoleptosporangiopsida– It includes order Osmundales.
• Class Leptosporangiopsida– It includes three orders- Filicales, Marsileales and Salviniales.
• Class Primopteropsida– It includes two orders- Cladoxyales and Coenopteridales.

Reimers (1954) classified Pteridophytes as follows:

Class A- Psilophytopsida

It includes the order Psilophylaes.

Class B- Psilotopsida

It includes the order Psilotales.

Class C- Lycopsida

It includes five orders: Protolepidodendrales, Lepidodendrales, Lycopodiales, Selaginellales, Isoetales

Class D- Sphenopsida

It includes four orders: Hyeniales, Sphenophyllales, Calamitales, Equisetales

Class E- Pteropsida

It includes four sub-classes-

• Subclass- Primofilices: It includes two orders: Cladoxytales and Coenopteridales.
• Subclass- Eusporangiate: It includes two orders: Marattiales and Ophioglossales.
• Subclass- Osmundidae: It includes the order Osmundales.
• Subclass- Leptosporangiatae: It includes three orders: Filicales, Marsileales, Salviniales

Out of all these orders, Protolepidodendrales, Lepidodendrales, Hyeniales, Sphenophyllales, Calamitales, Primofilices, Cladoxytales, and Coenopteridales are fossils.

Cronquist, Takhtajan, and Zimmerman classified Pteridophytes as follows:

Division Rhyniophyta

It includes Class Rhyniatae and Order Rhyniales

Division Psilotophyta

It includes Class Psilotatae and Order Psilotales

Division Lycopodiophyta

It includes two classes:

• Class Lycopodiatae– It has five orders- Asteroxylales, Drepanophycales, Protolepidodendrales, and Lycopodiales.
• Class Isoetatae– It includes four orders Lepidodendrales, Pleuromiales, Isoetales, and Selaginellales.

Division Equisetophyta

It includes two classes:

• Class Sphenophyllatae– It includes orders Sphenophyllales, Pseudoborniales.
• Class Equisetatae– It includes orders Calamitales and Equisetales.

Division- Polypodiophyta

It includes Class Polypodiatae which is again divided into five sub-classes:

• Sub-Class: Protopteridiidae
• Sub-Class: Archaepteridiidae
• Sub-Class: Ophioglossiidae
• Sub-Class: Noeggerothiidae
• Sub-Class: Marrattidae
• Sub-Class: Polypodiidae
• Sub-Class: Marsilleidae
• Sub-Class: Salviniidae

These sub-classes are further divided into orders.

The modern system of classification of pteridophytes includes seven divisions which are mentioned below:

1. Rhyniophyta

Rootless plant body which was differentiated into rhizome and an aerial leafless portion arising from underground rhizome. The aerial branches were dichotomously branched, some of which bear terminal sporangia. Sporangia are homosporous, thick walled and their development is eusporangiate. Spores were in tetrads. Stems cylindrical, vascular anatomy show lobed protosele and xylem was centrarch.

2. Trimerophytophyta

Plant body has monopodial branching in its main axis whereas lateral axis has dichotomous or trifurcate branching. Surface of both axis were smooth, punctuate or spiny. Branching differentiated into fertile and sterile axes. Fertile branches bear terminal sporangia which were aggregated at tips of dichotomous branches. Sporangia homosporous and development in eusporangiate. Stem solid, with protostele and centrarch xylem.

3. Zosterophyllophyta

Plant body rootless, leafless and branched dichotomously or pseudomonopodially. Stem protostelic with exarch xylem, xylem strands elliptic or terete with scalariform tracheids. Sporangia borne on the lateral stem tips, globose or reniform in shape; which were often aggregated into terminal clusters.

4. Psilophyta

Plant body is differentiated into an underground rhizome and aerial shoot. Underground rhizome is covered with rhizoids, true roots absent, aerial shoots bear minute scale-like lateral appendages. Two or three lobed synangia associated with fertile appendages are found on aerial shoots. Plant homosporous, multiciliate antherozoids present. Development of embryo is exoscopic and is without a suspensor.

5. Lycopodiophyta

Plant body well differentiated into root, stem, and leaves. Leaves are microphyllous with single vein. Vascular tissue system is devoid of leaf gaps. Sporangia borne on adaxial surface of fertile leaf known as sporophyll. Plants homosporous as well as heterosporous. Antherozoids bi-to multiciliate, development of embryo is endoscopic.

6. Sphenophyta

Plant body is differentiated into leaf, stem and root, whorls of simple leaves are found on notes of stems. Internodes of stem and branches longitudinally ridged. Leaf gaps absent in vascular arrangement of stems. Sporangia borne on sporangiophore. Number of sporangia on sporangiophore may vary from one to many, antherozoids are multiciliate. Embryo development is exoscopic and embryo lacks a suspension.

7. Pterophyta

Plant body is differentiated into leaf, stem and root, leaves are prominent and megaphyllous. Leaf gaps are found in protostelic stem. Sporangia usually borne on margin or abaxial surface of fertile leaves. Antherozoids multiciliate and embryogeny may be either exoscopic or endoscopic.

Characters of living pteridophytes viz. Psilophytes, horsetails, club-mosses and ferns are given below-

Psilophyta- 

• Sporophyte- Plant is rootless, dichotomously branched rhizomes with erect, aerial branches. Leaves spirally arranged scale-like. Sporangia thick-walled, spore homosporous.
• Gametophyte- Non-photosynthetic, cylindrical, covered with rhizoids and bearing both antheridia and archegonia. It is similar to the rhizomes of sporophytes.
• Ecology- Terrestrial or epiphytes.

Sphenophyta (Horsetails)-

• Sporophyte- Roots present, stem rhizomatous with erect, aerial branches. Leaves are whorled. Sporangia thick-walled, homosporous, aggregated in a terminal strobilus.
• Gametophyte- Either male or initially female, becoming hermaphrodic, Sex-ratio of germinating spores apparently controlled by light intensity and crowding.
• Ecology-Usually perennial, usually mesophytes or hygrophytes.

Lycopodiophyta(Clubmosses)-

• Sporophyte– Roots present, stem creeping or erect or pendulous. Leaves spirally arranged. Sporangia thick-walled homosporous or heterosporous, aggregated in a terminal strobilus.
• Gametophyte is free-living or endoscopic.
• Ecology– Usually terrestrial, some are epiphytic or aquatic.

Pterophyta (Ferns)-

• Sporophyte- Root present, stems creeping, rhizomatous or erect. Leaf spirally arranged, compound. Sporangia thick or thin walled, homosporous or heterosporous, terminal on axes or on lower surface of leaves.
• Gametophyte– Free living or endoscopic.
• Ecology- Widely distributed, epiphytic, terrestrial or aquatic.

References

1. Hait, G., Bhattacharya, K., & Ghosh, A. K. (2012). A textbook of Botany, Volume I.
2. Pteridophyta by B.R. Vashishta, A.K. Sinha, Adarsh Kumar (S.Chand & Company ltd)
3. Smith, R.W. (1900). Bot. Gaz., 29 : 228-58; 333-46
4. Rashid, A. (1999). An Introduction to Pteridophyta : Diversity Development. Differentiation. Vikas publishing House Pvt. Ltd. New Delhi.
5. Smith, G.M. (1955). Cryptogamic Botany, Vol. 2. New York and London.
6. Pteridophytes and their classification — lesson. Science State Board, Class 8. (n.d.). https://www.yaclass.in/p/science-state-board/class-8/plant-kingdom-14831/the-classification-of-plants-5639/re-b4933bf5-19fe-437e-8d5e-2e2bb304e74e
7. Classification of Pteridophyta. (2022, April 14). Unacademy. https://unacademy.com/content/neet-ug/study-material/biology/classification-of-pteridophyta/
8. GeeksforGeeks. (2023, September 20). Pteridophyta Definition, Characteristics, Classification, uses. GeeksforGeeks. https://www.geeksforgeeks.org/pteridophyta-definition-characteristics-classification-uses/
9. Kato, M. 1983. Classification of major groups of pteridophytes. J. Fac. Sci. Univ. Tokyo III, 13: 263–283.
10. Tryon, R. M. 1952. A sketch of the history of fern classification. Ann. Missouri Bot. Gard. 39: 255–262.